Hematology and Immunology Flashcards

Question

Antinuclear antibodies Serum ANAs are a hallmark of human, canine, and feline SLE. Indirect immunofluorescence or—less commonly—immunoperoxidase tests are used to detect ANAs, in which the antibodies bind to nuclei of a substrate tissue and are visualized with a fluoresceinated or enzyme-linked polyvalent secondary antibody. ANA testing is indicated when SLE is suspected on the basis of compatible clinicopathologic markers. Is a positive test result = SLE?

Answer 1

The results of the ANA test must be interpreted with caution: positive ANA results have been recorded in various canine diseases other than SLE, including rheumatoid arthritis, “idiopathic” immune-mediated polyarthritis, atopic dermatitis, symmetrical lupoid onychodystrophy, and black hair follicular dysplasia of Gordon Setters, animals with seroreactivity to Bartonella vinsonii subsp. berkhoffii, Ehrlichia canis and Leishmania infantum, hepatozoonosis,autoimmune thyroiditis, bacterial endocarditis, and neoplasia, pemphigus erythematosus, pemphigus vulgaris, and dirofilariasis. Similarly, up to 20% of normal dogs and 10% of normal cats may show low titers of ANAs, though high titers have occasionally been observed in healthy German Shepherd Dogs Positive results have also been documented in feline IMHA mm.... Occasional canine cases—typically less than 10%—fulfill many of the criteria for SLE and yet show negative ANA test results.

Answer 2

Animals showing clinicopathologic and radiographic evidence of erosive immune-mediated polyarthritis should be assessed for serum rheumatoid factor (RF), an autoantibody to the Fc region of an immunoglobulin G (IgG) molecule—usually of class IgM, but occasionally IgA or IgG—which may be found at low titer in 5% to 10% of healthy dogs and both dogs and cats with a range of infectious, inflammatory, and neoplastic diseases. Higher titers—usually greater than 1 : 40—are demonstrated in the majority of dogs and cats with RA, but may also be found in the serum of both canine and feline patients with nonerosive joint disease,* providing circumstantial evidence for the clinical overlap of such disorders. Cats with chronic progressive polyarthritis (periosteal proliferative polyarthritis)—an alternative differential diagnosis for erosive joint disease in this species—are usually seronegative for RF.

Answer 3

At least 95% of canine hypothyroidism is primary, associated with lymphocytic thyroiditis or idiopathic thyroid follicular atrophy. Some evidence suggests that follicular atrophy is a late consequence of thyroiditis, occurring at a time when inflammation has abated. Lymphocytic thyroiditis is thought to represent an autoimmune disease, characterized by focal and/or diffuse infiltration with lymphocytes, plasma cells, and macrophages. Antibodies against thyroid antigens are released into the circulation during the ensuing inflammation, including anti-T4, anti-T3, and antithyroglobulin (TG) autoantibodies (AAbs), all of which may have diagnostic utility.

Answer 4

TG-AAbs may be detected in ~35% to 60% hypothyroid dogs, consistent with a frequent diagnosis of autoimmune thyroid disease in this species. Furthermore, recent evidence suggests that approximately 20% of euthyroid dogs with TG-AAbs—but no other clinicopathologic signs of hypothyroidism—develop additional clinical or serologic abnormalities within a year of first recognition, suggesting that such cases should be monitored for eventual expression of hyothyroidism

Answer 5

(i) focal, in which the weakness localizes to the esophageal and pharyngeal musculature; (ii) generalized, in which the weakness shows a more global distribution; (iii) acute fulminating, in which the weakness shows a generalized distribution, but is acute in onset and severe in nature; (iv) paraneoplastic, in which neoplasia underlies the disease.

Answer 6

The molecular lesion underlying all of these forms of MG is an autoimmune response against acetylcholine receptors (AChRs) at the neuromuscular (NM) junction. Acquired MG may be associated with hypothyroidism, hypoadrenocorticism, other autoimmune disorders, thymoma, thymic cysts, cholangiocellular carcinoma, osteogenic sarcoma, anal sac adenocarcinoma, and dysautonomia. The onset or exacerbation of MG may be associated with bacterial or viral infection, and estrous cycles, gestation, or whelping may initiate or exacerbate MG in female dogs, prompting the recommendation to neuter these animals when they are clinically stable. The disease in cats is much less common than in dogs and is more often associated with a cranial mediastinal mass—19% of feline versus 3.4% of canine patients in comparative case series.

Answer 7

The gold standard for the diagnosis of acquired MG in both dogs and cats is the documentation of autoantibodies against muscle-type nicotinic AChRs by a species-specific immunoprecipitation radioimmunoassay, involving the precipitation of serum IgG and IgM antibodies binding to solubilized AChR complexed with a high-affinity peptide antagonist—labeled α-bungarotoxin. This test shows excellent sensitivity and specificity: while false positives are extremely rare AChR autoantibody titers should be measured every 6 to 8 weeks with treatment, since they may return to the normal range with clinical remission of the disease. Indeed, spontaneous remission of canine MG is also known to occur from a few weeks to 1 year following the initial diagnosis, though the mechanistic basis for this phenomenon remains unclear.

Answer 8

Masticatory muscle myositis is an idiopathic immune-mediated disease of the 2M myofibers of the muscles of mastication—the temporalis, masseter, rostral digastricus, and pteyroids—directed specifically at myosin. Clinical signs may include swelling and/or eventual atrophy of the muscles of mastication; jaw pain and trismus; and exophthalmos followed ultimately by enophthalmos, owing to swelling and then atrophy of the pterygoid muscles in the respective acute and chronic phases of the disease. Demonstration of autoantibodies against 2M myofibers of the temporalis muscle in an immunocytochemical assay—is diagnostic; showing high sensitivity (85% to 90%) and specificity (100%). More recently, an ELISA for 2M autoantibodies has largely replaced the immunohistochemical test, showing similarly impressive sensitivity and specificity

Answer 9

For example, prednisolone or prednisone is usually administered to patients with polysystemic immune-mediated disease, with the option of adding azathioprine or other cytotoxic agents as appropriate. The vinca alkaloids, notably vincristine, have been used for the treatment of ITP.

Answer 10

Discussion of the various classes of immunosuppressive drugs necessitates an understanding of the cell cycle, which is briefly reviewed here. The beginning of the cycle is marked by phase M, or mitosis, which is followed by a G1 phase (gap 1) characterized by RNA and protein synthesis of varying duration from tissue to tissue, sometimes extending up to days or weeks. From G1, cells may enter a resting, nonproliferating state (G0) in which they may remain for long periods of time—or from which they may return quickly to G1, to proceed with cell division. A period of DNA synthesis (S phase) follows G1 and generally lasts about 2 hours. This is succeeded by G2 (gap 2), another period of RNA and protein synthesis that generally lasts about 6 to 8 hours.

Answer 11

The immunosuppressive drugs described in the following paragraphs generally all inhibit proliferating immune cells, though their mechanisms of action and cell phase specificity vary widely. Owing to their potentially severe side effects and—in some cases—high cost, they are employed only when a definitive diagnosis has been reached.

Answer 12

• Gastrointestinal cytoprotection • Whole blood, or packed red cell, transfusions • Thromboprophylaxis • Danazol • Erythropoietin-α • Antihypertensive drugs • Diet • Topical skin products, avoidance of excessive sunlight • Splenectomy • Therapeutic plasmapheresis

Answer 13

Both aspirin and heparin have been used as thromboprophylactic agents in dogs. Aspirin irreversibly acetylates and thus inhibits platelet cyclooxygenase-1 (COX-1), preventing the synthesis of prostaglandin H2—the precursor of the platelet agonist thromboxane A2 (TXA2)—from arachidonic acid.

Answer 14

Vascular endothelial cells predominantly metabolize PGH2 to prostacyclin (PGI2), a molecule that inhibits platelet aggregation and induces vasodilation via the action of both COX-2 and COX-1.[526] Since aspirin inhibits COX-1 some 50 to 100 times more potently than COX-2 and platelets—in contrast to endothelial cells—cannot synthesize the inhibited enzyme de novo, aspirin can be dosed in such as way as to inhibit the prothrombotic effects of TXA2 without sacrificing the antithrombotic effects of PGI2. Thus, oral doses of aspirin as low as 0.5 mg/kg/day (“ultralow dose”) are thought to inhibit canine platelet function in vivo and have shown beneficial effects on survival of canine patients with IMHA without increasing the risk of gastrointestinal ulceration; ultralow dose aspirin is thus the author's first choice for thromboprophylactic therapy in canine IMHA.

Answer 15

Cats metabolize aspirin more slowly than dogs owing to reduced capacity of the glucuronidation pathway. Neither the conventional nor the lower dose of aspirin would be recommended alongside immunosuppressive doses of corticosteroids because of the risk of developing gastrointestinal ulcers. A recent review of PLN suggested that an ultralow dose of aspirin of 0.5 mg/kg PO every 48 hours could be given for thromboprophylaxis in cats with this disorder, though the evidence basis for this recommendation was unclear. Owing to the limited evidence for therapeutic benefit and the potential to do harm, the author does not administer aspirin to cats with IMHA. Nevertheless, with the advent of TEG in clinical practice and increasing recognition of the potential for TE in a variety of disorders, including PLN, there may be merit in considering low-dose aspirin therapy in those diseases associated with hypercoagulability when corticosteroids are not concurrently being administered.

Answer 16

Unfractionated heparin (UFH) comprises a mixture of variably sized glycosaminoglycan molecules with a mean molecular weight of 15 kDa; it is associated with unpredictable pharmacokinetic and pharmacodynamic (PK/PD) properties, the larger molecules tending to be eliminated more rapidly than the smaller. The administration of UFH by intravenous infusion—titrated against APTT according to a published nomogram—has been recommended as an initial therapy for PTE; however, the subcutaneous administration of UFH in the prophylactic setting is of questionable benefit, since close monitoring of effect by APTT or other coagulation tests would be impractical in outpatients.

Answer 17

Recent years have seen increasing interest in low–molecular weight heparins (LMWHs), comprising glycosaminoglycan molecules with a mean molecular weight of only 4 to 5 kDa. Like UFH, LMWHs bind to and amplify the activity of AT, though only 25% to 50% of the LMW molecules are large enough to inhibit factor IIa (thrombin), despite all being capable of inactivating factor Xa. The PK/PD profile of LMWHs is more predictable than that of UFH, though until more experience has been gained in the administration of these drugs to clinical patients initial therapy should still be guided by the recently validated anti–factor Xa assay or TEG, complementing careful clinical monitoring. Though these drugs have not yet been evaluated in the context of immune-mediated disease, they may have a place in this setting as an adjunct to ultralow-dose aspirin in canine patients with a particularly high risk of TE, or as a substitute for low-dose aspirin in feline patients receiving corticosteroids. dalteparin or enoxaparin, an alternative LMWH Therapy for DIC has traditionally centered on elimination or control of the inciting cause, if possible, alongside the transfusion of fresh frozen plasma and the administration of UFH. However, a recent experimental study has suggested that LMWH may also be efficacious in this setting and may in the future play a role in the therapy of DIC.

Answer 18

The thienopyridine drug clopidogrel, which irreversibly inhibits ADP receptors on the platelet membrane, has recently been evaluated as an antiplatelet agent in cats. A dose of 18.75 mg PO every 24 hours inhibited platelet aggregation in response to ADP and collagen—with an attendant increase in buccal mucosal bleeding times—in healthy domestic cats. To the author's knowledge it has not been administered at all to cats with immune-mediated disease to date, but as more is learned about this drug it may in the future offer a useful additional or alternative thromboprophylactic option in this species.

Answer 19

The genomic effects are mediated by binding to a cytoplasmic receptor, of which at least three isoforms are recognized in different tissues. 1. Following dissociation from plasma-binding proteins such as transcortin and albumin, corticosteroids either passively diffuse into the cell or engage with a plasma membrane receptor, which has been described in monocytes, B cells, and neutrophils; this membrane receptor is thought to mediate some of the nongenomic effects of these drugs. 2. A conformational change of the cytoplasmic receptor occurs following binding of the corticosteroid, which releases the heat shock and immunophilin proteins that associate with the receptor in the resting state. This activation event unmasks the DNA-binding domain of the receptor, which is then able to associate with specific DNA sequences called glucocorticoid responsive elements (GREs) following translocation to the nucleus. 3. The rate of transcription of nearby genes is either increased (positive GRE) or decreased (negative GRE), thereby inducing or inhibiting the translated proteins. (An example of a protein undergoing positive regulation is Iκβ, an inhibitory factor that associates with the transcription factor NFκβ, thereby preventing the up-regulation of several genes that do not themselves have GREs) 4. The receptor and corticosteroid are eventually metabolized by the liver and other target tissues, with renal excretion of inactive metabolites; the cellular half-life of the activated complex is approximately 10 hours.

Answer 20

Budesonide is a nonhalogenated glucocorticoid. Fluticasone propionate is an androstane glucocorticoid. Like budesonide, fluticasone undergoes extensive first-pass hepatic metabolism by the cytochrome P-450 system, yielding an inactive metabolite (17β-carboxylic acid) that undergoes biliary excretion. A recent study in healthy dogs revealed that fluticasone—like budesonide—suppresses the HPA axis, though less so than oral prednisone.

Answer 21

The purine analogs (azathioprine, 6-mercaptopurine), The antifolates (methotrexate) The pyrimidine analogs (5-fluorouracil, cytosine arabinoside), of which azathioprine is the drug most often used to treat immune-mediated disease.

Answer 22

The most commonly used of the thiopurines is azathioprine, which is converted to the active metabolite 6-mercaptopurine by the liver. Further hepatic metabolism to the active compounds 6-thioinosinic and 6-thioguanylic acids then occurs, followed by xanthine oxidase–catalyzed breakdown to thiouric acid, a metabolite that undergoes renal excretion.

Answer 23

Coadministration of the xanthine oxidase inhibitor allopurinol increases the intracellular concentrations of the active metabolites of azathioprine, prompting the recommendation in human medicine to administer azathioprine at one fourth to one third the usual dose if the patient is also receiving allopurin; similar hazards presumably also exist in veterinary patients.

Answer 24

The purine analogs compete with endogenous adenine and guanine, resulting in the formation of nonfunctional nucleic acid strands that prevent cellular proliferation; immunosuppression results from reduced DNA and RNA synthesis, with inhibition of coenzyme formation and mitosis. Both humoral and cell-mediated immunity are inhibited; the effects on T cells are profound and include the inhibition of inflammatory gene expression, induction of their apoptosis following activation, and suppression of their conjugate formation with antigen-presenting cells. Azathioprine may also reduce the elaboration of proinflammatory cytokines by monocytes and macrophages. While the immunosuppressive effect of azathioprine may theoretically take several weeks to become apparent, inhibition of lymphocyte blastogenesis in vitro was demonstrated in one study after only 1 week of therapy; though the in vitro system can never entirely recapitulate the behavior of the drug in vivo, these results accord with the author's impression that the clinical effect of azathioprine may be observed within the first 2 weeks of therapy when combined with corticosteroids.

Answer 25

Azathioprine has been used in the management of lymphocytic and granulocytic leukemias and various immune-mediated diseases, often being administered alongside a corticosteroid, thus capitalizing on its “steroid-sparing” effect. Several studies have suggested that azathioprine confers a beneficial impact on clinical signs and survival in canine IMHA: Provides a rationale for the coadministration of azathioprine with a corticosteroid in the management of canine IMHA, unless there is a specific contraindication against the use of this drug.

Answer 26

Azathioprine is generally well tolerated in the dog, but gives rise to profound and often irreversible myelosuppression if used above the safe dose of 0.3 mg/kg PO every 48 hours in the cat; since accurate dosing is difficult to achieve with 50-mg tablets and the therapeutic window of this drug is particularly narrow in cats, its use in this species is not recommended. Potential toxic manifestations of this drug in the dog include neutropenia, thrombocytopenia, anemia, acute pancreatitis, nonspecific gastrointestinal signs (vomiting and diarrhea), and hepatopathyeuromuscular blockade is a potential additional adverse effect in the cat.

Answer 27

Methotrexate acts as a reversible inhibitor of dihydrofolate reductase, an enzyme required for the conversion of folate to its active form, tetrahydrofolate, necessary for the synthesis of the purine nucleotides and thymidine; DNA synthesis is thereby inhibited, with suppression of both humoral and cell-mediated immune responses. Excretion of methotrexate and its metabolites occurs by both glomerular filtration and active transport across the renal tubules: delayed drug clearance—with the potential for toxicity—should be anticipated with renal disease, prompting the recommendation to avoid the drug, or to reduce its dose, in such patients.

Answer 28

Gastrointestinal, resulting in diarrhea, vomiting, and inappetence. (A number of other toxicities have either been documented in small animals or inferred from the human literature.Stomatitis, hemorrhagic enteritis, and intestinal perforation may occur in rare cases. Hepatotoxicity, renal tubular necrosis, alopecia, depigmentation, and interstitial pneumonitis with pulmonary fibrosis may also be observed. Bone marrow suppression, whose nadir occurs at 4 to 6 days, may result in mild anemia, neutropenia, and thrombocytopenia—side effects that may be exacerbated by the concurrent administration of a trimethoprim/sulfa antibiotic, which may lead to severe folate deficiency. Finally, encephalopathy may be observed with intrathecal administration and, rarely, anaphylaxis may be encountered) Leucovorin calcium, a derivative of tetrahydrofolic acid, antagonizes the effects of methotrexate and is a specific therapy for overdoses.

Answer 29

Cytosine arabinoside (cytarabine) is a synthetic nucleoside analog that is transported into the cell and is metabolized to the active form cytarabine 5′-triphosphate, which competitively inhibits DNA polymerase and thus DNA synthesis; the metabolite is ultimately incorporated into the DNA, thus inhibiting topoisomerase I and DNA repair. Cytarabine crosses the blood-brain barrier and has been traditionally administered to canine and feline patients as a component of combination protocols for the treatment of lymphoma and both lymphoid and nonlymphoid leukemias. Circulating cytarabine is rapidly metabolized by the enzyme cytidine deaminase present in the liver, kidneys, intestinal mucosa, and granulocytes, undergoing renal excretion.

Answer 30

Are dose-dependent and most commonly include myelosuppression and gastrointestinal upset.

Answer 31

Both drugs bind to tubulin, a dimeric protein resident in the soluble fraction of the cytoplasm, blocking its polymerization and leading to arrest of the cell cycle in metaphase. Vinca alkaloids also lead to the breakdown of preformed microtubules, which function in the maintenance of cellular structure and the provision of a conduit for secretions and the movement of neurotransmitters along axons. Interference with these functions may be responsible for both the increased release of platelets from megakaryocytes and the neurotoxic side effects of these drugs.

Answer 32

While vincristine is considered to be phase-specific, acting during mitosis, vinblastine also blocks the cellular use of glutamic acid, thereby inhibiting purine synthesis and the S phase of the cell cycle.

Answer 33

In the treatment of lymphoma and lymphoid leukemias, usually as a component of a combination protocol, but vincristine has also been administered to dogs with hemangiosarcomas, and vinblastine is used in the chemotherapy of mast cell tumors. Vincristine is also the drug of choice for the treatment of canine transmissible venereal tumor and vinblastine—less often associated with neurotoxicity—may be considered as an alternative to vincristine if a peripheral neuropathy has developed in the course of treatment. Vincristine has also been used in the therapy of ITP, either being administered intravenously as a bolus injection or used to load platelets prior to a transfusion of platelet-rich plasma (PRP). Loading the platelets with the vinca alkaloid in this manner targets toxic amounts of the drug to the reticuloendothelial system, thereby helping to eliminate the principal sink of platelets in ITP. Vincristine binds more avidly to platelets than vinblastine, so may be preferable for this mode of therapy.

Answer 34

Vincristine is generally not myelosuppressive in the dog, though it may occasionally induce significant neutropenia in the cat. Vinblastine has myelosuppressive activity in both species, the nadir for neutrophil counts usually occurring within 4 to 9 days of administration; recovery after withdrawal of the drug usually takes from 7 to 14 days. Both of the vinca alkaloids must be given intravenously, since they act as severe irritants in the extravascular tissues, leading to pain, necrosis, and even tissue sloughing. Inappetence, nausea, vomiting and constipation may be observed with both vincristine and vinblastine in the dog and cat. One of the more debilitating side effects of long-term treatment with vincristine and, rarely, vinblastine is the development of an iatrogenic sensory and motor neuropathy, seen most often in cats. Neuronal degeneration with axonal swelling may occur, with secondary demyelination of peripheral nerves; if therapy is not immediately stopped, severe, generalized motor weakness may develop. Signs of the neuropathy generally abate in the months following cessation of therapy, though some of the lesions may be irreversible. Pulmonary edema has also recently been documented in a cat with chronic lymphocytic leukemia given vincristine as part of a combination chemotherapy protocol.

Answer 35

The calcineurin inhibitors, ciclosporin and tacrolimus (formerly FK506), function by binding to specific intracellular receptors called immunophilins: ciclosporin binds to cyclophilin, while tacrolimus binds to the FK506-binding protein. The heterodimeric complex thus formed then associates with and inhibits the calcineurin-calmodulin complex, a calcium-dependent serine-threonine phosphatase that results in the dephosphorylation of regulatory proteins.

Answer 36

Following translocation to the nucleus, the dephosphorylated regulatory proteins act as subunits of transcription factors such as NF-AT (nuclear factor of activated T cells), which promotes transcription of the interleukin (IL)-2 gene. The calcineurin inhibitors thus suppress transcription of key cytokines involved in the innate and adaptive arms of the immune response, including IL-2, a T cell growth factor, and interferon-α, a monocyte and macrophage activation factor; blockade of the transition from cell phase G0 to G1 thus occurs. Ciclosporin also inhibits the proliferation of canine keratinocytes and their synthesis of prostaglandin E2 following exposure to lipopolysaccharide, mechanisms that may contribute to its antiinflammatory and immunosuppressive action in the treatment of canine allergic skin disease. In addition, both ciclosporin and tacrolimus stimulate the activation of latent transforming growth factor-β via the generation of reactive oxygen intermediates, contributing to the excessive deposition of extracellular matrix that underlies the nephrotoxicity of these agents in humans.

Answer 37

Tacrolimus is 10 to 100 times more potent than ciclosporin but has a low therapeutic index and is associated with severe side effects in dogs, including inappetence, vasculitis, hepatotoxicity, and intestinal intussusception. Therefore, its systemic use in small animals cannot currently be recommended. However, topical tacrolimus has found utility in the management of canine atopic dermatitis, perianal fistulae, DLE, pemphigus erythematosus, pemphigus foliaceus, alopecia areata, and vitiligo, but usually only as an adjunctive or secondary treatment; furthermore, ocular tacrolimus has shown promise in the management of canine keratoconjunctivitis sicca, but the skin product (Protopic; Astellas Pharma) should not be placed in the eye since it contains propylene carbonate, an ocular irritant. As a topical therapy, tacrolimus is associated with minimal toxicity, showing neither atrophogenic nor adverse systemic effects; however, care should be taken to prevent the patient from inadvertently ingesting the drug by licking the area to which it has been applied.

Answer 38

Cyclosporine A, now known simply as ciclosporin, is a cyclic polypeptide metabolite extracted from the fungus Tolypocladium inflatum Gams. The drug is lipophilic and hydrophobic, and must be solubilized before administration. The intravenous preparation (Sandimmune Injection; Novartis) is an ethanol-polyoxyethylated castor oil mixture (Cremophor EL) that must be diluted in 0.9% sodium chloride or 5% dextrose in water prior to administration,[759] while the oral preparation (Neoral) and the veterinary-licensed product Atopica; Novartis) is a micro emulsion formulation C

Answer 39

Ciclosporin tends not to be nephrotoxic or hepatotoxic in dogs and cats at the doses recommended in the veterinary literature—in contrast to the susceptibility of human patients to such toxicities—and is generally well tolerated in these species. Long-term ciclosporin therapy may also increase the probability of neoplasia—in particular lymphoma—especially with concurrent prednisone or prednisolone therapy. Other side effects noted in dogs have included vomiting, diarrhea, weight loss, gingival hyperplasia, papillomatosis, involuntary shaking, inhibition of insulin release, and peripheral insulin resistance—all signs that tend to abate with a reduction in dose. Finally, hirsutism may be observed in both dogs and cats

Answer 40

Alkylating Agents: These drugs possess alkyl radicals that react covalently with DNA, causing breaks in the molecule and cross-linking of the twin strands, actions that interfere with DNA replication and RNA transcription. These agents thereby inhibit protein synthesis in resting cells, prevent mitosis, and kill dividing cells. This group includes cyclophosphamide, ifosfamide, chlorambucil, melphalan, mechlorethamine, nitrosoureas (carmustine and lomustine), procarbazine, and dacarbazine, though only chlorambucil is in current use as an immunosuppressive drug in small animals.

Answer 41

Chlorambucil is the slowest acting and least toxic of all the alkylating agents commonly used in veterinary medicine; myelosuppression—which is dose-related—is generally not observed until the drug has been administered for at least a month, and is usually reversible within a 2-week period if noted sufficiently early. Additional side effects may include inappetence, vomiting and diarrhea, referable to gastrointestinal toxicity, generalized myoclonus, and grand mal seizures, which have been observed in cats receiving high-dose pulse therapy.

Answer 42

Chlorambucil is used in combination chemotherapy protocols for chronic lymphocytic leukemia, low-grade lymphoma, intermediate to high-grade lymphoma (maintenance protocols), mast cell tumors, multiple myeloma, and to replace cyclophosphamide in cases of sterile hemorrhagic cystitis. It has also found utility as an adjunctive immunosuppressive agent in the treatment of canine and feline pemphigus foliates, feline eosinophilic granuloma complex, and a variety of immune-mediated diseases in cats (e.g., IMHA, ITP, and IBD) when used in combination with corticosteroids. Corticosteroids and chlorambucil may also benefit patients with membranous GN, which results from the deposition of immune complexes—most often containing IgG—onto the subepithelial aspect of the glomerular basement membrane. In common with many of the alternative immunosuppressive drugs in the dog and cat, objective evidence for the efficacy of chlorambucil in this and other potential indications is currently lacking; further work is required in this area. Various studies have demonstrated the neutral or negative impact of cyclophosphamide on the outcome of IMHA,and the author does not therefore recommend the use of this drug for small animal immune-mediated disease.

Answer 43

Intravenous Immunoglobulin Human intravenous immunoglobulin (hIVIG) is a purified preparation of polyspecific IgG derived from the pooled plasma of healthy blood donors, used in human medicine to provide passive immunity in patients with primary or secondary immunodeficiency syndromes and in the treatment of a number of immune-mediated disorders, including chronic inflammatory demyelinating polyneuropathy and multifocal motor neuropathy; ITP, IMHA, autoimmune neutropenia and pure red cell aplasia; acute, decompensating MG etc. Each preparation contains antibodies from across the spectrum of the normal human IgG repertoire, including antibodies to external antigens—for example, from food, intestinal bacteria, pathogens—and autoreactive and antiidiotypic antibodies (an idiotype is an antigenic determinant of the variable region of an antibody: antiidiotypic antibodies are those with specificity for other antibodies); hIVIG also contains traces of IgA, IgM, Th2 cytokines and cytokine antagonists. While the mechanisms of action of hIVIG have not all been fully elucidated, they are thought to include:and both Abs and antagonists of Th1 cytokines within the IVIG product; (vii) inhibition of the differentiation and function of dendritic cells, in part by enhancing the production of IL-10; (viii) prevention of the generation of the membrane attack complex (C5b-9), by scavenging active complement components and diverting them away from cellular targets; and (ix) inhibition of leukocyte recruitment to inflamed tissues, by direct inhibition of selectin and integrin function. Most of these mechanisms remain unsubstantiated in small animals, but binding of hIVIG to canine lymphocytes and monocytes has been demonstrated, the latter Fc-mediated. Furthermore, the ability of hIVIG to inhibit phagocytosis of antibody-coated canine RBCs was confirmed using a mononuclear cell phagocytic assay. hIVIG has been employed alongside conventional immunosuppressive therapy in various immune-mediated diseases of dogs, including: (i) nonregenerative anemia, in which reticulocytosis was observed within 1 to 4 days of administration in five of five dogs; (ii) IMHA, in which hIVIG appeared to elicit an increase in PCV of at least 4% within 3 to 4 days in 10 of 13 dogs, an increase in hemoglobin concentration of at least 2 g/dL within 14 days in 8 to 10 dogs, and a potential beneficial effect in 9 dogs, which showed similar mortality to 13 patients not receiving hIVIG despite suffering from more severe disease; (iii) severe ITP, in which 4 of 5 dogs showed an apparent response to treatment, the mean platelet count increasing from 2500/µL to 50,600/µL 24 hours after infusion; (iv) concurrent IMHA and ITP (Evans' syndrome) in a diabetic Miniature Schnauzer immunosuppressed only with leflunomide and hIVIG, the platelet count increasing from 2000/µL to 116,000/µL within 24 hours of the infusion; and (v) various immune-mediated skin diseases Several authors have hypothesized that hIVIG may allow a temporary cessation of erythrolysis in IMHA, thus allowing additional time for other forms of treatment to become effective. Indeed, the short half-life of hIVIG in dogs (7 to 9 days, suggests that its benefits may be limited to the short term, supported by its apparent inability to improve long-term survival of canine patients with IMHA in one study.

Answer 44

Immune-Mediated and Infective Arthritis: Immune-mediated and infective arthritis form the two main categories of inflammatory arthropathy and are characterized by an elevated white cell count in the synovial fluid, mainly comprising neutrophils. Synovial fluid analysis is mandatory for diagnosis of these conditions, and it distinguishes them from the more common degenerative arthropathies. Infective arthritis is defined as an inflammatory arthropathy caused by an infective agent that can be cultured from the affected joint or joints; however, it is not always possible to culture the organism, and it is important to assume infection where only a single joint is affected with an inflammatory type of arthritis. Bacteria are the most common cause of infective arthritis

Answer 45

Immune-mediated arthritis is defined as an inflammatory disease where microbial organisms cannot be cultured from the joints and where the immune system plays an important role in its pathogenesis, in the form of immune complex formation, and autoimmunity. The failure to culture microorganisms does not rule out their involvement, but unlike the true infective arthropathies, there are no living organisms within the articular cavity. Unlike bacterial infective arthritis, they are generally polyarthropathies, although some of the more uncommon infections can involve multiple joints. Immune complex formation in response to microbial infection, either locally in the joint or systemically with subsequent deposition into the joint is a favored hypothesis. Transportation of microbial antigens to joints, with a subsequent immune response, is another possibility. Canine distemper viral antigens and antibodies have been identified in the immune complexes from the synovia of dogs with immune-mediated arthritis

Answer 46

1. BACTERIAL INFECTIVE ARTHRITIS (SEPTIC ARTHRITIS, SUPPURATIVE ARTHRITIS) 2. LYME ARTHRITIS 3. BACTERIAL L-FORMS AND ARTHRITIS 4. MYCOPLASMAL ARTHRITIS 5. FUNGAL ARTHRITIS 6. RICKETTSIAL ARTHRITIS 7. PROTOZOAL ARTHRITIS 8. VIRAL ARTHRITIS 9. IMMUNE-MEDIATED ARTHRITIDES 10. Erosive Immune-Based Arthritides: Rheumatoid Arthritis Periosteal Proliferative Polyarthritis 11. Nonerosive Immune-Based Arthritis Systemic Lupus Erythematosus Polyarthritis/Polymyositis Syndrome Polyarthritis/Meningitis Syndrome Sjögren's Syndrome Familial Shar-Pei Fever Polyarthritis of the Adolescent Akita Polyarteritis Nodosa Drug-Induced Arthritis Vaccination Reactions Idiopathic Polyarthritis

Answer 47

Autoimmune hemolytic anemia, Immune-mediated thrombocytopenia, Leukopenia, Glomerulonephritis, Dermatitis, Polymyositis, Pleuritis, Central nervous system (CNS) disease, and Symmetric polyarthritis SLE occurs in both dogs and cats, and because the clinical signs are so variable, diagnosis of the disease can be difficult.

Answer 48

The pathogenesis of SLE involves two main components, autoimmunity and immune complex hypersensitivity. Antibodies against red blood cells, platelets, and leukocytes are important in the development of hemolytic anemia, thrombocytopenia, and leukopenia; the deposition of immune complexes (possibly nuclear antigen and antinuclear antibody) in the kidneys (glomeruli), joints (synovial blood vessels), and skin (dermal/epidermal junction), and possibly in other organs, explains the inflammatory changes in these tissues. Joint radiographs may show no obvious abnormalities, although occasionally soft tissue swelling or synovial effusion is present.

Answer 49

SLE is characterized by the presence of circulating antinuclear antibody (ANA), a group of autoantibodies targeted against nuclear material.[37] Although ANA is found in various chronic disease states, a diagnosis of SLE according to some scientists cannot be justified unless the ANA test result is positive at a reasonably high titer. However, many veterinarians believe that the ANA test is completely nonspecific and, therefore, a test that should not be utilized in veterinary medicine, although tests that detect specific nuclear antigen antibodies might be more reliable.

Answer 50

Dogs with familial Shar-Pei fever present with episodes of fever (105° to 107° F) and with swelling of one or both hock joints and occasionally other joints. It is an autosomal recessive disease characterized by increased production of interleukin-6. In some cases the inflammation appears to be periarticular rather than within the joint itself and in these cases the synovial fluid cytology may be normal. Enthesiopathies are also seen and these animals appear to be susceptible to other problems such as immune-mediated renal disease and thromboembolism. The period between attacks is variable and an attack may be “triggered” by a stress situation that, if identified, might be avoidable, thus reducing the incidence of attacks. In some affected dogs, amyloid deposits occur in several organs, but renal amyloidosis and hepatic amyloidosis are the conditions most significant to the prognosis. Amyloidosis, when it occurs, will eventually result in renal or hepatic failure.

Answer 51

Drug-induced vasculitides are basically hypersensitivity reactions involving the deposition of drug antibody complexes around blood vessels in different areas of the body. The drug may act directly as an antigen or may combine with host proteins as haptens to form neoantigens. Polyarthritis is only one feature of these disease syndromes; fever, lymphadenopathy, and macular-papular or bullous-type hemorrhagic rashes are common. Thrombocytopenia, hemolytic anemia, polymyositis, retinitis, and glomerulonephritis are also reported. The most commonly incriminated drugs are antibiotics, particularly sulfa drugs, lincomycin, erythromycin, cephalosporins, and penicillins. The Doberman Pinscher appears particularly susceptible to sulphadiazine-trimethoprim.

Answer 52

• Type I: Uncomplicated idiopathic arthritis; this is the most common subgroup. • Type II: Idiopathic arthritis associated with infections remote from the joints (reactive arthritis). The infections commonly occur in the respiratory tract, tonsils, conjunctiva (e.g., Chlamydophila in the cat), urinary tract, uterine tract, skin (including anal furunculosis) and oral cavity. • Type III: Idiopathic arthritis associated with gastrointestinal disease (enteropathic arthritis). The gastroenteritis is usually characterized by vomiting and/or diarrhea. • Type IV: Idiopathic arthritis associated with neoplasia remote from the joints (arthritis of malignancy).

Answer 53

Osteoarthritis (OA) is a common and complex, progressive disease. In pathologic terms, OA has been defined as “an inherently noninflammatory disorder of movable (synovial) joints characterized by deterioration of articular cartilage and by the formation of new bone at the joint surfaces and margins.” From the etiopathogenesis perspective, it has been defined as “a complex of interactive degradative and repair processes in cartilage, bone and synovium, with secondary components of inflammation” and clinically, it may be defined as “a slowly evolving articular disease characterized by the gradual development of joint pain, stiffness, and limitation of motion.” OA is the most common arthropathy of dogs and cats. The inevitable progression of OA can largely be attributed to enzymatic degradation of the articular cartilage. The initiation of OA is not well understood, but several theories have been extended to explain how different stimuli may give rise to a progressive, degenerative disorder. The term primary osteoarthritis describes an important subset of OA in which there is believed to be a fundamental defect in the biomaterial properties of the articular cartilage. Normal loading then leads to progressive degradation of the cartilage matrix. Prevalence of primary OA increases with increasing age, but genetic factors may modify the age at onset and the progression of the disease.

Answer 54

Although OA is classed as a degenerative disorder, it has an important inflammatory component. A moderate to marked synovitis is seen in approximately 50% of surgical specimens from dogs with OA. The synovitis is characterized by hyperplasia and hypertrophy of synovial lining cells, villous proliferation, and a mild infiltration of lymphocytes, plasma cells, and mononuclear phagocytes.

Answer 55

NSAIDs act predominantly by blocking the inflammatory effects of prostaglandins through inhibition of the breakdown of arachidonic acid by cyclooxygenase (COX); some NSAIDs also inhibit lipoxygenase, thus inhibiting leukotriene production. Research has shown that there are two principal forms of COX, an endogenous form, COX-1, and an inducible form, COX-2. The endogenous form is responsible for the production of protective prostaglandins that help to maintain the integrity of the gastric mucosa and vascular endothelium and to protect renal blood flow in times of circulatory crisis. COX-2 is produced as part of the inflammatory response, responsible for producing inflammatory prostaglandins such as PGE2. It has thus been proposed that NSAIDs that preferentially or selectively inhibit COX-2 or are COX-1 sparing are preferable since they are associated with fewer side effects. However, COX-1 does play an important part in the inflammatory process and pain perception and COX-2 is important in resolving inflammation. Recently, splice variants of COX-1 have been identified including COX-3 and partial COX-1 proteins (PCOX-1a and COX-1b).

Answer 56

Carprofen appears to be only a weak inhibitor of COX and its exact mode of action is not certain. Meloxicam preferentially inhibits COX-2; it is easy to administer as a liquid, mixed with food. Tepoxalin (TN Zubrin), a pyrazole derivative, is a dual inhibitor of both COX and lipoxygenase. Although it is not a preferential inhibitor of COX-2, there is evidence that it is tissue selective in its inhibition of prostaglandin production. The elimination pathway for tepoxalin is almost exclusively via the feces; only about 1% is found in the urine. This may help explain why renal toxicity is rarely encountered; it is the only NSAID licensed for use in dogs with renal impairment. The coxibs are a relatively new subgroup of COX-1–sparing NSAIDs, and two are currently used in the dog—deracoxib and firocoxib. Both appear effective with a good safety margin. They are as effective as other NSAIDs but appear to have fewer gastrointestinal side effects. The coxibs should be considered for dogs susceptible to gastrointestinal upset. Alternatively, the use of NSAIDs together with gastric protectants (e.g., sucralfate), H2 antagonists (e.g., ramitidine, cimetidine), or proton pump inhibitors (e.g. omeprazole) can minimize the gastrointestinal signs in susceptible animals. PGE agonists such as Misoprostol (a PGE analogue) can be used in severe cases. Paracetamol (acetaminophen) (in combination with codeine in the United Kingdom) is still sometimes used to treat OA in dogs.

Answer 57

All NSAIDs carry some risk of systemic side effects, particularly through damage to the gastrointestinal tract. Some NSAIDs cause a reduction in the glomerular filtration rate, which may be clinically significant in dogs with compensated renal failure. Carprofen has also been associated with hepatic toxicity in susceptible dogs. Furthermore, excretion of NSAIDs may be reduced in dogs with clinical or subclinical renal, cardiac, or hepatic disease. Such animals require lower doses to achieve therapeutic serum drug concentrations without risk of toxicity. Hepatic and renal parameters should be checked in all dogs before prolonged administration of NSAID therapy. Care should be taken if the dog is receiving other drug therapies since there may be competition for plasma protein binding.

Answer 58

There is much discussion as to the effects of NSAIDs on articular cartilage. Some of the older NSAIDs have toxic effects on chondrocytes in culture. In contrast, carprofen has been shown to stimulate chondrocyte activity in culture and to slow the progression of early OA in the experimental canine cruciate ligament model. Meloxicam has also been shown to have stimulatory effects on proteoglycan production in cartilage. The effect of the coxibs on cartilage is influenced by whether healthy or diseased cartilage is studied, but positive effects can occur.

Answer 59

An experimental study in the dog using the cruciate sectioning model has shown beneficial effects of intraarticular corticosteroids, both methylprednisolone acetate and triamcinolone. Overall the injected joints showed less cartilage erosion, less osteophyte production, less stromelysin activity, and less chondrocyte proliferation.

Answer 60

Pentosan polysulphate (PPS) is a semisynthetic glycosaminoglycan prepared from beech wood shavings and is structurally similar to heparin. It has been available as the sodium salt for several years and is given as a course of four weekly subcutaneous injections. A calcium salt (Na) is also available that can be given orally. Many actions have been attributed to PPS. Being structurally similar to heparin, the drug exhibits anticoagulant and fibrinolytic properties. Polysulphated preparations (most of these are injectable) should perhaps not be used in combination with NSAIDs since the former have anticoagulant properties and would perpetuate any gastrointestinal bleeds initiated by the NSAID.

Answer 61

Oral glucosamine sulphate is 90% absorbed and diffuses into the articular tissues.[32] In addition to the sulphate form, glucosamine is also available as the hydrochloride and as N-acetylglucosamine; although many different claims are made, there appears to be little difference in the efficacy of the different forms. Evidence does, however, favor glucosamine sulphate as being more effective, with the suggestion that the sulphate molecule itself might be clinically important, a factor that might also be relevant to chondroitin. Most nutraceutical preparations have glucosamine and chondroitin in combination. The manner in which the nutraceuticals should be used is also a matter of debate. They may be used on their own in clinically affected cases or in combination with NSAIDs, which is how the author most often uses them.

Answer 62

The essential fatty acids (EFAs) are normal constituents of cell membranes and are involved in lipid transport. They are also precursors to the eicosanoid family of inflammatory mediators. There are two main types of fatty acid, the omega-3 and the omega-6, and both these compete for incorporation into phospholipids and as substrates for COX and lipoxygenase. A higher proportion of omega-6 fatty acids within cell membranes is believed to promote the production of the inflammatory prostaglandins, leukotrienes, and thromboxanes. Diets containing omega-3 fatty acids (e.g., fish oils) and certain of the omega-6 fatty acids may help to reduce the production of proinflammatory prostaglandins within arthritic joints. In vitro studies have shown that the addition of omega-3 EFAs can prevent inflammatory and matrix degradative processes initiated by chondrocytes, specifically down-regulating aggrecanase activity.

Answer 63

Unlike the dog, most cases of OA in the cat appear to be of a primary or idiopathic nature. Secondary OA in the cat can be associated with previous trauma, and hip dysplasia can result in secondary hip OA; this accounts only for approximately 20% of hip OA, the rest being primary. Acromegaly is another cause of secondary OA. Overall, 60% to 75% of cases of OA in the cat appear to be idiopathic.

Answer 64

Meloxicam is thought to be metabolized by oxidative pathways and thus the relative low capacity for hepatic glucuronidation of exogenously administered drugs seen in the cat is not a problem. A molecular genetic basis for the latter has been identified; domestic cats have fewer hepatic UDP-glucuronosyltransferase (UGT) isoforms and may have mutations of UGT or pseudogenes

Answer 65

Meloxicam is highly protein-bound in the blood and thus care is always needed when it is given to a cat receiving other drugs, such as ACE inhibitors and diuretics, where there might be competition for protein binding. These cats should be particularly carefully monitored for possible side effects.

Answer 66

Defined as a reduction in the number of circulating red blood cells (RBCs), hematocrit, and hemoglobin, resulting in decreased oxygen-carrying capacity.

Answer 67

A normal animal will regenerate the erythron by accelerating erythropoiesis via erythropoietin-mediated effects on erythroid progenitor cells. Under accelerated erythropoiesis, reticulocytes leave the marrow early, causing an increase in number of circulating reticulocytes. The most reliable indicator of regeneration is an increase in aggregate reticulocytes in peripheral blood. After erythropoietin stimulates the marrow, it usually takes 2 to 5 days before reticulocytes can be identified in circulation, with peak numbers occurring 4 to 7 days following stimulation. Following severe acute blood loss, healthy dogs can increase reticulocyte production sixfold to eightfold, and cats threefold to fivefold.

Answer 68

Reticulocytes can be identified by staining cytoplasmic RNA with new methylene blue or brilliant cresyl blue and enumerated by hand or automated cell counters. Dogs normally produce only aggregate reticulocytes. In cats, aggregate reticulocyte counts more accurately reflect the regenerative state than do punctate reticulocyte counts; clinical pathology laboratories usually report aggregate reticulocyte numbers.

Answer 69

Normal dogs usually have less than 1 reticulocyte/100 erythrocytes and normal cats less than 0.4 reticulocytes/100 erythrocytes; however, it is more useful to evaluate aggregate reticulocyte counts as absolute reticulocyte counts. Healthy dogs usually have less than 60,000 and cats less than 42,000 reticulocytes/µL; higher values are suggestive of accelerated erythropoiesis. Other findings consistent with a regenerative response include polychromatophilia, anisocytosis, macrocytic and/or hypochromic indices, Howell-Jolly bodies (nuclear remnants), increased red cell distribution width (RDW), and appropriate rubricytosis.[

Answer 70

Regenerative anemias can be classified as those associated with hemolysis or those associated with acute or chronic blood loss. Rarely, cats with erythroid neoplasia have responsive anemias. The examination of the blood film may yield important information regarding the cause of the anemia, including hemoplasma, Babesia or Cytauxzoon organisms, spherocytes suggestive of immune mediated injury to erythrocytes, evidence of oxidative injury (Heinz bodies, eccentrocytes), or other changes in erythrocyte morphology (acanthocytes, schizocytes, keratocytes) that can be evidence of vasculitis, hemangiosarcoma, or intravascular coagulation. Bone marrow examination is rarely indicated in patients with regenerative anemias. An approach to the patient with regenerative anemia is presented in Figure 188-1. One of the most common causes of regenerative anemia of dogs is immune-mediated hemolytic anemia (IMHA).

Answer 71

Antibody-mediated RBC destruction is the hallmark of IMHA. Canine IMHA occurs most frequently (60% to 75% of cases) as an idiopathic disorder characterized by immune system dysregulation, antibody production against unaltered RBCs, and the absence of identifiable underlying disease. Less frequently, infectious diseases, neoplasia, or drug administration alter RBC surface antigens such that autoreactive antibodies are produced and secondary IMHA occurs. A causal relationship between development of IMHA and a possible predisposing factor can be difficult to prove and may more accurately reflect a temporal or coincidental association (e.g., hypothyroidism, bladder calculi, chronic renal failure), parallel manifestations of the same disorder (e.g., multisystemic autoimmune disease) or a nonimmunologic mechanism of hemolysis (e.g., envenomation)

Answer 72

In the setting of primary IMHA, the exact mechanism(s) by which loss of immunologic tolerance toward unaltered erythrocyte self-antigen(s) occurs is unknown. Mechanisms implicated in the initiation of autoreactivity in human IMHA include regulatory T-lymphocyte dysfunction, defective development of peripheral or central tolerance, exposure of previously ignored or hidden self antigens and cross reactivity between self and foreign antigens. Autoreactive T lymphocytes have been isolated from the peripheral blood of dogs with IMHA, suggesting loss of immunologic self-tolerance. Autoreactivity to spectrin is expected in hemolytic disease as a consequence of exposure to hidden RBC antigens and may represent a mechanism for removal of senescent erythrocytes, having been identified in clinically normal dogs.

Answer 73

Phagocytosis of opsonized RBC occurs following binding of the fragment crystallizable or constant fragment (Fc) of the immunoglobulin molecule to Fc receptors on cells of the mononuclear-phagocytic system. Appropriate Fc receptors are expressed on blood monocytes and hepatic Kupffer cells; however, the primary site of extravascular erythrophagocytosis is the spleen.

Answer 74

The interaction of RBC-bound autoantibody with macrophages results in either complete phagocytosis or partial internalization of a portion of the RBC membrane, followed by resealing of the membrane and reentry of the remaining red cell into circulation as a spherocyte. In addition, antibody binding can initiate complement fixation and formation of a transmembrane pore (membrane attack complex) with resultant intravascular osmotic hemolysis

Answer 75

Antibodies of the IgG subclass, alone or in combination with IgM, are the most commonly identified erythrocyte-bound immunoprotein in canine IMHA. Antibodies to only IgM or complement protein C3b were infrequently implicated as the autoreactive immunoprotein in older reports, but have not been identified using newer flow cytometric techniques.

Answer 76

IgG antibodies are relatively poor activators of the classical complement pathway and IgG-sensitized RBCs are generally eliminated through extravascular hemolysis. IgM-sensitized RBCs are generally eliminated through a combination of intravascular hemolysis (due to IgM-mediated activation of the classical complement pathway) and extravascular phagocytosis

Answer 77

The most common complication and cause of death in canine IMHA is confirmed or suspected thromboembolic disease (TED), including pulmonary thromboembolism (PTE) and disseminated intravascular coagulation (DIC). In addition to PTE, necropsy evaluations of dogs with IMHA have revealed evidence of thromboembolism in the spleen, lungs, kidneys, liver, heart, pituitary gland, stomach, skin, and lymph nodes.

Answer 78

thrombocytopenia, prolonged prothrombin time, activated partial thromboplastin time, low antithrombin activity, low fibrinogen concentration, increased fibrinogen degradation product concentration, increased D-dimer concentration

Answer 79

severe thrombocytopenia, hypoalbuminemia, negative direct antiglobulin test (DAT), intravenous catheterization, increased serum alkaline phosphatase (ALP)activity.

Answer 80

vasculitis, antiphospholipid antibodies, liberation of RBC stroma, tissue factor production and release from leukocytes and indirect procoagulatory effects of free hemoglobin Many of the suspected clinical risk factors for development of TED are unavoidable in treatment of the disease, including intravenous catheterization, administration of exogenous glucocorticoids or cytotoxic agents, and blood transfusion.

Answer 81

Increasing evidence suggests that a systemic inflammatory response coincides with the period of acute hemolysis in canine IMHA. The occurrence of an acute inflammatory response is supported by the findings of moderate to marked leukocytosis as well as by changes in the serum concentration of several acute phase proteins, including C-reactive protein, α-1 acid glycoprotein, ceruloplasmin, fibrinogen, von Willebrand factor antigen, and albumin. Severe systemic inflammation promotes a hypercoagulable state by increasing tissue factor expression, increasing fibrinogen concentration, increasing platelet responsiveness and P-selectin expression, and by inhibiting the production or activity of anticoagulant molecules including antithrombin, thrombomodulin, protein C, and plasminogen activators. The net result is an increase in procoagulant activity, a decrease in anticoagulant activity, and decreased fibrinolysis. The significant morbidity and mortality associated with canine IMHA despite apparently successful immunosuppression and appropriate supportive care suggests that the pathophysiology of this disease cannot be explained by autoimmunity and anemia alone. Rather, inflammatory processes and associated abnormalities in hemostasis could play a major role in the progression of this disease.

Answer 82

The American Cocker Spaniel (ACS) represents 11% to 33% of affected dogs. ACS who do not express dog erythrocyte antigen (DEA) 7 have been reported to be at increased risk for development of IMHA compared to an all-breed control population. However, the proportion of DEA 7–positive dogs did not differ between ACS with or without IMHA, suggesting the absence of DEA 7 may be a common feature of the breed regardless of disease status. Although differential representation of dog leukocyte antigen (DLA) class II haplotypes have been identified in dogs with IMHA compared to an all-breed control group, strong breed-associated DLA heterogeneity precluded identification of breed-specific associations between DLA haplotype and development of IMHA.

Answer 83

Although IMHA can occur in dogs of any age, it is most commonly a condition of young adult to middle-age dogs, occurring less frequently in dogs under 2 years of age. Female dogs have been indentified to be at increased risk of IMHA. A temporal association between vaccination and development of IMHA has been suggested (There is no evidence that vaccination increases the incidence of IMHA within the general population of dogs.)

Answer 84

Epistaxis, petechial hemorrhage, melena, or other bleeding tendencies may be the presenting clinical complaint in dogs with concurrent thrombocytopenia. Dogs with intravascular hemolysis may present with hemoglobinuria, a shorter history of illness, and more severe clinical signs. More specific indicators of extravascular hemolysis such as icterus, splenomegaly, and hepatomegaly are observed at presentation in 25% to 50% of cases.

Answer 85

A moderate to marked regenerative anemia, spherocytosis, and autoagglutination are characteristic of IMHA. However, the absence of one or more of these findings on a complete blood count (CBC) does not exclude the diagnosis. Blood smear evaluation is essential for identification of spherocytosis and RBC parasites and helpful for estimation of the adequacy of the regenerative response, leukocyte and platelet numbers.

Answer 86

Dogs with anemia of acute onset may present before sufficient time has elapsed for development of a regenerative response, but should demonstrate adequate reticulocytosis within 3 to 5 days. Persistent ineffective erythroid regeneration is suggestive of immune-mediated destruction of erythroid precursors, anemia of inflammatory disease, paraneoplastic syndrome, lack of erythropoietin (e.g., chronic renal insufficiency), or bone marrow disorders including myelophthisis, myelofibrosis and myeloproliferative disorders. Persistent nonregenerative anemia or leukopenia are indications for bone marrow aspiration and biopsy.

Answer 87

Moderate to marked leukocytosis is a common hematologic abnormality in dogs with IMHA Tissue necrosis secondary to anemic hypoxia and thromboembolism is the suspected stimulus for the leukocytosis The typical absence of leukocytosis with other anemic disorders is evidence of a cytokine response to inflammation and necrosis which is unique to IMHA.

Answer 88

Concurrent thrombocytopenia is identified in 25% to 70% of dogs with IMHA at the time of diagnosis and is typically assumed to be due to concurrent immune-mediated platelet destruction (Evans’ syndrome). Dogs with IMHA and concurrent thrombocytopenia should not be assumed to have concurrent immune-mediated thrombocytopenia (ITP) until evaluation for DIC has occurred. Failure to recognize DIC may explain why some reports have identified an association between thrombocytopenia and increased mortality.

Answer 89

Hyperbilirubinemia Although it is assumed that much of the hyperbilirubinemia is of prehepatic (hemolytic) origin, increased serum ALP alanine aminotransferase, and aspartate aminotransferase activities suggest hypoxia or drug-induced hepatocellular damage could contribute. Artifactual hypophosphatemia due to interference from hyperbilirubinemia and possibly hemoglobinemia has been described.

Answer 90

Decreased packed cell volume (PCV) with normal serum total protein concentration (total solids) is consistent with hemolysis. Intravascular hemolysis is suggested by the presence of hemoglobinuria and/or hemoglobinemia.

Answer 91

All dogs with suspected IMHA should be evaluated for the presence of RBC autoagglutination by means of a saline agglutination test. Briefly, one drop of EDTA-anticoagulated blood is combined with equal parts saline on a microscope slide. Persistence of RBC agglutination after saline dilution is suggestive of antibody-mediated clumping of cells.[40] However, microscopic evaluation of the saline-diluted RBCs is necessary to differentiate autoagglutination from rouleaux formation. If microscopic distinction between autoagglutination and rouleaux formation is not immediately obvious, further dilution of the patient sample with saline (1 part blood to 2 to 3 parts saline) or comparison to a comparably diluted control blood sample can be performed.

Answer 92

The direct antiglobulin test (DAT), or Coombs’ test, detects erythrocyte-bound immunoglobulin or complement, the presence of which is strongly supportive of a diagnosis of immune-mediated hemolysis. A positive slide agglutination test confirms the presence of erythrocyte-bound immunoglobulin and precludes performance of the DAT.

Answer 93

The DAT is performed via addition of species-specific antiserum containing antibody to one or more of IgG, IgM, or complement protein C3 to a suspension of washed patient erythrocytes. Interaction between erythrocyte-bound immunoglobulin or complement and the antiserum results in grossly visible agglutination of erythrocytes. Results are reported as the highest dilution of antiserum at which autoagglutination is observed. Hemolytic conditions, other than IMHA, that have been associated with DAT-positive anemia include acute or delayed hemolytic transfusion reactions, infection with erythrocyte parasites, drug-induced hemolytic anemia, lymphoproliferative disorders, and neonatal isoerythrolysis. DAT-negative canine IMHA, characterized by clinical evidence of hemolysis, absence of identifiable underlying disease, and a negative DAT, is a common clinical occurrence, with a reported incidence of 23% to 63%.

Answer 94

Low level of membrane-bound immunoglobulin or complement, low binding affinity or high dissociation constant of membrane-bound antibody, previous corticosteroid therapy, and technical error (e.g., improper antisera to antibody ratio, improper washing or dilution of cell preparations) (The use of flow cytometry for detection of anti-RBC antibodies is more sensitive and specific than regenerative anemia with spherocytosis for diagnosis of canine IMHA and more sensitive than direct antiglobulin testing for detection of anti-RBC antibodies. By flow cytometry, anti-RBC antibodies are detected in 17.7% and 8.3% of anemic and nonanemic dogs, respectively.[20] Among anemic dogs, anti-RBC antibodies are detected in 77%, 36%, and 4% of dogs with IMHA, thrombocytopenia, and neoplasia, respectively).

Answer 95

Descriptions of abdominal ultrasound findings in dogs with IMHA are limited. Hepatomegaly, splenomegaly and anechoic peritoneal effusion were the most common ultrasound findings reported in a study. Pleural and peritoneal effusions may occur as a consequence of thromboembolism or vasculitis while hepatomegaly and splenomegaly are assumed secondary to extravascular phagocytosis.

Answer 96

In summary, diagnostic criteria for primary canine IMHA include anemia (characterized by spherocytosis, autoagglutination and/or presence of anti-RBC antibodies [DAT or flow cytometry]), absence of identifiable underlying disease or predisposing cause, and negative or stable infectious disease titers, as indicated by the geographic region or travel history. Concurrent nonhematologic disease of presumed autoimmune etiology or positive antinuclear antibody titer should prompt consideration of a multisystemic autoimmune condition such as systemic lupus erythematosus (SLE).

Answer 97

Appropriate intravenous fluid support should not be withheld from anemic patients over concerns of further decline in Hct as vascular volume is essential to effective tissue perfusion. If concerns over the degree of anemia and associate clinical signs exist, a transfusion of packed RBCs should be administered rather than restriction of fluid therapy. Most dogs with IMHA (44% to 90%) have anemia of sufficient severity to require a blood transfusion. Compared to dogs that were not transfused, transfusion of packed RBCs to dogs with IMHA has been reported to increase survival without appreciable hemolytic transfusion reactions Administration of glucocorticoids at immunosuppressive doses is the foundation of acute and chronic treatment of canine IMHA

Answer 98

Although widely discussed in the human medical literature, the clinical relevance of the time-dependent metabolic and biochemical changes that occur in stored blood (e.g., loss of 2,3-diphosphoglycerol [2,3-DPG]) has not been thoroughly evaluated in veterinary patients. Until it can be determined whether the age of the transfused RBCs affects morbidity and mortality in canine IMHA, it is suggested that younger blood products be administered when possible.

Answer 99

Ideally, all patients requiring a RBC transfusion would receive a type and cross-match compatible blood product. As subjective interpretation of agglutination is the end point of both tests, interpretation of blood typing and cross matching can be hampered by persistent (i.e., despite saline washing) RBC autoagglutination.

Answer 100

Dogs with no previous history of transfusion or dogs having received their first transfusion no more than 5 days prior can receive DEA 1.1-negative blood products, “universal donor” (DEA 1.1, 1.2, 3, 4, 5, and 7 negative) blood products, or commercial bovine hemoglobin solution. A cross match must be attempted for all dogs with a history of blood product transfusion, as the presence of preformed alloantibodies increases the risk of acute hemolytic transfusion reaction. If persistent autoagglutination precludes interpretation of cross-match results, transfusion with universal donor blood or bovine hemoglobin solution may be required.

Answer 101

1. Rapid impairment of macrophage-mediated erythrophagocytosis, 2. Delayed (within 14 days) decrease in immunoglobulin concentration, & 3. Altered T lymphocyte generation and function secondary to decreased interleukin (IL)-6 production. The often slow or poor clinical response of intravascular hemolysis to glucocorticoid therapy could potentially be explained by the lack of immediate glucocorticoid effects on immunoglobulin and complement concentrations.

Answer 102

Prednisone and dexamethasone are the most frequently recommended glucocorticoid agents for initial treatment of canine IMHA. There is no documented advantage to higher corticosteroid doses or of one glucocorticoid over another.

Answer 103

Polyuria, polydipsia, polyphagia, panting, steroid myopathy, gastric ulceration, vacuolar hepatopathy, iatrogenic hyperadrenocorticism, cutaneous atrophy, and alopecia. Exogenous corticosteroid excess is a suspected clinical risk factor associated with TED in dogs, a significant cause of morbidity and mortality in canine IMHA.

Answer 104

Despite recommendations to reserve adjunctive immunosuppressive agents for dogs with severe disease (persistent autoagglutination, intravascular hemolysis, nonregenerative anemia) and dogs that fail to respond to initial glucocorticoid therapy, the negative side effects of glucocorticoids and the poor prognosis associated with the acute hemolytic crisis have resulted in a trend towards combination immunosuppression in canine IMHA. Due to its association with increased survival time, azathioprine has become the primary adjunctive immunosuppressive agent for canine patients with IMHA.

Answer 105

Azathioprine is a purine analogue antimetabolite, metabolized in the liver to 6-mercaptopurine and further converted to active cytotoxic thioguanine nucleotides. The thioguanine nucleotides act as purine antagonists and induce immunosuppression by impairing RNA, DNA and protein synthesis, thereby inhibiting lymphocyte proliferation without affecting absolute lymphocyte numbers or serum immunoglobulin concentration. Canine lymphocyte blastogenic response is significantly inhibited following 7 days of azathioprine therapy at a dose of 2 mg/kg/day and returns to baseline within 1 week of treatment cessation.

Answer 106

Acute pancreatitis, bone marrow toxicosis, hepatotoxicosis, gastrointestinal illness.

Answer 107

Cyclosporine binding of the intracellular protein cyclophilin and the resulting inhibition of calcineurin, prevent nuclear translocation of a family of proteins (nuclear factor of activated T cells) essential for transcription of the IL-2 gene. The absence of IL-2 prevents further activation and proliferation of T lymphocytes and secondarily results in IL-4, interferon-γ, and granulocyte colony-stimulating factor suppression, but does not affect peripheral lymphocyte count or serum immunoglobulin concentrations.

Answer 108

Gastrointestinal illness (specifically vomiting), gingival hypertrophy, papilloma-like skin lesions, and hair loss. (Increased susceptibility to opportunistic infections and cancer are accepted complications of chronic immunosuppression in human solid organ transplant recipients. Presumed infectious pneumonia and bacterial hepatitis due to Clostridium piliforme have been reported as causes of death in dogs receiving immunosuppressive treatment for IMHA. The risk of immunosuppression-related infection and neoplasia in canine IMHA warrants consideration before long-term immunosuppression is recommended.)

Answer 109

Development of thromboembolism is an important complication of canine IMHA; however, an ideal prophylactic anticoagulant has yet to be identified. Treatment with unfractionated heparin was not associated with prolonged survival in a study. While the ability of low–molecular weight heparins to inhibit coagulation via neutralization of Factor Xa may prove efficacious in canine IMHA, variable pharmacokinetics in veterinary species and increased cost currently limit their use. The identification of hyperresponsive, activated platelets in dogs with IMHA and improved short- and long-term survival in dogs with IMHA treated with aspirin (0.5 mg/kg/day) provide pathophysiologic and circumstantial clinical justification for antiplatelet therapy in acute IMHA. Aspirin exerts its antiplatelet effects by inhibition of cyclooxygenase-mediated synthesis of thromboxane A2, a powerful stimulant of platelet aggregation. Whether aspirin therapy effectively inhibits platelet aggregation in dogs with IMHA and whether this translates into decreased incidence of TED and increased survival is currently unknown.

Answer 110

There are few evidence-based guidelines pertaining to chronic monitoring and management of canine IMHA. Serial CBC evaluations (specifically Hct, resolution of autoagglutination, and spherocytosis) are used as an indication of response to initial therapy, continued disease remission and as a guide for tapering immunosuppressive medications. The ability of flow cytometry to quantify the percentage of RBCs with surface-bound immunoglobulin may prove useful for monitoring the effectiveness of immunosuppressive therapy. Evaluation of the patient by means of a history, physical examination, and CBC should be performed once to twice weekly until resolution of anemia, then biweekly until tapering of immunosuppressive medications is initiated.

Answer 111

While tapering (rather than abruptly discontinuing subimmunosuppressive glucocorticoid dosing regimens) theoretically permits recovery of the hypothalamic-pituitary axis, there is little evidence to justify tapering subtherapeutic doses of immunosuppressive agents such as azathioprine and cyclosporine.

Answer 112

Compared to dogs, primary IMHA occurs infrequently in cats. Nonimmunologic (e.g., toxicosis-related oxidative damage, inherited erythrocyte defects, hypophosphatemia) and immune-mediated hemolysis secondary to infection (e.g., feline leukemia virus [FeLV], Mycoplasma hemofelis, Cytauxzoon felis), drug reaction (e.g., methimazole, propylthiouracil), neoplasia (e.g., lymphoma), or other disease process (e.g., cholangiohepatitis) occur more frequently than the idiopathic, autoimmune form of the disease. Primary IMHA is reported to occur predominantly in younger (≤ 6 years), male, domestic shorthair/mixed-breed cats. The most frequently reported clinical signs and physical exam findings are lethargy, anorexia, pica, mucous membrane pallor, systolic heart murmur, and occasionally icterus.

Answer 113

Severe anemia at initial presentation (mean Hct of ≤ 12%) is characteristic of feline primary IMHA. The small size and lack of central pallor of the normal feline erythrocyte generally precludes identification of spherocytes. Although the severity of the anemia along with the insidious and nonspecific nature of the clinical signs are suggestive of a chronic condition, the anemia is generally nonregenerative (≥58% of cats) at the time of initial evaluation and may suggest immune-mediated destruction of erythroid precursors or pure red cell aplasia. Unlike the canine form of the disease, neutrophilic leukocytosis is uncommon. They can also present with neutropenia. Lymphocytosis and thrombocytopenia have also been described. In a recent study of cats with primary IMHA, serum biochemical abnormalities were generally limited to mild hyperbilirubinemia , hyperglobulinemia, hypoalbuminemia, and mild to moderate increases in serum ALP, alanine transferase, and aspartate transferase activities.

Answer 114

Among 19 cats with primary IMHA, macroscopic slide agglutination of erythrocytes was identified in all cats. Macroscopic agglutination in cats must be interpreted with caution given the propensity of feline erythrocytes for rouleaux formation. Autoagglutination should be confirmed by means of a saline agglutination test as described for dogs. Autoagglutination that persists despite saline washing and precludes performance of the DAT is described in 17% to 40% of feline patients. In the absence of identifiable underlying disease and persistent autoagglutination, the DAT is useful in identifying primary feline IMHA. Clinical evidence of intravascular hemolysis (i.e., hemoglobinemia, hemoglobinuria) has not been identified in feline primary IMHA despite IgM and C3b positive DAT results. Bone marrow aspiration and biopsy are indicated if persistent ineffective erythroid regeneration or multiple cytopenias are identified.

Answer 115

The tendency for hemolytic anemia in cats to be of secondary immune-mediated origin necessitates exclusion of underlying disease by means of serologic testing for retroviruses (FeLV and feline immunodeficiency virus [FIV]), negative blood film examination and/or polymerase chain reaction (PCR) for hemotropic Mycoplasma, normal diagnostic imaging or cytologic/histologic exclusion of neoplasia. While radiographic or ultrasonographic evidence of splenomegaly and/or hepatomegaly may reflect extramedullary hematopoiesis or extravascular hemolysis, enlargement of either organ should prompt cytologic evaluation for neoplasia, namely lymphoma or mast cell disease.

Answer 116

Supportive care of the feline IMHA patient is generally as discussed for the canine patient, including the likely necessity for RBC product transfusion. Assuming accurate pre transfusion blood typing or cross matching, blood product transfusion is safe in cats with hemolytic anemia and does not carry an increased risk of transfusion reaction or acute mortality compared to other anemic conditions. Multiple transfusions can be safely administered to cats with severe anemia.

Answer 117

Glucocorticoids (dexamethasone, prednisone, or prednisolone) are the initial recommended immunosuppressive agents. An empirical course of doxycycline in case of hemotropic Mycoplasma infection can be considered in the absence of PCR testing. Although based on very limited descriptions, cyclosporine and/or cyclophosphamide/chlorambucil have been administered in addition to glucocorticoids in nonresponsive or poorly responsive cases. Primary feline IMHA is associated with a lower overall mortality rate (24% to 32%) than the canine form of the disease possibly due to a lower incidence of thromboembolic complications. Recent retrospective reports suggest persistent or relapsed anemia necessitates protracted (possibly life-long) glucocorticoid therapy and/or alternate immunosuppressive regimens in up to 50% of cases.

Answer 118

OTHER HEMOLYTIC ANEMIAS Alloimmune Hemolysis: Transfusion Reactions Acute hemolytic transfusion reactions can develop when a dog or cat having preexisting antibodies to erythrocyte antigens undergoes transfusion with erythrocytes displaying those antigens. Binding of alloantigens (antigens occurring in a genetically different individual of the same species) by preformed alloantibodies leads to complement activation and intravascular hemolysis of the transfused erythrocytes.

Answer 119

In dogs, alloantibodies are produced during pregnancy, parturition, or after blood transfusion. Blood typing helps to identify potentially antigenic glycoproteins or glycolipids that are components of the erythrocyte membrane.

Answer 120

Although 12 or more DEAs have been identified, DEA 1.1, 1.2, and 7 are the most likely to induce alloantibody formation. However, transfusion reactions due to DEA 4 and the Dal blood types have been reported. Dogs do not have naturally occurring alloantibodies; thus initial exposure will not likely cause an acute transfusion reaction. However, once alloantibodies have been formed subsequent to exposure to alloantigens, only a small quantity of alloantigen is required to cause a transfusion reaction; there are enough erythrocytes and erythrocyte membrane fragments in fresh-frozen plasma to cause clinically significant acute reactions.

Answer 121

Feline erythrocyte antigens are termed type-A, type-B, or type-AB. The erythrocyte antigen Mik has also been recently described in domestic shorthair cats. The incidence of these blood types varies among cat breeds and geographic locations, with type A consistently being the most prevalent blood type.

Answer 122

Type-B cats have been most commonly identified in Australia, Turkey, Japan, and Europe. Breeds with increased prevalence of type-B blood include Abyssinian, Birman, Japanese Bobtail, Persian, Himalayan, Somali, Sphinx, Cornish Rex, British Shorthair, and Devon Rex; prevalence of blood types within breeds is influenced by geographic location. Type-AB cats are rare, and they do not produce alloantibodies.

Answer 123

In cats, alloantibodies occur naturally; however, the epitopes that induce these antibodies have not been identified. A severe reaction may occur on the initial exposure to blood, without prior sensitization by previous transfusion or pregnancy. The naturally occurring anti-B antibodies of type-A cats are weak agglutinins and hemolysins; if type-B blood is transfused into a type-A cat, the erythrocyte half-life falls to 2.1 days. Clinical signs associated with this mismatch are usually mild, and may include listlessness, tachycardia, tachypnea, hemoglobinemia, and hemoglobinuria.

Answer 124

Anti-A alloantibodies present in type-B cats appear to be strong hemolysins and agglutinins and can induce severe acute hemolytic transfusion reactions. If type-A blood is transfused into a type-B cat, the erythrocyte half-life falls to minutes to hours, and potentially fatal systemic anaphylaxis and hemolysis can follow. Clinical signs may include hypoventilation, apnea, vomiting, diarrhea, vocalization, arrhythmias, hemoglobinemia, and hemoglobinuria. Shock, systemic inflammatory response syndrome, multiorgan dysfunction syndrome, and DIC may ensue.

Answer 125

Blood typing and major cross matching reduce the possibility of a hemolytic transfusion reaction. It is not necessary to blood type or cross match a dog before the first transfusion. Sensitization occurs within 3 to 5 days of initial transfusion, and subsequent transfusion should be preceded by typing and major cross match. For cats, blood typing and major cross match should precede all transfusions.

Answer 126

Alloimmune Hemolysis: Neonatal Isoerythrolysis Neonatal isoerythrolysis is most commonly recognized in kittens, and occurs when type-A or type-AB kittens ingest colostrum containing anti-A alloantibodies from a type-B queen. Ingested alloantibodies are absorbed across the intestine, enter the blood, and attach to the neonate's paternally derived erythrocyte surface antigens. The opsonized erythrocytes are then lysed by macrophages or complement.

Answer 127

Kittens at risk are healthy at birth and nurse normally. Clinical signs develop hours to days following ingestion of colostrum, and variably include sudden death, weakness, failure to thrive, reluctance to nurse, dyspnea, hemoglobinuria, jaundice, and necrosis of the tail tip secondary to thromboembolism. A moderately regenerative anemia may be present, a Coombs’ test on the neonate will be positive and a cross match between the queen's serum and neonate's erythrocytes will be positive.

Answer 128

Anti-B alloantibodies of type-A queens have weak activity and are not usually associated with clinical signs. Type-AB cats do not produce alloantibodies. Neonatal isoerythrolysis is preventable if queens and toms of breeds with a high prevalence of type-B blood are blood typed prior to breeding.

Answer 129

In dogs, neonatal isoerythrolysis is rare, occurring when a DEA 1.1–negative bitch develops anti-DEA 1.1 antibodies after being transfused with DEA 1.1–positive blood, and then passes those antibodies to DEA 1.1–positive puppies. Affected puppies become pale within 1 to 2 days after birth; deaths may occur within the first 72 hours.

Answer 130

When oxidative injury exceeds the reductive capacity of the erythrocyte, hemoglobin is converted to HgbFe3+, which precipitates and aggregates as Heinz bodies on the inner surface of erythrocyte membranes. Erythrocytes with Heinz bodies are less deformable and more fragile than normal erythrocytes and are lysed in spleen. Additionally, there may be redistribution of band-3 proteins and formation of an antigen that is recognized by autologous antibodies, leading to secondary immune-mediated hemolysis.

Answer 131

In cats, Heinz bodies may be a normal finding due to inefficient splenic pitting of abnormal erythrocytes, and because feline hemoglobin has more sulfhydryl groups and is more prone to form more disulfide bridges than dogs. In addition, feline erythrocytes may have less reductive capacity than erythrocytes of other species.

Answer 132

While Heinz bodies do occur in dogs, oxidative injury of canine erythrocytes can be more localized to the erythrocyte membrane and cytoskeleton, leading to the formation of “eccentrocytes” (erythrocytes that have their hemoglobin shifted to one side of the cell).

Answer 133

Acetaminophen, benzocaine, n-propyl disulfide (onions, chives, garlic, leek, shallot, and related plants of the genus Allium), vitamins K1 and K3 (or possibly vitamin K antagonists rather than vitamin K), thiols in skunk musk, zinc (ingestion of zinc toys, pennies, pet carrier fasteners, zippers, zinc oxide).

Answer 134

acetaminophen, benzocaine, n-propyl disulfide.

Answer 135

The findings of regenerative anemia, evidence of hemolysis, demonstration of Heinz bodies on erythrocytes, history of exposure to an oxidant. It should be noted that zinc toxicity is usually associated with hemolytic anemia; however, Heinz bodies are present in only one third of affected dogs, that eccentrocytosis and mild spherocytosis can be present, and that a DAT can be positive.

Answer 136

Supportive care (including transfusion therapy if required), Semoval of zinc objects Possibly s-adenosyl-l-methionine (SAMe).

Answer 137

In humans, hereditary erythrocyte disorders are classified into those affecting heme/hemoglobin, erythrocyte membranes, or erythrocyte enzymes. Membrane disorders and erthroenzymopathies have been documented in dogs and cats; however, hemoglobinopathies have not been recognized in dogs/cats. These disorders are rare, and all have autosomal recessive inheritance, except for one form of feline porphyria, which appears to have autosomal dominant inheritance. The relatively more common hereditary erythrocyte abnormalities that cause anemia are described here.

Answer 138

Hereditary Hemolytic Anemias: Membrane Defects Stomatocytosis Stomatocytes are bowl-shaped macrocytes that have well demarcated slitlike pallor and increased fragility that is caused by the lack of a cytoskeletal protein. Affected individuals can have mild regenerative anemia. Hereditary stomatocytosis is reported in Alaskan Malamutes, Drentse Patrijshonds, and Miniature Schnauzers. The phenotype of affected Alaskan Malamutes includes chrondysplastic dwarfism; Drentse Patrijshonds have hypertrophic gastritis, hepatic bile duct proliferation, and abnormalities of the central nervous system. Affected Schnauzers have an otherwise normal phenotype.

Answer 139

Increased osmotic fragility Anemia caused by markedly increased osmotic fragility of erythrocytes, possibly caused by an inherited membrane defect, has been described in Somali, Abyssinian, Siamese, and Domestic Shorthair cats. Affected cats have recurrent anemia, splenomegaly, weight loss, lymphocytosis, and hyperglobulinemia. Some of these cats may respond to prednisolone therapy.

Answer 140

Hereditary Hemolytic Anemias: Erythroenzymopathies PFK is a rate-controlling enzyme of glycolysis. This disorder is caused by a mis-sense mutation of the muscle-type PFK gene, resulting in truncation and rapid degradation of the unstable protein. Homozygous affected dogs have persistent compensated hemolytic anemia.

Answer 141

Signs during crisis include? lethargy, anorexia, fever, icterus, hemolytic anemia, hemoglobinemia, and hemoglobinuria/hyperbilirubinuria. Signs of an exertional myopathy also occur, including exercise intolerance, muscle cramps, and mildly increased CK activity. Between crises, there may be persistent hyperbilrubinemia and reticulocytosis despite a normal Hct. Exercise, hyperventilation, excessive barking, or high ambient temperature can cause mild respiratory alkalemia.

Answer 142

Affected erythrocytes are extremely “alkaline fragile” due to reduced adenosine triphosphate (ATP) production and decreased 2,3-DPG concentrations, which leads to unstable erythrocyte membranes and hemolysis. PCR testing accurately discriminates between normal, carrier, and affected dogs. Affected dogs should not be encouraged to exercise, and carriers and affected dogs should not be bred.

Answer 143

Homozygous affected dogs usually show signs in first few weeks of life, which include decreased exercise tolerance, tachycardia, heart murmurs, pale mucous membranes, and splenomegaly. Erythrocyte R-type PK catalyzes the last ATP generation step of glycolysis; erythrocytes in homozygous affected dogs completely lack R-PK activity and express a fetal or leukocyte M2-PK that is not functional in erythrocytes.

Answer 144

Without PK activity, erythrocytes become ATP-deficient, membranes become defective, and hemolysis occurs. Prolonged hemolytic anemia in dogs results in excessive absorption of iron from the intestine, leading to iron overload. Iron overload causes progressive marrow (myelofibrosis, osteosclerosis) and hepatic injury (hemosiderosis, hemochromatosis, fibrosis, failure). Affected dogs usually die between 1 and 5 years of age.

Answer 145

These animals have moderate anemia, moderate to extreme reticulocytosis, mild to moderate icterus, and decreased erythrocyte PK (R-type) activity. PCR testing is available for Basenji, Beagle, Dachshund, Toy Eskimo, West Highland White Terrier, and Cairn breeds. PK enzyme testing with isozyme characterization is required to diagnose PK deficiency in other breeds. Total erythrocyte PK activity is reduced in cats with PK deficiency, with no M2 activity as in dogs.

Answer 146

The feline disorder may be asymptomatic, or cause chronic anemia or intermittent macrocytic hemolytic anemia and mild splenomegaly, but no osteosclerosis. Clinical signs are generally observed before 3 years of age.

Answer 147

The genetic defect is a splicing defect in the R-PK gene, causing a 13-base pair deletion. A molecular screening test is available. Because PK deficiency can be asymptomatic in cats, testing of Abyssinian and Somali cats used for breeding is recommended. Mean osmotic fragility of erythrocytes from cats with PK deficiency is usually within the reference range, differentiating this disorder from the osmotic fragility syndrome described in Abyssinian and Somali cats. Prednisone and splenectomy appear to ameliorate the clinical signs of intermittent anemia in cats with PK deficiency

Answer 148

Porphyrias are a group of hereditary disorders in which heme precursors accumulate in cells and body fluids because of deficient enzyme activity in the heme synthetic pathway. Cats with erythropoietic porphyria have hemolytic anemia and discolored (red, orange, or brown) teeth that fluoresce when irradiated with near-ultraviolet light. Porphyria in domestic shorthair cats is characterized by only a mild anemia, while porphyria in Siamese cats is can be associated with severe macrocytic, hypochromic anemia with poikilocytosis, Howell-Jolly bodies, and nucleated RBCs. Photosensitization, which has been described for other species, has not been seen in cats

Answer 149

Severe hypophosphatemia has been reported to cause extravascular hemolysis and Heinz body formation in dog and cats receiving insulin, hepatic lipidosis, enteral and parenteral hyperalimentation, and oral administration of phosphate binders.

Answer 150

Decreased ATP production, depletion of DPG, reduced glutathione; ......lead to increased erythrocyte fragility and susceptibility to oxidative injury and hemolysis. Management includes aggressive oral and parenteral phosphate supplementation.

Answer 151

Fragmentation of normal red cells can occur from mechanical trauma as they circulate though vasculature containing fibrin strands or abnormal rheologic forces. These microangiopathic hemolytic anemias are characterized by reticulocytosis and changes in erythrocyte morphology. Fragmented erythrocytes can appear as schistocytes (often triangular) or keratocytes (helmet-shaped).

Answer 152

DIC, vasculitis, hemangiosarcoma and other splenic disorders, hemolytic uremia syndrome, valvular heart disease, hepatic disease, glomerulonephritis, myelofibrosis, chronic doxorubicin toxicosis, heartworm caval syndrome, increased red cell fragility associated with severe iron deficiency, and potentially intravenous catheters.

Answer 153

The diagnosis of microangiopathic anemia is based upon finding mild to moderate anemia, no to moderate reticulocytosis, schistocytosis, and often thrombocytopenia and other evidence of a consumptive coagulopathy. Regardless of the degree of anemia, the finding of schistocytosis should prompt the clinician to search for disorders associated with abnormal microvasculature.

Answer 154

Hemolytic anemia has been reported to occur in dogs following envenomation by various snakes or the brown recluse spider. Phospholipase A and sphingomyelinase D are the components of venom suspected to have direct hemolytic effects. Spherocytic hemolytic anemia and neurologic dysfunction have been infrequently reported to occur in dogs following bee sting envenomation.

Answer 155

Components of bee venom suspected to have direct hemolytic properties include hyaluronidase, melitin, and phospholipase A. Prolonged hemolysis and successful treatment with glucocorticoid immunosuppression suggest development of an immunologic response against previously hidden erythrocyte antigens or altered erythrocyte membranes.

Answer 156

Histiocytic Disorders The hemophagocytic form of malignant histiocytosis/disseminated histiocytic sarcoma is characterized by invasion of phagocytic, neoplastic histiocytes arising from spleen and bone marrow macrophages with subsequent intravascular invasion and spread to the liver and lungs. Bernese Mountain Dogs, Rottweilers, and Golden, Labrador, and Flat-Coated Retrievers are most commonly affected.

Answer 157

The common features of regenerative anemia, thrombocytopenia, and splenomegaly can result in an initial misdiagnosis of IMHA/ITP. Normal or slightly increased serum bilirubin concentration, hypoalbuminemia, hypocholesterolemia, and DAT-negative anemia are features of hemophagocytic histiocytic sarcoma that may help differentiate hemophagocytic histiocytic sarcoma from IMHA.

Answer 158

Cytologic or histologic demonstration of erythrophagocytosis by neoplastic macrophages in spleen, bone marrow, liver, or lung. The disease is rapidly progressive and carries a grave prognosis for recovery.

Answer 159

Hemophagocytic histiocytic sarcoma should not be confused with hemophagocytic syndrome, a nonneoplastic proliferative disorder of macrophages characterized by peripheral bicytopenia or pancytopenia and more than 2% hemophagocytic macrophages in bone marrow aspirates. Hemophagocytic syndrome is differentiated from malignant histiocytic conditions by the lower percentage of histiocytic cells in bone marrow specimens, absence of cytomorphologic features of malignancy, and smaller macrophage size as determined by flow cytometric scatter plots. Hemophagocytic syndrome occurs as an idiopathic condition or in association with immune-mediated, infectious, neoplastic, and myelodysplastic disorders. Tibetan Terriers may be overrepresented. Although based on a limited number of cases, canine hemophagocytic syndrome generally carries a grave prognosis for recovery, with the possible exception of disease associated with a treatable infectious condition.

Answer 160

Blood Loss Anemia Bleeding from wounds—into the gastrointestinal or urinary tracts, or into the pleural, pericardial, or peritoneal cavities or subcutaneous tissues—may lead to acute or chronic anemia. Hemorrhage may be induced by trauma, ulceration, neoplasia, acquired or congenital factor deficiencies, von Willebrand disease, or thrombocytopenia/thrombocytopathia. Chronic iron-deficiency anemia has been associated with inflammatory bowel disease. Heavy hookworm, tick, or flea burdens may cause anemia, as can bleeding blood donors or frequent phlebotomy for diagnostic purposes.

Answer 161

During the first few hours following blood loss, fluid shifts from the extravascular space, causing anemia and hypoproteinemia, with proportionate decreases in albumin and globulin concentrations. Otherwise normal animals should respond with evidence of accelerated erythropoiesis in 3 to 4 days. If hemoperitoneum or hemothorax are present, the animal may autotransfuse, with resorption of approximately 80% of erythrocytes within 1 to 2 weeks.

Answer 162

History (including administration of nonsteroidal antiinflammatory drugs; pica is suggestive of iron deficiency), physical examination (including rectal examination for melena), and the findings of anemia, hypoproteinemia (if losses are external), and reticulocytosis (if there has been sufficient time for the marrow to accelerate erythropoiesis and the animal has not developed severe iron deficiency anemia). Urinalysis, testing for fecal occult blood, fecal examination for hookworms, and ultrasonographic examination of the abdomen, pleural, and pericardial spaces may be indicated. Management of acute blood loss anemia includes volume resuscitation, prevention of further hemorrhage, transfusion with appropriate blood products, and management of the underlying cause. When hemorrhage has been controlled, resolution of the anemia should occur within 1 to 2 weeks.

Answer 163

Hct and plasma protein concentrations may not change until fluid shifts occur (hours to days); thus the Hct may significantly underestimate the magnitude of acute blood loss.

Answer 164

Chronic Blood Loss and Iron Deficiency Iron is absorbed in the proximal small intestine and stored in spleen, liver, and bone marrow as ferritin (soluble and mobile) and hemosiderin (insoluble). Iron is transported in plasma by transferrin, which is normally 20% to 60% saturated with iron.

Answer 165

If external hemorrhage becomes chronic, iron deficiency may develop. Young animals are at greatest risk due to relatively small iron stores and large iron requirements during growth. Depending upon the magnitude of iron loss, the anemia may be regenerative or nonregenerative and may be characterized by microcytic normochromic to microcytic hypochromic indices. Marked anisocytosis may be present, and the RDW is increased. A pronounced reticulocytosis is usually found.

Answer 166

Thrombocytosis is a common finding in iron deficiency anemia. Other typical findings include mild to moderate hypoproteinemia, hypoferremia (may be normal or slightly elevated if the sample is hemolyzed, or if there was a recent transfusion), low transferrin saturation, decreased serum ferritin concentration (may be elevated in inflammatory conditions), normal to slightly elevated iron binding capacity, and depleted iron storage sites. Characteristic bone marrow findings include mild to moderate erythroid hyperplasia with nuclear distortion with no stainable iron (note that cats normally store little iron). Animals with severe iron deficiency are reported to have impaired intestinal absorption of iron, thus management is initiated with one injection of iron dextran. Supplementation is continued with oral ferrous sulfate; weeks to months of supplementation are usually required to correct the deficiency state. Whole blood or PRBC transfusions could put the animal at risk for volume overload, and should be used judiciously.

Answer 167

Platelets play a critical role in the initiation, regulation, and localization of hemostasis. The term primary hemostasis refers to the interactions among platelets, von Willebrand factor (VWF), and the vessel wall that culminate in the formation of a platelet plug. These reactions begin with platelet contact with the damaged vessel and VWF-mediated adhesion; proceed through platelet activation, degranulation, and aggregation; and conclude with the development of platelet-dependent procoagulant activity and clot retraction.

Answer 168

Platelet Physiology Megakaryocytic precursor cells in the bone marrow are programmed, through the action of transcription factors and thrombopoietin, to form platelet-specific organelles and to express platelet cell surface proteins. The entire megakaryocyte is converted into a mass of proplatelets that break away from the megakarcyote body and fragment into individual platelets. The platelets are released from the marrow and circulate in the vascular compartment as quiescent, nonadhesive, smooth disks. Approximately 100 billion platelets are released each day to maintain a peripheral platelet count of 200 million to 500 million cells per milliliter of blood.

Answer 169

1. In the initial step of activation, platelets rapidly transform into adhesive, spiny spheres capable of recognizing and binding to exposed matrix components of the subendothelium. Surface binding initiates cell-signaling pathways, which then mediate granule secretion. Granule contents include adenine nucleotides, calcium, serotonin, and adhesive proteins such as fibrinogen, VWF, fibronectin, and P-selectin. Secreted compounds accumulate locally, interact with their respective surface receptors, and recruit additional platelets to the site of injury. Large-order platelet aggregates then accumulate and bridge the zone of vascular damage to form a hemostatic plug. Thrombin cleavage of fibrinogen strengthens the platelet plug as a fibrin-platelet meshwork develops.

Answer 170

Late-stage platelet activation includes exposure of platelet membrane phosphatidylserine (PS) and the release of PS-rich microparticles, which act as scaffolding for the assembly of coagulation factor complexes. The expression of platelet procoagulant activity greatly amplifies local thrombin and fibrin generation. Contraction of platelet cytoskeletal proteins linked to platelet integrin receptors for fibrin and fibrinogen results in consolidation and subsequent retraction of the growing clot.

Answer 171

The endoperoxides prostacyclin (prostaglandin I2 [PGI2]), prostaglandin E2 (PGE2), and prostaglandin D2 (PGD2), which are synthesized by endothelial cells and released into the vascular space, serve as antagonist ligands that react with their respective platelet receptors to dampen platelet reactivity. (Figure 189-2).

Answer 172

Platelet integrins and nonintegrin glycoprotein receptors play a critical role in adhesion (platelet–subendothelial matrix interactions) and aggregation (platelet-platelet association). The αIIbβ3 complex (GPIIbIIIa) is the most abundant platelet integrin and functions as the activation-dependent receptor for fibrinogen, fibronectin, and VWF. Binding of fibrinogen to this receptor is essential for aggregation and clot retraction. Platelet adhesion to collagen and collagen-induced signaling are supported by collagen's interaction with the integrin receptor α2β1 (GPIaIIa).

Answer 173

Surface receptors, coupled to G proteins, span the platelet membrane and transmit signals induced by agonist binding. In platelets, Gq serves as this link for most agonists. Gq is coupled to phospholipase C, which in turn generates diacylglycerol (DAG) and inositol triphosphate, leading to calcium release from the endoplasmic reticulum; protein kinase C and myosin light chain kinase activation; and phosphorylation of platelet-signaling proteins. During activation, phospholipase A2 releases arachidonic acid from membrane phospholipids. Cyclooxygenase and thromboxane synthetase convert arachidonic acid to the potent agonist thromboxane A2 (see Figure 189-2).

Answer 174

Platelet–von Willebrand Factor Interaction Subendothelial collagen fibrils and bound VWF are exposed when the vascular endothelium is injured. The affinity and strength of the VWF-collagen bond is proportional to VWF multimer size. Collagen-bound VWF displays a conformational change that allows it to interact with the platelet GPIb/V/IX complex. As platelet GPIb contacts and engages with VWF, platelets slowly roll and become activated by interaction with collagen fibrils. VWF then binds to GPIIb/IIIa receptors exposed on the surface of activated platelets. Adhesion and aggregation at high shear rates depend on this VWF binding to activate platelet GPIIb/IIIa.

Answer 175

petechiae (pinpoint hemorrhage), ecchymoses (bruising), and mucosal hemorrhage, such as epistaxis, hematuria, gingival and intestinal hemorrhage, and prolonged bleeding after injury. These signs are suggestive of capillary and small vessel hemorrhage, but none are pathognomonic for a specific disease. For example, ecchymoses are often seen in association with thrombocytopenia but also may be signs of inflammatory vasculitis.

Answer 176

The initial assessment of any patient with signs of bleeding should aim to distinguish between hemorrhage from injured or diseased blood vessels and hemostatic failure. If the source or cause of hemorrhage cannot be readily identified, platelet count and coagulation screening tests should be performed early in the diagnostic workup. These tests can help both to detect a hemostatic defect and to guide the selection of appropriate ancillary diagnostic tests. The platelet count (per µL) can be estimated by counting the number of platelets in 10 oil immersion fields and multiplying the average number per field by 15,000 to 20,000. Either the activated clotting time (ACT) or point-of-care coagulation assays can be performed in-house to rule out clinically severe coagulation factor deficiencies.

Answer 177

Quantitative platelet defects are common hematologic abnormalities. Normal platelet numbers for dogs and cats range from approximately 200,000/µL to 500,000/µL. Each testing laboratory should provide species-specific reference ranges for their method. High or low platelet counts are found in many patients having systemic inflammatory and neoplastic diseases. Specific diagnostic tests (Table 189-2) are indicated for patients with moderate to severe thrombocytopenia or thrombocytosis, with associated clinical signs.

Answer 178

Thrombocytopenia rarely causes signs of abnormal hemostasis unless the platelet count falls below 50,000/µL, with petechiation and spontaneous hemorrhage most likely at counts below 20,000/µL. Clinical signs may appear at higher platelet counts, however, if the patient has a concurrent disease that further impairs hemostasis.

Answer 179

Impaired platelet production, Increased peripheral consumption or sequestration, and Immune-mediated destruction. In many disease syndromes, more than one mechanism is involved.

Answer 180

Production defects are likely in patients with thrombocytopenia combined with leukopenia and/or anemia. Immature platelets have a relatively high mean platelet volume (MPV) and ribonucleic acid (RNA) content, detected as “reticulated” platelets by thiazole orange staining.

Answer 181

The presence of reticulated platelets indicates ongoing platelet production, but their absence does not confirm megakaryocyte hypoplasia. Bone marrow examination, therefore, is the most accurate and direct means of evaluating megakaryopoiesis. Normal to high megakaryocyte numbers are typical of peripheral platelet consumption or destruction. Megakaryocyte hypoplasia confirms a platelet production defect and may reveal an infectious agent or abnormal cellular or stromal proliferation. In most cases, the combination of bone marrow examination, drug and travel history, and serology or polymerase chain reaction (PCR) testing to detect infectious agents leads to definitive diagnosis of production defects.

Answer 182

Splenic enlargement, for any reason, causes increased platelet sequestration and may result in thrombocytopenia with a shortened platelet lifespan. Increased peripheral platelet consumption accompanies systemic vasculitic disorders and disseminated intravascular coagulation (DIC). The primary means of diagnosing sequestration disorders include splenic and lymph node aspiration cytology, serology and biopsy to detect infectious agents and inflammatory disorders, and coagulation tests to define a DIC process.

Answer 183

Immune-mediated platelet destruction is common. Primary immune-mediated thrombocytopenia (IMT) implies an autoimmune disorder with production of antibodies directed against normal platelet antigens. Secondary IMT occurs in association with infection, drug therapy, neoplasia, polyimmune syndromes, or as a complication of platelet transfusion. In these patients, platelet-bound antibody may represent immune complexes, antibodies directed against neoantigens or foreign platelet antigens, or nonspecific binding.

Answer 184

The presence of antibodies on the surface of platelets (platelet-bound antibody) or antibodies in patient sera capable of binding normal platelets (platelet-bindable antibodies) can be detected with flow cytometry or enzyme-linked immunosorbent assay (ELISA). Flow cytometric assays configured to detect platelet-bound canine IgG have been developed for clinical use. The tests are generally sensitive, but they are nonspecific. Detection of platelet-bound IgG does not differentiate patients with primary IMT from those with secondary IMT, and nonspecific antibody binding may complicate interpretation of test results. Microthrombocytosis (MPV less than 5.5 fL) has been described as a feature of primary and secondary IMT and is seen early in the disease course. In a case review, severe thrombocytopenia (less than 20,000/µL) and microthrombocytosis were found almost exclusively in dogs with IMT; however, only half of the IMT patients had these abnormalities. Accurate MPV determination is affected by the anticoagulant used; platelets stored in ethylenediamine tetraacetic acid (EDTA) rather than citrate may have artifactual increases in MPV.

Answer 185

Chronic blood loss, Neoplasia, Systemic inflammatory disease, Hypercortisolism. High platelet counts may occur after splenectomy. A persistent and markedly high platelet count (greater than 900,000/µL) is suggestive of primary bone marrow disease (e.g., myelodysplasia, essential thrombocythemia) and is an indication for bone marrow examination. The clinical features of essential thrombocythemia in human beings and dogs include splenomegaly and hemorrhage caused by platelet dysfunction.

Answer 186

The buccal mucosa bleeding time (BMBT) is an in vivo screening test of primary hemostasis. If thrombocytopenia has been ruled out, a long BMBT is compatible with either platelet dysfunction or VWF deficiency. Platelet dysfunction is definitively diagnosed using more comprehensive tests of platelet structure and activation response. To ensure platelet viability, functional assays are best performed within 2 to 3 hours of sample collection. The PFA 100 (Dade Behring, Newark, Del.) can be used to measure platelet adhesion and aggregation with small volumes of whole blood (less than 2 mL) under conditions that simulate blood flow. More specific assessment of platelet function is performed by monitoring agonist-induced responses of shape change, aggregation, and release of dense granule contents

Answer 187

SPECIFIC PLATELET DISORDERS Thrombocytopenia Thrombocytopenia is the most common acquired hemostatic defect of dogs and cats. Many different pathogens cause thrombocytopenia, often through combined marrow suppression and an increased rate of peripheral loss. AArthropod-borne agents are increasingly identified as the cause of cytopenias in dogs and cats. Although dogs and cats with infectious thrombocytopenias may initially respond to steroid administration, sustained platelet response and disease resolution require specific treatment. Mild to moderate thrombocytopenia is seen in association with many tumor types, with more severe depression likely in hematopoietic neoplasia such as multiple myeloma, lymphoma, and leukemia. DIC is a common cause of thrombocytopenia in hemangiosarcoma, and tests to define a DIC process should be performed in any cancer patient with a falling or low platelet count. In addition to tumor-mediated thrombocytopenia, cancer patients are at risk of developing thrombocytopenia arising from cytotoxic drug therapy. A thorough drug history is indicated for any patient with thrombocytopenia, because numerous drugs have been reported to impair platelet production, induce secondary immune destruction, and/or cause platelet dysfunction Establishing the causality of drug-induced thrombocytopenia is difficult, but ancillary diagnostics can help define possible underlying mechanisms. Numerous drugs have been reported to impair platelet production, induce secondary immune destruction, and/or cause platelet dysfunction Establishing the causality of drug-induced thrombocytopenia is difficult, but ancillary diagnostics can help define possible underlying mechanisms. The findings of pancytopenia and megakaryocytic hypoplasia indicate bone marrow suppression, and the presence of platelet-bound antibody is compatible with an immune-mediated process.

Answer 188

Idiopathic, or primary, IMT is an autoimmune disease, usually mediated by IgG directed against platelet membrane GPIIbIIIa. The disease is uncommon in cats, but in case reviews of canine thrombocytopenia, primary IMT accounts for approximately 5% to 15% of patients, with overrepresentation of females and certain breeds (Cocker Spaniels, Poodles, and Old English Sheepdogs).

Answer 189

Combined clinical and laboratory criteria: exclusion of other underlying disease processes, the presence of severe thrombocytopenia (less than 50,000/µL), normal to increased megakaryopoiesis, microthrombocytosis, platelet-bound antibodies, and response to immunosuppressive therapy. Breed-specific, clinically asymptomatic thrombocytopenias occur in dogs. Healthy Greyhounds have a platelet count somewhat lower than that of other breeds, with a mean platelet count of approximately 150,000/µL. Cavalier King Charles Spaniels have a hereditary macrothrombocytopenia associated with a beta-tubulin defect. Affected dogs have platelet counts ranging from 25,000/µL to 100,000/µL.

Answer 190

Acquired Platelet Dysfunction The antiplatelet effects of aspirin are caused by a well-characterized, irreversible inactivation of intraplatelet cyclooxygenase (COX). Other nonsteroidal antiinflammatory drugs (NSAIDs) cause transient COX inhibition, and newer NSAIDs that selectively inhibit the COX-2 isoform are predicted to have fewer antiplatelet effects.

Answer 191

Hereditary platelet function defects (thrombopathias) are rare but likely are underdiagnosed because of logistic difficulties in performing platelet function studies. Diseases are broadly grouped as defects of membrane glycoproteins, storage granules, signal transduction, or procoagulant activity. Defects in the GPIIbIIIa complex, referred to as thrombasthenic thrombasthenia, have been identified in otter hounds and Great Pyrenees as the result of two distinct GPIIb mutations. It is likely that the platelet function defects found in unrelated breeds are caused by unique mutations.

Answer 192

Type 1 VWD, the most common form, is typically a mild to moderate bleeding diathesis characterized by low plasma VWF:Ag and normal multimer distribution. Type 2 VWD is a moderate to severe bleeding diathesis with a variable reduction in VWF:Ag and a disproportionate loss of high–molecular weight (HMW) multimers. Type 3 VWD is a severe bleeding disorder caused by a total lack of VWF.

Answer 193

A normal platelet count, Normal coagulation panel, Long BMBT, Long PFA closure time, Definitive diagnosis confirmed by the finding of low plasma VWF:Ag. Comprehensive analyses for VWD subtype classification include quantitative, functional, and qualitative VWF assays

Answer 194

Expression of type 1 VWD is complex, with evidence for both incomplete dominant and recessive patterns. Type 1 VWD is common in Doberman Pinschers, and in this breed clinical signs of VWD are typically seen in dogs with a VWF:Ag of 15% or lower. The clinical severity of type 1 VWD for an individual dog (or human patient) cannot be explained fully by current molecular or biochemical tests. Risk of hemorrhage represents a continuum, with severe signs typically associated with relatively severe reduction in plasma VWF concentration. In contrast, type 2 and type 3 VWD in dogs appear to be simple recessive traits. Clinically affected dogs inherit a mutant VWF gene from each parent and express a bleeding tendency. The carrier parents are clinically normal, although their plasma VWF is typically low (less than 50% VWF:Ag). Mutations causative for type 3 VWD have been described in Scottish Terriers and Dutch Kooiker Dogs.

Answer 195

Effective management of platelet disorders and VWD requires control of active sites of bleeding, stabilization of the patient to reverse signs of blood loss anemia and hypovolemia, and identification and correction of the primary disease that caused or exacerbated the hemostatic defect. Initial treatment modalities include both nontransfusion and transfusion support. Although the BMBT is a useful screening test of primary hemostasis for diagnostic purposes, it is not an accurate predictor of disease severity or surgical hemostasis.

Answer 196

Based on the geographic location, history, and initial workup, institution of appropriate therapy for infectious thrombocytopenia (e.g., doxycycline for Ehrlichia, Rickettsia, and Haemobartonella spp.) is indicated pending confirmatory test results. Immunosuppressive doses of prednisone are administered if the diagnostic workup indicates that primary IMT is likely. Primary IMT patients usually demonstrate resolution of petechiae and an increased platelet count within 2 to 5 days of starting therapy. Refractory primary IMT can be effectively treated with vincristine. Immunosuppressive therapy for IMT can be considered successful if a stable platelet count (preferably at or above 100,000/µL) is attained. Maintenance involves slow, gradual tapering of immunosuppressive therapy, with minimal exposure to unnecessary drugs, vaccination, or stress conditions to avoid relapse.

Answer 197

Desmopressin acetate (DDAVP; deamino 8 D-arginine vasopressin) is a synthetic vasopressin analog used in human medicine to treat a variety of hemostatic defects, including acquired platelet function defects and mild VWD. Desmopressin has been reported to shorten the BMBT and the PFA-100 closure time and to provide surgical hemostasis when administered 30 minutes before surgery to Doberman Pinschers with type 1 VWD. Desmopressin therapy could be considered for other mild to moderate acquired or hereditary platelet function defects. Close monitoring to determine the extent and duration of response is required, and transfusion should be available if the response to desmopressin is inadequate.

Answer 198

Transfusion solely to supply platelets (see Table 189-9) is rarely indicated or beneficial for thrombocytopenic patients or those with acquired platelet function defects. The survival of transfused platelets in IMT patients may be less than 1 day, which further limits their clinical utility. Platelet transfusions should be considered, however, in patients with persistent and uncontrolled bleeding or signs of central nervous system hemorrhage. Dogs and cats affected with severe hereditary thrombopathias may benefit from platelet transfusion as prophylaxis for surgery or if they develop severe spontaneous bleeding.

Answer 199

Fresh whole blood, as platelet replacement, must be maintained at room temperature, collected in a citrate-based anticoagulant, and transfused as soon as possible after collection. This product is best used for patients with active bleeding or when no other platelet product is available.

Answer 200

Platelet-rich plasma (PRP) is prepared by centrifugation of whole blood at low G force within 6 hours of collection. The expected platelet yield is approximately 80% of the platelets, in one-third volume, of the starting whole blood unit. In accordance with human blood banking standards, units of PRP, prepared from 450-mL units of whole blood, are expected to contain at least 50 billion platelets.[50] Low-volume platelet concentrates (PC) are prepared from PRP by a second centrifugation step. Platelet-rich plasma and PC must be maintained at room temperature from the time of collection until transfusion, with administration as soon as possible after collection, and maximum storage of 3 days.

Answer 201

Preliminary studies of dimethylsulfoxide (DMSO) cryopreserved canine platelet concentrates have been published recently and a commercial product is available. This product may widen the availability of platelet transfusion beyond referral centers capable of producing components in-house. Strict attention to aseptic technique is critical during collection and transfusion of platelet products to prevent contamination or disease transmission.

Answer 202

Plasma components are the safest and most effective products for treating VWD. Plasma cryoprecipitate is prepared from fresh frozen plasma (FFP) and contains a fivefold to tenfold concentration of active VWF in approximately one-tenth volume of the starting plasma. Cryoprecipitate is the best product for rapid replacement of VWF, but fresh frozen plasma is an acceptable alternative if cryoprecipitate is unavailable. The use of plasma components rather than whole blood prevents sensitization to red cell antigens, eliminates the need for canine type-matched donors, and minimizes the risk of volume overload.

Answer 203

A single definition is lacking. Veterinary patients with SLE classically demonstrate at least two separate manifestations of autoimmunity in addition to the presence of antinuclear antibody (ANA). However, some patients demonstrate clinical features of multisystemic autoimmunity yet lack serum ANA.

Answer 204

Autoimmune disease may be defined as a clinical syndrome caused by the activation of T cells or B cells, or both, in the absence of an ongoing infection or other discernible cause.

Answer 205

1. tissue damage (type III hypersensitivity); however, 2. direct antibody-mediated cytotoxicity (type II hypersensitivity) and 3. cell-mediated autoimmunity (type IV hypersensitivity) also occur.

Answer 206

1. Pathogenic antibodies: SLE patients produce antibodies directed against a broad range of nuclear, cytoplasmic, and cell membrane molecules. Autoantibodies may cause damage through the formation of immune complexes, opsonization of target cells, and interference with cellular physiology. Antibodies may penetrate living cells and bind to cytoplasmic or nuclear structures, alter cell function, and contribute to disease by mechanisms other than classic complement-mediated injury. 2. Pathogenic immune complexes: Immune complexes, formed every time antibody meets antigen, are normally removed by the mononuclear phagocyte system. When there is continued production of autoantibody to a self-antigen, overload of the mononuclear phagocyte system may occur. Circulating immune complexes will deposit in walls of blood vessels where there is physiologic outflow of fluid, such as glomeruli, synovia, and choroid plexus. Some immune complexes are “tissue tropic” and prone to bind in tissues because of cationic charge or because the antibodies they contain are directed against tissue components. Trapped immune complexes activate complement, attracted neutrophils will release lysosomal enzymes, and tissue damage is caused.[2] 3. Autoreactive T cells: T cells may directly cause tissue damage in SLE. Dermatologic lesions, polymyositis, and vasculitis have been associated with cytotoxic T cell–mediated damage

Answer 207

In dogs SLE is clearly inherited and experimental colonies of dogs with SLE have been established. SLE in dogs has been associated with the allele dog leukocyte antigen (DLA) A7, along with a negative (or “protective”) association with DLA A1 and B5. Dogs with a specific allotype of the fourth component of complement may be predisposed to SLE as well as dogs with decreased serum IgA. SLE may occur more frequently in purebred cats, also suggesting genetic influence.

Answer 208

1. Enviromental factors (UV light) 2. Sex (people, not dogs?) 3. Drugs: Propylthiouracil has been associated with hemolytic anemia, thrombocytopenia, and development of ANA in cats. Methimazole has been associated with development of ANA in cats, but clinical signs of SLE have not been reported. Hydralazine has been associated with development of ANA in the dog. 4. Infectious agents? (In cats the viruses feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) can induce disease similar to SLE, and serum ANA may occur in the early stages of FeLV infection. Whether FeLV- or FIV-induced disease is truly similar to SLE is debated. Feline ehrlichial disease has also been associated with positive ANA)

Answer 209

1.Nonerosive polyarthropathy is the most frequent primary complaint in dogs. Synovial fluid analysis reveals neutrophilic inflammation. 2. Fever is frequently reported in both dogs and cats and may be either persistent or intermittent. 3. In humans, the kidney is commonly involved, with biopsy demonstrating involvement in almost all SLE patients. . In dogs and cats, proteinuria and glomerular lesions are also frequent. 4. Cutaneous manifestations in dogs may include erythema, scaling, crusting, depigmentation, and alopecia. Lesions may develop in the skin, mucocutaneous junctions, and oral cavity. Biopsy reveals inflammatory infiltrates 5. In dogs, although it is common to find anemia of chronic inflammation, Coombs-positive anemia is uncommon. Thrombocytopenia may be severe enough to cause bleeding. Leukopenia has been frequently reported. As in dogs, hemolytic anemia is uncommon in cats and thrombocytopenia rare. 6. In animals, subtle behavioral disturbances (as seen in people) may go unrecognized. 7. Polymyositis, Polyneuritis 8. Neutrophilic myocarditis

Answer 210

The most common syndrome recognized in the dog is: 1. immune-mediated polyarthritis, in combination with 2. immune-mediated skin disease, 3. glomerulonephritis, 4. hemolytic anemia, or 5. thrombocytopenia. Similar signs occur in the cat; however, neurologic signs may be more common.

Answer 211

Diagnostic testing of suspected SLE patients should include hematology, biochemistry, urinalysis, imaging, joint fluid cytology, histopathology of the skin and/or kidney, and serum ANA. Cats should be tested for FeLV and FIV. Infectious and neoplastic disease must be excluded through imaging, culture of urine, blood and/or joint fluid, serology for tick-borne and fungal disease, and therapeutic antibiotic trials. Immunodiagnostic investigations may include Coombs’ testing, platelet autoantibodies, rheumatoid factor, coagulation testing for antiphospholipid antibodies, serum immunoglobulin, complement, circulating immune complex concentrations, and endocrine autoantibodies (i.e., thyroglobulin). Immunohistologic investigation may include immunoperoxidase and immunofluorescence staining and electron microscopic evaluation. Biopsies may be supportive but are rarely diagnostic of SLE by themselves. When the skin is biopsied, care should be taken to avoid ulcers or erosions, since an intact epidermis is necessary to substantiate the diagnosis. Oral biopsy specimens are rarely beneficial, since ulcers, which are inherently not diagnostic, are common in this location. Erythematous areas adjacent to ulcers yield the most diagnostic results. The diagnosis of SLE in cats is less well defined. In some studies all cats with positive ANA test results were diagnosed with SLE, but whether these patients truly had SLE is debatable. Another unanswered question is how to categorize FeLV- or FIV-positive patients. Some reports include FeLV-positive cats while others exclude them. Because of the possibility of ehrlichial disease, it has been recommended that all cats receive a course of doxycycline before the diagnosis of immune-mediated disease is made.

Answer 212

A lupus erythematosus (LE) cell is recognized as a neutrophil that contains phagocytized nuclear material. Because of technical, sensitivity, and specificity problems, the LE cell test has been largely replaced by the more sensitive ANA test. LE cells may rarely be seen on smears of pericardial, pleural, peritoneal, joint, cerebrospinal, and blister fluid and when present are highly suggestive of SLE.

Answer 213

Antinuclear antibodies are a heterogeneous population of antibodies directed against various nuclear antigens. ANA may be detected using frozen sections of rat liver or cultured cell lines. The result of an ANA test is commonly reported as a serum titer and, sometimes, pattern of nuclear staining. The most commonly observed patterns are speckled or homogenous staining, but there is no clear association between patterns and the nature of clinical disease. A clinically significant titer must be distinguished from low ANA titers that may be present in up to 10% of normal animals and animals with any chronic inflammatory, infectious or neoplastic disease. The most appropriate substrate, conjugate, and methodology for ANA testing remains undefined and each laboratory's value should be interpreted individually. ANA-negative SLE cases have been described in veterinary patients,[and a positive ANA should be neither required nor sufficient in itself to make a diagnosis of SLE. SLE should not be diagnosed or excluded based upon this single test result.

Answer 214

MANAGEMENT: Sunlight should be avoided if photosensitization occurs. Most patients also require corticosteroid administration. A combination of prednisone and immunosuppressants is recommended in more severe cases, especially those affecting the kidneys. Full doses are administered until the disease is in complete remission, defined as resolution of clinical signs as well as radiographic or laboratory changes that were initially present. After remission is attained the dose is tapered, generally in half, for approximately 4 weeks. Some cats do not respond to prednisone. Cats that do not completely respond to prednisone should be treated with an alternate steroid (prednisolone, methylprednisolone, triamcinolone, or dexamethasone) prior to instituting additional immunosuppressant therapies. Combination immunosuppression therapy allows a lower dose of corticosteroid to be used. Azathioprine (Imuran) is the drug most frequently used in dogs. Azathioprine is not recommended for use in cats. Instead, chlorambucil may be administered along with corticosteroids for cats that require additional immunosuppression. Chlorambucil (Leukeran) is used in cats. Potential side effects include anorexia and bone marrow suppression. In cats, the dosage of chlorambucil should be tapered before the prednisone is tapered. Alternative immunosuppressants may include cyclosporine. Immunoglobulin G may be useful of refractory cases. Novel therapeutic approaches include prednisone combined with levamisole.

Answer 215

hemolysis, hemorrhage, [erythroid] hypoplasia, hemodilution (4 Hs);' One or more may be involved in a case.

Answer 216

Hemolytic and hemorrhagic anemias may be either regenerative (most frequent occurrence) or nonregenerative, while hypoplastic anemia is, by definition, nonregenerative.

Answer 217

Anemia is also classified by duration as acute or chronic, but there is a spectrum in between the two. Acute anemias are caused by either hemolysis or hemorrhage, while chronic anemias may be caused by hemolysis, hemorrhage, or hypoplasia.

Answer 218

Because of the shorter red cell lifespan of cats (.....days vs. ........days for most dog breeds), erythroid hypoplasia will cause anemia sooner in cats than in dogs. This is compensated for by the ability of cats to tolerate more severe chronic anemia than dogs.

Answer 219

Hemodilution will lower hematocrit (Hct), hemoglobin (Hb), and red cell count, but does not cause a true anemia as there is no decrease in red cell mass. Dilutional pseudoanemia may occur with fluid therapy and physiologic states that cause plasma volume expansion.

Answer 220

The signs of anemia are related to its severity and duration. Animals with moderate to severe acute anemia will be weak and inappetent. Many nonregenerative anemias are chronic, and animals may have minimal weakness and inappetence because of mechanisms that alleviate tissue hypoxia to compensate for decreased Hb concentration. These compensatory mechanisms are hemodynamic and nonhemodynamic. The principle nonhemodynamic mechanism is increased synthesis of 2,3-DPG, which decreases the affinity of Hb for oxygen, facilitating oxygen release to tissues. This mechanism is present in dogs but not cats. Feline Hb normally has reduced affinity for oxygen, which permits cats to tolerate more severe anemia than dogs.

Answer 221

The main hemodynamic compensatory mechanism is increased cardiac output, which is due to decreased afterload, increased preload, increased contractility, and increased heart rate.

Answer 222

Decreased afterload is due to nitric oxide–mediated vasodilation, because Hb, a potent binder of nitric oxide, is low. Lower blood viscosity is also a factor in decreased afterload. Increased preload is due to salt and water retention, which may be secondary to the low systemic vascular resistance.

Answer 223

Sympathetic nervous system activation contributes to increased heart rate and contractility. In animals with acute anemia, the hemodynamic changes are manifested as tachycardia and increased pulse strength. As anemia becomes more chronic, heart rate and pulse strength become more normal. However, the chronic volume overload results in cardiac eccentric hypertrophy. Workup of an animal with severe chronic anemia may thus identify cardiomegaly, pleural effusion and ascites, representing a state of “high-output heart failure.” Although signs of right-sided heart failure are more common, pulmonary edema may also occur. These signs should not be confused with typical low-output congestive heart failure which may also result in pale mucous membranes (see Chapter 71).

Answer 224

Anemic cardiomyopathy does not typically cause arrhythmias. Dogs with Hct

Answer 225

Cats with severe chronic anemia may develop multifocal retinal bleeding, affecting both the tapetal and nontapetal funds. Vision is usually not affected, and most changes are reversible, but rarely a case may progress to partial or complete retinal detachment which may be permanent. Although the hemorrhages of anemic retinopathy may resemble those of hypertensive retinopathy, hypertension is not the mechanism. Cats with severe chronic anemia are normotensive or hypotensive. Anemic retinopathy has been reported with both acute and chronic anemia in humans, but not in dogs. The mechanism of retinopathy is not known, but it is suggested that tissue hypoxia leads to retinal vasodilation and leakage, as occurs in other tissues. Retinal changes in an anemic cat should not be used as presumptive evidence for the presence of renal failure or feline leukemia virus (FeLV) infection.

Answer 226

Treatment: Increasing red cell mass. In dogs and cats this is most often accomplished by red cell transfusion, as discussed in Chapter 142. Transfusion should be given regardless of cause if the anemia is causing clinical signs, unless there are specific contraindications or if the animal is stable and very rapid regeneration is anticipated.

Answer 227

The altered hemodynamic state in anemia has important therapeutic implications. While the lowering of the Hct with fluid therapy in anemia is not usually a concern because the existing red cell mass is not being decreased, an anemic animal is at increased risk for volume overload and fluid congestion. Dogs with immune-mediated hemolytic anemia (IMHA) frequently develop ascites and pleural effusion after several days of fluid therapy. (This has also been suggested to be due to a vasculopathy accompanying the systemic inflammatory response.) Volume overload is a particular concern in animals with chronic anemia, and fluid therapy and transfusions should be given slowly to these patients. Packed red cells are preferred to whole blood. Particular care must be taken when administering Oxyglobin (Biopure Corporation, Cambridge, Mass.), especially in cats, because of its colloidal volume expanding and nitric oxide scavenging effects. It also has a short duration of action that limits its benefit in chronic anemia. Recombinant human erythropoietin (rhEPO) was initially used in humans to treat anemia due to kidney disease, but it is widely used now as an alternative to allogeneic transfusion in oncology, critical care, and surgery.[19-22] Other than in chronic renal failure, rhEPO has not had extensive use in dogs in cats

Answer 228

Detection, Delay, Destruction, Deficiency, Deep-Development-Dam, Diversion, Displacement, Depression, Dilution, and Drugs. The categories are not mutually exclusive.

Answer 229

While there are numerous causes of nonregenerative anemia, a pathophysiologic mechanism common in many is defective development of erythroid cells in the bone marrow, or dyserythropoiesis. On microscopic examination of a bone marrow biopsy, this may be manifested as ineffective erythropoiesis or maturation arrest, characterized by presence or expansion of early erythroid series (e.g., rubriblasts) and absence of later series (e.g., metarubricytes). This may be due to arrested development and/or shortened lifespan in the bone marrow. Another common, often concurrent, finding is dysplasia (abnormal appearance) of erythroid cells, i.e., erythrodysplasia. a.

Answer 230

Dysplastic bone marrow cell morphology includes abnormal nuclear features (abnormal size, fragmentation, lobulation, pyknosis, multiple nuclei), abnormal cytoplasmic features (abnormally large size and inclusions), and nuclear-cytoplasmic maturation asynchrony. Similarly, dyshematopoiesis refers to defective blood cell formation in two or more lineages (i.e., red cell, platelets, or granulocytes). (Dysmyelopoiesis has been used synonymously with dyshematopoiesis, and in a more restricted sense to refer to abnormal granulocyte development,which is how it will be used here.)

Answer 231

Myelodysplasia refers to dysplastic changes in two or more lineages; it may also refer to myelodysplastic syndrome (MDS), which is a group of premalignant to malignant clonal disorders that are discussed later in this chapter. To avoid confusion, in this chapter myelodysplasia is used only in its morphologic sense to refer to any dysplastic changes. Myelodysplasia has a similar appearance regardless of etiology, and it is also emphasized that bone marrow dysplastic and neoplastic changes may have very similar appearances.

Answer 232

Quantification of polychromasia is less precise than reticulocyte counting and also mildly underestimates regeneration, so the latter is recommended to confirm poor regeneration, especially in borderline cases. Increases in mean cell volume (MCV) and red cell distribution width (RDW) support the presence of regeneration

Answer 233

In cats, an increase in punctate reticulocytes will help identify a previous or ongoing regenerative response. Enumeration of punctate reticulocytes has not been standardized.

Answer 234

Identification of abnormalities associated with hemorrhage or hemolysis may facilitate the diagnosis of regenerative versus nonregenerative anemia. A bone marrow biopsy may be necessary to look for erythroid hyperplasia.

Answer 235

Many “nonregenerative” anemias are actually hyporegenerative, where a regenerative response is present, but it is inappropriately low for the degree of anemia. If this is not recognized then complicating factors limiting erythropoiesis and contributing to the anemia may be overlooked. As the anemia becomes more chronic and the regenerative response becomes less intense, it becomes more difficult to judge the adequacy of regeneration.

Answer 236

The more common causes in the dog, where acute anemia substantially contributes to the salient presenting clinical signs, include IMHA, babesiosis, hemotropic mycoplasma infection, and internal hemorrhage due to vitamin K antagonist poisoning or ruptured splenic hemangiosarcoma. Causes in the cat include hemotropic mycoplasma infection and cytauxzoonosis. Distinguishing an acute preregenerative anemia from a chronic nonregenerative one becomes more difficult as the anemia becomes less severe. Fortunately the clinical urgency also becomes less, and serial hemograms may be followed to observe for regeneration. If necessary, a bone marrow biopsy may be used to examine for erythroid hyperplasia.

Answer 237

Cytotoxic drugs used to treat neoplastic and immune-mediated diseases kill mitotically active cells and thereby cause transient injury to various bone marrow progenitor cell compartments. This also occurs with autumn crocus poisoning due to colchicine, and total and half-body irradiation have a similar effect. The result is predictable, dose-dependent, transient trilineage hypoplasia in the bone marrow, and pancytopenia in the peripheral blood. The changes in peripheral blood are a reflection of mature cell lifespan. The lifespan of neutrophils is several days and the half-life in blood is several hours, while the mean lifespan of platelets in dogs is 5.5 to 6.5 days.

Answer 238

Following acute bone marrow injury, neutropenia appears prior to, and is more severe than, thrombocytopenia, which in turn appears prior to, and is more severe than, anemia.

Answer 239

Animals with cytotoxic myelosuppression will be presented for lethargy and fever due to infection secondary to neutropenia. Anemia associated with the chemotherapy protocols commonly used in veterinary medicine is usually marginal to mild in dogs, while cats may develop more severe anemia. The anemia is initially normocytic normochromic, but later some macrocytosis and anisocytosis may develop reflecting regeneration. Unexplained transient myelosuppression occurs occasionally, and it is assumed in such cases that the bone marrow received an unidentified toxic insult. If bone marrow biopsy is obtained during bone marrow recovery, an exuberant response predating the rise in mature myeloid and peripheral blood cell counts may be mistaken for leukemia, as the latter may occur without abnormal peripheral blood cells (“aleukemic leukemia”). Early myeloid hyperplasia is characterized by proliferation of genetically normal blast cells while myeloid leukemia is characterized by proliferation of mutant blast cells. Distinguishing the two populations morphologically is difficult, and serial hemograms and bone marrow biopsies may be necessary to confirm a diagnosis.

Answer 240

All forms of estrogen may cause bone marrow hypoplasia in dogs, but individual dog susceptibility varies and older dogs are at increased risk. Estrogen toxicosis does not occur with the use of [diethyl]stilbestrol at standard recommended doses for urinary incontinence and vaginal discharge, but may occur at higher doses. Currently the most common cause is probably Sertoli cell tumor of the testicle. Feminization is more common than, and does not correlate with, pancytopenia, possibly because the former may occur with a lower testosterone : estradiol ratio without absolute increase in estradiol. Estrogen production and hematologic disorders may also occur with Leydig (interstitial) cell tumors. Sertoli and Leydig cell tumors have been reported in neutered male dogs, but none have had hematologic disturbances. Ovarian cysts and tumors in female dogs may produce estrogen but hematologic disturbances are rare.

Answer 241

The initial bone marrow response to estrogen intoxication is myeloid hyperplasia resulting in neutrophilia, followed by trilineage hypoplasia and pancytopenia. Bone marrow mast cell hyperplasia may also occur. By the time neutropenia occurs, the normocytic normochromic anemia is more severe than with myelosuppression due to cytotoxic drugs. There is evidence that estrogens are not directly toxic but that toxicosis is mediated by a secondary factor, perhaps of thymic origin.

Answer 242

managing neutropenic sepsis with antibiotics, thrombocytopenic bleeding with platelet transfusions, and anemia with red cell transfusions (see Chapter 142). Use of human recombinant human granulocyte-colony stimulating factor and rhEPO at standard doses may be beneficial, with a planned initial treatment period of less than 2 weeks to minimize risk of antibody formation. Cyclosporine may be considered in an effort to retard antibody formation if prolonged treatment is needed. Following estrogen withdrawal the bone marrow will probably recover in all cases, but providing adequate supportive care during potentially prolonged pancytopenia may be problematic. Cats are more sensitive to estrogen toxicosis than dogs, but exposure is rare and they do not develop bone marrow hypoplasia; fatality is due to liver disease.

Answer 243

Canine and feline parvoviruses damage intestinal crypt cells with issuant diarrhea and sepsis. The viruses are also cytopathic to myeloid and erythroid bone marrow progenitor cells and may cause dysplastic changes. The salient hematologic findings are neutropenia and lymphopenia. Anemia, if present, is usually mild and may be masked by dehydration. Anemia is likely due to blood loss, malnutrition, and erythroid infection.

Answer 244

Ehrlichia canis infection in dogs may cause monocytopenia to pancytopenia with bone marrow hyperplasia in the acute phase and hypoplasia in the chronic phase (see Chapter 206). Other potential bone marrow biopsy findings include plasma cell and mast cell hyperplasia. The mechanisms of hypoplasia are not known, but early progenitor cell infection has been shown with E. ewingii, and E. chaffeensis is cytopathic to bone marrow cells.

Answer 245

Bone marrow necrosis is believed to arise from vascular occlusion of small blood vessels and may lead to myelofibrosis. It has been seen with a number of infectious, immunologic, and neoplastic diseases and with various drugs. Idiopathic bone marrow necrosis in dogs has been characterized by hypo– to hyper–bone marrow cellularity and anemia with or without neutropenia and thrombocytopenia.

Answer 246

Iron deficiency increasingly limits regeneration. Iron deficiency in kittens (and probably in puppies) occurs with an iron-deficient all-milk diet and this contributes to the normal transient drop in Hct. Iron deficiency in a mature dog or cat is due to chronic blood loss. Causes include severe flea infestation, chronic hematuria, and chronic gastrointestinal bleeding, most commonly due to a tumor. It is important to note with the latter that vomiting and diarrhea may not be present, especially in cats, where weight loss and other nonspecific signs predominate.

Answer 247

Anemia in iron deficiency patients is initially regenerative, but over time regeneration wanes and becomes inappropriately low. The anemia is microcytic and hypochromic; in cats microcytosis is more difficult to detect and hypochromasia is often not present. Red cells swell during storage in EDTA, so ideally MCV should be measured on the day of collection. Microcytosis develops because metarubricytes stay in the bone marrow longer, undergoing an additional cell division, while awaiting completion of Hb synthesis. As the name implies, MCV is an average value, and the initial drop in MCV is within normal range as the percentage of microcytes increases.

Answer 248

There is a concomitant increase in RDW because of microcytosis and regeneration; examination of volume erythrograms may be used as an aid to detect microcytosis. The MCV continues to decrease to below reference range, at which point mean corpuscular hemoglobin (MCH) is usually low. The last red cell index to drop is mean corpuscular hemoglobin concentration (MCHC).

Answer 249

Red cell fragmentation/poikilocytosis and thrombocytosis are often present. Iron deficiency is further supported by documenting low to low-normal total serum iron, and high-normal to elevated transferrin (total iron-binding capacity) with low saturation. Serum iron and transferrin are measurable in most reference laboratories but the inexact and broad reference ranges for dogs and cats may make interpretation difficult. Serum ferritin is more reliable, and should be low-normal to low, but must be measured by a validated species-specific assay and is less available. Reticulocyte Hb content, reticulocyte MCV and other reticulocyte indices measured with the Advia 120 Hematology System (Siemens Healthcare Diagnostics) are more sensitive for iron deficiency than red cell indices and will likely be used with increasing frequency

Answer 250

Bone marrow biopsy will reveal erythroid hyperplasia, with presence or expansion of late erythroid series (rubricytes, metarubricytes), often megakaryocytic hyperplasia, and absence of storage iron in dogs. Iron is stored either as ferritin, which is soluble and mobile, or as hemosiderin, which is an insoluble aggregate that is less readily available to the body. Cats do not normally store iron in the bone marrow.

Answer 251

Correcting the underlying disorder, correcting the anemia, and correcting the iron deficiency. Transfusion with packed red cells, in addition to ameliorating the anemia, will provide an immediately available source of iron to the bone marrow. Following transfusion, improved regeneration will be seen within several days as the hyperplastic erythropoietic tissue thrives on the sudden influx of iron. Iron supplementation should then be given orally with ferrous sulfate or by injection with iron-dextran at the same doses used with rhEPO in chronic renal failure (see Chapter 311). The concentration of iron in preparations of ferrous sulfate may necessitate administration of inconveniently large volumes in cats.

Answer 252

2 to 6 months.

Answer 253

Anemia of inflammatory disease (disorder of iron sequestration) Chronic liver diseases, Sideroblastic anemia, Lead poisoning Copper deficiency

Answer 254

Chronic liver diseases, especially portosystemic shunts, may cause microcytosis, and occasionally hypochromia, in both dogs and cats due to defects in iron metabolism. Animals are usually presented for clinical signs of liver dysfunction; occasionally an incidental finding of a low MCV in an asymptomatic animal prompts diagnostic investigation. Bone marrow changes with portosystemic shunts are unremarkable.

Answer 255

Sideroblastic anemia is characterized by iron (sider in Greek) deposits in mature red cells (siderocytes) in blood and in nucleated red cells (sideroblasts) in bone marrow. It is a result of a defect in Hb synthesis. Acquired sideroblastic anemia in humans is most often a feature of MDS and this has been seen in cats. In a report of 7 dogs sideroblastic anemia was normocytic-microcytic, normochromic-hypochromic, and was associated with inflammation.

Answer 256

Dogs and cats with acute lead poisoning present with depression, anorexia, and neurologic and gastrointestinal signs. Animals are not anemic, but nucleated RBCs with or without basophilic stippling are often present in dogs, but only occasionally in cats. Although acute lead poisoning does not cause anemia, chronic poisoning in humans may cause a microcytic hypochromic anemia because lead interferes with the incorporation of iron into Hb. Lead has this effect in dogs, but in two studies of experimental chronic poisoning in dogs, microcytosis did not develop, perhaps because the treatment period (13 weeks) was not sufficiently long. Bone marrow changes in lead poisoning include erythroid hyperplasia with increasing number of metarubricytes and myeloid hyperplasia.

Answer 257

Copper deficiency may also cause a microcytic hypochromic anemia in humans and dogs, but bone marrow biopsy will reveal iron stores. Copper and zinc metabolism are related, and copper-deficiency anemia in humans and dogs may result from either a copper-deficient diet and/or chronic zinc intoxication. (Acute zinc intoxication causes hemolysis.) Copper deficiency in mature dogs has been seen with copper-chelation therapy and combined chronic copper and zinc intoxication. Bull terriers with lethal acrodermatitis are copper deficient. Anemia is not part of the disorder, perhaps because of concurrent zinc deficiency. Copper deficiency has not been reported in cats.

Answer 258

Microcytosis, sometimes associated with a slightly decreased Hct and MCHC, is a normal finding in Akitas and Shiba Inus

Answer 259

Metabolism of folate (folic acid) and of cobalamin (vitamin B12) is intricately related, and deficiency of one or both may cause megaloblastic anemia by interfering with DNA synthesis, which delays cell division.

Answer 260

The term megaloblastic anemia refers to dyserythropoiesis characterized by erythroid hyperplasia and dysplasia, with abnormally large normoblasts (prorubricytes and rubricytes), reflecting delayed nuclear maturation and cell division. The megaloblastic cells are fragile and may be destroyed in the bone marrow, with the resultant ineffective erythropoiesis leading to anemia. Some of the megaloblasts escape destruction and are released in the circulation as macrocytes, resulting in a progressive increase in MCV. Dysplastic changes also occur in other cell lines.

Answer 261

The most common cause of folate deficiency in humans is dietary deficiency, and folate requirements are increased during pregnancy. Other causes include tropical sprue (a disorder of intestinal malabsorption), and treatment with azathioprine, methotrexate, and other drugs that impair folate metabolism. In contrast to folate, cobalamin deficiency in humans is usually due to impaired absorption, a leading cause being of lack of production of intrinsic factor from the stomach, resulting in pernicious anemia. Cobalamin deficiency results in elevated blood levels of methylmalonic acid and homocysteine. Folate and/or cobalamin deficiency affects other organs, in particular the gastrointestinal tract and nervous system, and associated signs as well as overall well-being may be affected without overt hematologic changes.

Answer 262

Naturally occurring dietary folate and cobalamin deficiency has not been reported in dogs, and dogs are resistant to experimental folate deficiency. Serum folate declines in dogs during pregnancy, and supplementation has been associated with a reduction in congenital defects. In cats, naturally occurring megaloblastic anemia responding to folate and cobalamin supplementation has been reported infrequently, and megaloblastic anemia has occurred in experimental dietary folate deficiency. The anemia is normocytic to macrocytic.

Answer 263

Serum levels of folate and/or cobalamin may be reduced in dogs and cats with various gastrointestinal, pancreatic and hepatic disorders. Anemia or macrocytosis (in cats) may occur but are not common. Bone marrow is typically not evaluated in these disorders.

Answer 264

Cobalamin deficiency resulting from a genetic disorder of intestinal malabsorption has been reported in Giant Schnauzers, Border Collies, Beagles, Australian Shepherd Dogs, and presumptively in one cat. Intrinsic factor deficiency has not been identified in these cases. Signs and severity vary, but generally are associated with failure to thrive. Megaloblastic and other dysplastic changes are present in the bone marrow resulting in normocytic normochromic anemia, increased RDW, and megaloblasts in the peripheral blood. Intramedullary erythrophagocytosis has also been seen, consistent with destruction of dysplastic erythroid cells. Dogs treated with parenteral cobalamin have had correction of anemia and have thrived; the one cat was not treated. Chronic treatment with azathioprine in dogs and methotrexate in cats in the author's practice has been associated with macrocytosis in some cases. Poodles have an inherited disorder of megaloblastic dyshematopoiesis and macrocytosis but are not anemic

Answer 265

Idiopathic bone marrow failure and serous atrophy causing pancytopenia was associated with prolonged anorexia in four cats; malnutrition may have been contributory

Answer 266

IMHA is classically characterized by peripheral destruction of red cells and a strong regenerative response. However, less commonly, an immunologic attack on erythropoiesis occurs “deeper” in the bone marrow instead of, or in addition to, the peripheral blood. This attack may occur at several levels and act as a “dam” in the bone marrow preventing normal maturation and resultant lack of a regenerative response. While in dogs regenerative IMHA is more common than nonregenerative IMHA, this is not the case in cats.

Answer 267

At the first level, an attack on reticulocytes in the blood results in lack of reticulocytes on a hemogram but evidence of synchronous erythroid hyperplasia on bone marrow biopsy. At the next level, an attack on erythroid cells causes a maturation arrest. In some cases the expansion of immature erythroid cells behind the immunologic dam is so prominent that it may be mistaken for erythroid leukemia, similar to the previously discussed situation with early myeloid hyperplasia. In other cases of ineffective erythropoiesis, erythroid production tapers into the later stages on bone marrow biopsy. In both scenarios erythroid dysplasia may be pronounced. If the immunologic attack occurs at the level of the earliest committed erythroid progenitor cells, then a bone marrow biopsy reveals attenuation or absence of all stages of erythropoiesis, and the diagnosis is erythroid hypoplasia or aplasia. If the immunologic attack occurs at the level of pluripotent hematopoietic progenitor cells, then a hemogram reveals pancytopenia and a bone marrow biopsy reveals trilineage hypoplasia or aplasia, often with replacement with adipocytes, and the diagnosis is “aplastic anemia.”

Answer 268

Historically, the term aplastic anemia has been used to denote trilineage bone marrow aplasia, while pure red cell aplasia has been used to identify the condition where only erythroid production is impaired. These are linguistically bad terms, but are conventional. Further permutations on this theme are possible. For example, cases of erythroid and megakaryocytic hypoplasia with normal neutrophil and monocyte production have been seen,because platelets and red cells differentiate from each other after their common progenitor cells differentiate from the neutrophil-macrophage progenitor cells.

Answer 269

In most cases of immunologic attack in the bone marrow the anemia is normocytic normochromic. Serum iron and transferrin levels may be elevated. There is no pathognomonic finding on bone marrow biopsy. Bone marrow plasma cell hyperplasia or lymphocytosis support the diagnosis, but its absence does not rule it out, and caution must be exercised in diagnosing mild plasma cell hyperplasia against a background of reduced bone marrow cell density.

Answer 270

Immune-mediated erythroid hypoplasia and related disorders are presumptively diagnosed on the basis of ruling-out other causes of erythroid hypoplasia, supportive bone marrow biopsy findings, and on response to immunosuppression. Because immunosuppression is not always successful with immune-mediated diseases, lack of response does not rule-out the diagnosis. The diagnosis is also supported by concurrent typically immune-mediated disorders (e.g., polyarthritis), positive antinuclear antibody titer, positive Coombs’ test, and spherocytes and, if thrombocytopenia is present, positive tests for antiplatelet and antimegakaryocyte antibody.

Answer 271

Feline immune-mediated dyserythropoiesis most commonly occurs in young cats and is more likely to explain a FeLV-negative nonregenerative anemia than is a false-negative FeLV test. In addition, while the anemia in some cats has responded to prednisone therapy alone, many cases appear to require more intense immunosuppression. The author prefers to initiate treatment with prednisone, cyclophosphamide, or chlorambucil, and cyclosporine at standard doses. Because the role of hemotropic mycoplasma and ehrlichial infections in the pathogenesis of the disorder is not known, treatment with doxycycline or marbofloxacin is recommended. Testing by polymerase chain reaction (PCR) at a laboratory with a proven track record in quality control may be considered. Over 70% of cats are expected to recover.

Answer 272

IMHA: The signalment of dogs with immune-mediated dyserythropoiesis is typical of IMHA and other immune-mediated disorders, with middle-aged spayed female dogs at increased risk. The tendency is to also treat dogs with a combination of immunosuppressive agents, although the benefit of doing so is not known. Over 70% of dogs are expected to recover, but the response may take weeks. The prognosis may be better in dogs with subacute-to-chronic disease than with typical peracute to acute IMHA because dogs without acute peripheral hemolysis and its associated systemic inflammatory response are at less risk for pulmonary thromboembolism and disseminated intravascular coagulation.

Answer 273

Serum EPO levels are anticipated to be elevated in immune-mediated nonregenerative anemia, therefore EPO therapy is usually not recommended. However, rhEPO therapy has been beneficial in cases of immune-mediated aplastic anemia in humans despite elevated serum EPO levels. Nonetheless, routine treatment with rhEPO is not recommended in dogs and cats where treatment may trigger another antierythroid immune response.

Answer 274

FeLV is not cytopathic but infection of erythroid cells alters or arrests their development, causing a normocytic normochromic anemia. In some cases this may be by mechanisms similar to anemia of inflammatory disease. Macrocytic anemia may occur with some subgroup A strains. Subgroup C causes pure red cell aplasia and may also be responsible for aplastic anemia. Cats infected with FeLV may also develop anemia secondary to hemotropic mycoplasma infections, hematopoietic and nonhematopoietic neoplasia, and possibly IMHA. Endogenous EPO levels are elevated and in principle rhEPO therapy should not help, but there are anecdotal reports of benefit.

Answer 275

Myeloid leukemia refers to neoplasia arising from hematopoietic cells in the bone marrow, be they of erythropoietic, thrombopoietic, granulopoietic, monocytopoietic, mixed-lineage, or pluripotent stem cell origin, with or without overt peripheral blood involvement. The term myeloid in the context of leukemia is thus used to distinguish these leukemias from lymphoid leukemias, while in the context of normal hematopoiesis myeloid refers to granulocyte-monocyte lineage cells as distinct from erythroid cells.

Answer 276

Hematopoiesis is diverted into production of malignant cells, with a resulting decrease in normal blood cell production. The malignant clone arises from a mutant stem cell with pluripotent properties, but it is not known if the mutation occurs in normal hematopoietic stem cells or in more differentiated cells that then acquire stem cell properties.

Answer 277

Any AML may cause anemia, but the most profound tend to be seen with leukemias arising from erythropoiesis, namely erythroleukemia and erythremic myelosis. Generally erythroleukemia is a broader term referring to leukemia arising from a common erythrocyte and leukocyte precursor, while erythremic myelosis refers to leukemia strictly of erythropoietic origin.

Answer 278

In AML arising from mixed-lineage or pluripotent cells, an animal is more likely to be presented for clinical signs due to neutropenia and thrombocytopenia, analogous to the situation with bone marrow destruction. In contrast, in erythremic myelosis, leukocyte and platelet production is more spared, and an animal is more likely to be presented for signs due to anemia. These rules are not absolute, in part because normal blood cell production is also affected by displacement and depression, and the malignant clone may change in character.

Answer 279

Animals with AML are usually presented for inappetence and lethargy. The main physical examination finding in an animal with erythroid leukemia is pallor. Petechiation and ecchymoses may be present if there is thrombocytopenia, but they are more difficult to see compared to an animal with immune-mediated thrombocytopenia because of the anemia. Fever may be present, especially if the animal is neutropenic. Hepatomegaly and/or splenomegaly may occur from leukemic cell infiltration. Lymph node infiltration may also occur, but lymphadenopathy is not typically as marked as with lymphoma.

Answer 280

A hemogram may reveal many combinations of leukemic cells and cytopenias. Abnormal erythroid cells may resemble any prereticulocyte stage of erythropoiesis. Marked nonregenerative anemia is typical, and it is important not to misdiagnose the presence of rubricytes and metarubricytes as a sign of regeneration. Bone marrow biopsy is needed for diagnosis if only anemia with or without other cytopenias is present. If leukemic cells are present in the blood, bone marrow biopsy is not strictly necessary but helps to further characterize the disorder. Bone marrow biopsy of an animal with erythremic myelosis will reveal marked erythroid hyperplasia with maturation arrest and erythrodysplasia

Answer 281

It is difficult to distinguish malignant from nonmalignant causes of erythroid hyperplasia with dyserythropoiesis on the basis of morphology alone. Indeed, in some models of erythroid leukemia the defect is an oncogene-based maturation arrest.

Answer 282

1. First, in cats, a positive ELISA test for FeLV supports the diagnosis, as FeLV is a proven cause of AML. In dogs there is no equivalent cause to FeLV, accounting for the rarity of the diagnosis. The only risk factor for erythroleukemia in the dog is chronic irradiation. 2. The greater the percentage of blasts the greater the likelihood of AML (but >30% is not necessarily a limit) 3. Nonmalignant dyshematopoiesis may yield dysplastic cells in the peripheral blood, but the greater the presence of abnormal cells, the greater the likelihood of leukemia. 4. If hepatomegaly, splenomegaly, or lymphadenomegaly are present, biopsy of these organs may reveal neoplastic cell infiltration. Organomegaly on its own is not sufficient evidence, as this may also occur due to lymphoid hyperplasia in immune-mediated blood disorders. Furthermore, in the latter case biopsy may also reveal extramedullary hematopoiesis, which may mimic neoplasia. 5. The presence of disorders and positive test results characteristic of immune-mediated disorders supports immune-mediated dysmyelopoiesis, although these may have an underlying neoplasm. Finally, AML appears to be uncommon in dogs and FeLV-negative AML is uncommon in cats. Because of the difficulty in confirming a diagnosis of erythroid leukemia, especially in the absence of peripheral blast cells, and the tendency to euthanize animals with AML, if there is ever a place for the clinician to stand by the old adages of “treat for the treatable” and “never let an animal die without the benefit of prednisone,” it is here. Erythroid leukemia is treated with cytotoxic chemotherapy. Fortunately these protocols are also immunosuppressive. than conventional doses.

Answer 283

MDS is characterized by peripheral blood cytopenias, but normal to increased marrow cellularity with dysplastic changes, and a risk of progression to AML. As the name implies, it is a syndrome, not a single disease, and as with AML, classification and nomenclature are evolving. The unifying concept is an abnormal clone of hematopoietic progenitor cells that may suppress, displace, and progressively replace normal hematopoietic tissue. The hematologic and clinical progression is highly variable. It is one more of the many hematologic disorders associated with FeLV infection in cats

Answer 284

Similar to AML, primary MDS appears to be uncommon in dogs, and a positive FeLV ELISA supports the diagnosis of MDS in cats. As with nonregenerative IMHA, positive ANA and Coombs’ tests support immune-mediated myelodysplasia. Detection of more than 5% monoblasts identified by cytochemistry is another criterion proposed as strongly supportive of MDS in dogs. Myelodysplastic changes may also be normal in elderly humans

Answer 285

Displacement of Erythroid Tissue (Myelophthisis) Erythroid cells may be crowded out by metastatic cancer cells, nonmyeloid hematopoietic neoplasia (acute lymphoid leukemia, multiple myeloma, mast cell neoplasia), granulomatous inflammation (e.g., histoplasmosis), or myelofibrosis. In addition to physical displacement, neoplastic cells may depress erythropoiesis by molecular mechanisms. As with other causes of generalized bone marrow injury, neutropenia and thrombocytopenia may be more responsible for clinical signs than anemia. Bone marrow biopsy is diagnostic, and usually nonmyeloid hematopoietic neoplasms do not pose the same diagnostic dilemmas as do AML and MDS.

Answer 286

Another mechanism of displacing hematopoietic cells is myelofibrosis. Myelofibrosis is a nonspecific finding: it may be idiopathic, the result of FeLV infection in cats, chronic inflammation in the bone marrow (including autoimmunity—it is a common finding in immune-mediated erythroid hypoplasia), secondary to a primary leukemia, or in some cases a primary tumor of bone marrow stromal cells. Although neutropenia or neutrophilia, and thrombocytopenia and thrombocytosis, may occur, leukocyte and platelet numbers are often normal, and moderate to severe nonregenerative anemia is the salient finding. The anemia is typically normocytic normochromic, but macrocytosis in one case series of dogs was observed and was associated with a better prognosis. Idiopathic myelofibrosis is usually treated with standard immunosuppressive agents.

Answer 287

Osteopetrosis is a rare condition of young dogs that may cause nonregenerative anemia or pancytopenia secondary to thickening of the cortices and narrowing of the medullary cavity. Osteopetrosis may be a feature of FeLV subgroup C–induced bone marrow failure.

Answer 288

Nonhematologic diseases depress the erythron at various levels and by various mechanisms. Diseases include infectious diseases, nonseptic inflammation, neoplasia, chronic liver diseases, chronic renal failure, and some endocrinopathies. Congestive heart failure is a common cause of anemia and pseudoanemia in humans, but does not appear to be in dogs and cats, although one small study identified lower Hct in dogs with severe heart failure. Some mechanisms of anemia are shared by some of the disorders, but there are enough differences in mechanisms and in onset of anemia that render “anemia of chronic disease” too broad a term. It has been hypothesized that reduced activity associated with chronic illness results in fatty replacement of hematopoietic tissue and that this is a common mechanism that has been overlooked

Answer 289

Anemia of Inflammatory Disease (AID) and Cancer-Associated Anemia Anemia of inflammatory disease (AID) is caused by complex cytokine derangements that decrease EPO production, EPO function, iron metabolism, and red cell lifespan.[203-205] A key event is the sequestration of iron, which is considered to be an adaptive mechanism that renders the micronutrient unavailable to infecting microorganisms.[206,207] These mechanisms are present in acute inflammation, and Hb levels begin to decrease in several days, but actual anemia develops only in more chronic inflammation because of red cell lifespan.

Answer 290

The anemia is usually mild to moderate, but may be severe, especially in cats, in part because of the shorter red cell lifespan. The anemia is initially normocytic and normochromic, but may progress to microcytic and hypochromic in dogs. Serum iron should be low-normal to low, but in contrast to iron deficiency, AID is supported by documenting low-normal to decreased transferrin, and high-normal to elevated ferritin. Bone marrow biopsy should reveal normal to mildly depressed erythropoiesis with normal to increased iron in dogs. The mechanisms responsible for AID are considered responsible for cancer-related anemia not attributable to other causes, and the anemia is initially mild, normocytic, and normochromic. Iron sequestration has been shown in dogs with lymphoma and osteosarcoma.

Answer 291

Anemia at diagnosis and during therapy may be negative prognostic factors for various tumors in humans, and definitely have a negative impact on quality of life.[211-216] Tumor hypoxia is a well-recognized mechanism of resistance, and it is possible that anemia favors resistance to treatment and tumor progression.[217] Conversely, increasing iron load with transfusion or rhEPO treatment is potentially detrimental. Analogous to iron sequestration in AID being a protective mechanism against microbial proliferation, iron sequestration in paraneoplastic AID may be protective. Neoplastic cells have a higher iron requirement due to rapid proliferation, and iron chelators have anticancer properties.[218] An additional concern is that treatment with EPO may stimulate tumor progression, perhaps because some tumors express EPO receptors.[219] However, EPO may also have an anticancer effect in some tumors such as multiple myeloma.[220] Treatment with EPO increases the risk of venous thrombosis.[216] Correcting anemia improves quality of life, but the effect on tumor response, tumor progression, and overall patient survival is not clear.[216] The current recommendation in veterinary medicine is to treat anemia in the oncology patient using the same transfusion triggers as with patients with nonneoplastic disorders. Some patients with advanced cancer and chronic anemia have been transfused in the author's practice at a higher trigger than with chronic anemia due to other causes, in an effort to improve quality of life. Response has been variable, consistent with the observation in humans that factors other than anemia contribute to fatigue.[221] Treatment with rhEPO has also anecdotally been used for this purpose in dogs and cats. It is not known if the risk for antibody formation is the same in this group of patients as in patients with chronic renal failure.

Answer 292

Tumor hypoxia is a well-recognized mechanism of resistance, and it is possible that anemia favors resistance to treatment and tumor progression. Conversely, increasing iron load with transfusion or rhEPO treatment is potentially detrimental. Analogous to iron sequestration in AID being a protective mechanism against microbial proliferation, iron sequestration in paraneoplastic AID may be protective. Neoplastic cells have a higher iron requirement due to rapid proliferation, and iron chelators have anticancer properties. An additional concern is that treatment with EPO may stimulate tumor progression, perhaps because some tumors express EPO receptors. However, EPO may also have an anticancer effect in some tumors such as multiple myeloma. Treatment with EPO increases the risk of venous thrombosis.

Answer 293

Anemia was present in 36% of FIV-positive cats in one case series. Some of the anemias seen with FIV are due to secondary diseases, including hemotropic mycoplasma infections and neoplasia, but anemia may occur without these. The virus is not cytopathic and does not infect erythroid cells. Recent studies have shown that, similar to HIV, FIV does infect ................. and bone marrow ..............cells, and the latter is likely involved with in depressing erythropoiesis through alterations in the marrow inductive microenvironment. Another mechanism may be infection of ......... cells involved in regulating hematopoiesis. Bone marrow findings include erythroid hyperplasia with megaloblastic dysplasia and ineffective erythropoiesis.

Answer 294

AID, Malnutrition, Reduced red cell lifespan, Hemorrhage due to gastrointestinal ulceration, Coagulopathy, Hepatic rupture. Excluding major hemorrhage, the anemia is usually mild to moderate normocytic normochromic and is not responsible for presentation to the clinic. Poikilocytosis is common, including target cells in dogs, probably due to abnormal lipids in the red cell membrane.

Answer 295

Due to EPO deficiency, Decreased red cell lifespan, Uremic bleeding. The benefits of EPO supplementation go beyond the correction of anemia and hopefully routine supplementation will become easier in the future.

Answer 296

Anemia in hypothyroidism is considered an adaptation to decreased oxygen demands due to decreased basal metabolic rate, and thus is a consequence, rather than cause, of lethargy. Thyroid hormone normally stimulates burst-forming units–erythroid and colony-forming units–erythroid directly and indirectly via EPO, and it also stimulates 2,3-DPG synthesis. The prevalence and severity of decreased red cell mass may be underestimated by these figures, as plasma volume is also decreased in hypothyroidism. Anemia is typically normocytic normochromic with normal red cell survival.

Answer 297

Dogs with both typical and glucocorticoid only–deficient hypoadrenocorticism often have low-normal to low Hct. Glucocorticoids enhance erythropoiesis and this is part of a normal stress response. The mechanisms are not completely known, but they include stimulation of glucocorticoid receptors on erythroid progenitor cells. Anemia is normocytic normochromic and is usually mild to moderate. With chronic hypoadrenocorticism the anemia may be severe. Acute gastrointestinal hemorrhage from ulceration may also contribute to anemia, and may also be a mechanism for hypoalbuminemia. Anemia may be masked on presentation by dehydration. Hypoadrenocorticism is less common in cats than dogs, and anemia is both less common and less severe

Answer 298

Anemia is common in critically ill patients because of repetitive blood sampling, surgery, gastrointestinal ulceration, AID, decreased red cell lifespan, and nutritional deficiencies. Transfusion triggers are controversial. The current recommendation in dogs and cats is to transfuse based on the same criteria as in anemia due to other causes.

Answer 299

Dilution (Pseudoanemia) Fluid therapy with either crystalloids or colloids will decrease Hct. This is not usually a concern in anemic animals as red cell mass is not affected. Indeed, in anemic dehydrated animals there is likely to be improved tissue oxygenation because of improved circulation.

Answer 300

Pregnancy Plasma volume expansion occurs during pregnancy, probably due to systemic vasodilation and the resulting increase in vascular capacitance. Erythropoiesis also increases during pregnancy, but the degree of plasma volume expansion is relatively greater than the increase in red cell mass; therefore, Hct decreases. (Albumin levels also decrease, although altered albumin metabolism is also involved.) The volume expansion and erythroid hyperplasia are believed to be adaptive mechanisms to improve placental circulation, in part by lowering blood viscosity. Other benefits include a mechanism to counter the increased risk of thrombosis due to thrombocytosis and elevated fibrinogen, and a volume reserve to buffer hemorrhage during parturition. In dogs, the Hct slowly declines during gestation. In a study of six cats, mean Hct 1 day after breeding was 36% and dropped to 28% at term. A mild increase in aggregate and punctuate reticulocytes was reported.

Answer 301

In dogs: Estrogens; Phenylbutazone, Meclofenamic acid, Carprofen; Captopril, Quinidine; Thiacetarsemide, Albendazole, metronidazole, Phenobarbital. Phenytoin may cause macrocytosis. In cats: Griseofulvin may cause bone marrow failure (especially in FIV-positive cats), Antithyroid drugs may cause anemia and other cytopenias. Cephalosporins and trimethoprim-sulfonamides at normal doses have been rarely associated with adverse hematologic reactions in both species. Recombinant human EPO may result in immune-mediated pure red cell aplasia in both species with a risk of 20% to 25%.

Answer 302

Trimethoprim-sulfonamides at high doses has caused mild anemia from folate inhibition in normal dogs and delayed recovery in dogs during bone marrow transplantation. Chloramphenicol causes reversible erythroid suppression by inhibiting Hb synthesis in all species.

Answer 303

Acoagulopathy is any defect in the body's ability to clot. Defects in blood clotting can lead to either a state of hypocoagulability or hypercoagulability.

Answer 304

Vitamin K deficiency is one the most commonly acquired coagulopathies in small animals. Deficiency most commonly results from ingestion of vitamin K antagonist rodenticides; however, decreased synthesis from the intestinal microflora along with decreased vitamin K absorption have also been reported.

Answer 305

Vitamin K1 (phylloquinone), which is derived from green leafy plants and is absorbed through the lymphatics in the proximal small intestine. Vitamin K2 (menaquinone); which is synthesized by bacterial microflora (E. coli and Bacteroides predominantly) in the ileum and colon. Synthetic vitamin K3 (menadione), which is a synthetic form that must be metabolized to vitamin K2 to be activated.

Answer 306

Mammals have developed an efficient system for recycling vitamin K which explains why minute amounts are sufficient to cover the daily requirements. In health, daily vitamin K requirements for the dog have been estimated at 1.25 µg/kg/day and the liver contains several days supply.

Answer 307

Vitamin K plays an important role as a cofactor in the intrinsic, extrinsic and common pathways where it is essential in the activation of the vitamin K–dependent clotting factors II, VII, IX, and X and proteins C and S. Factors II, VII, IX, and X are produced in the liver as inactive precursors. These precursors contain gamma glutamyl amino acid groups that, in the presence of vitamin K, will undergo carboxylation, allowing calcium binding and thus clotting. The carboxylation reaction requires reduced vitamin K. However, during carboxylation, vitamin K becomes oxidized by the enzyme vitamin K epoxidase and becomes vitamin K epoxide. To allow continued factor activation, this vitamin K epoxide must be once again reduced by vitamin K epoxide reductase.

Answer 308

Some anticoagulant rodenticides currently on the market inhibit this process leading to the release of dysfunctional forms of the clotting factors II, VII, IX, and X into circulation (Figure 192-1). Recently, the key protein, vitamin K epoxide reductase complex subunit 1 has been identified as the key protein of the vitamin K cycle and is an area of intense research. Inhibition of vitamin K epoxide reductase leads to rapid depletion of the vitamin K–dependent clotting factors. Because factors II, VII, IX, and X have very short half-lives in the dog, a coagulopathy quickly develops.

Answer 309

Figure 192-1 Vitamin K epoxidase cycle illustrating the carboxylation of clotting factors and the site of warfarin inhibition. 

Answer 310

Ingestion of coumarin-based rodenticides is the most common cause of vitamin K–deficient coagulopathy in small animals. Warfarin was the first of the anticoagulant rodenticides developed; however, rats quickly developed resistance to warfarin leading to the development of the more potent second generation products with longer half-lives (bromadiolone, brodifacoum, and diphacinone). Once ingested, warfarin is transported to the liver and excreted through either urine or bile, where it may undergo enterohepatic recirculation

Answer 311

Dogs and cats consuming rodents intoxicated with anticoagulant rodenticides are unlikely to be affected. The amount of rodenticide ingested by the rodent or the residue concentration is believed to be so small that a large number of intoxicated rodents would have to be ingested to result in toxicosis.

Answer 312

Clinical signs associated with anticoagulant rodenticide toxicity develop 2 to 5 days following exposure. Based on a retrospective of 21 dogs, the most common presenting complaints and physical examination findings were dyspnea (57%), lethargy (48%), coughing/hemoptysis (30%), pallor (26%), epistaxis (17%), vomiting (17%), melena (17%), hematochezia (13%), lameness (13%), spontaneous subcutaneous hematoma (13%), ecchymoses (13%), hematoma at intramuscular injection sites (9%), hematuria (9%), gingival bleeding (9%), and collapse (9%).[4]

Answer 313

Following ingestion, the first test to show an abnormal result is the proteins induced by vitamin K absence (PIVKA) within 12 hours, followed by the prothrombin time (PT) within 36 to 72 hours, then the partial thromboplastin time (PTT). Animals presenting with clinical signs typically have a prolonged activated clotting time (ACT), PT, and PTT. Anemia (83%), thrombocytopenia (61%), hypoproteinemia (57%), and increased fibrin degradation products (FDP) (55%) were also reported in the previous study (Table 192-1).

Answer 314

PIVKA has been shown to have high sensitivity and specificity for rodenticide anticoagulants. Measurement of rodenticide concentrations in serum, blood or tissue is necessary to confirm exposure, especially in cases having legal implications.

Answer 315

PT should be measured 48 hours after discontinuation of therapy. Therapy in a bleeding patient consists of restoring functional clotting factors. This can be done through plasma or blood transfusion and the administration of vitamin K1. As it may take up to 12 hours before functional clotting factors are present in circulation following initiation of vitamin K therapy, a transfusion may be necessary. Length of administration is based on the half-life of the ingested rodenticide. A 2- to 4-week therapy has been recommended for second generation rodenticides. A PT should be measured 48 hours following discontinuation of therapy, and if it is prolonged, therapy should be resumed for 2 more weeks.

Answer 316

Vitamin K1 should never be given intravenously as it has been associated with anaphylaxis. Vitamin K3 should not be used as it has a delayed onset of activity and has been reported to cause Heinz body anemia.

Answer 317

Although less common, vitamin K deficiency can also develop secondary to decreased synthesis by the intestinal microflora. This can result from chronic antibiotic therapy. Severe fat malabsorption such that can occur secondary to complete bile duct obstruction, exocrine pancreatic insufficiency, and lymphangiectasia can result in vitamin K deficiency. Therapy should be aimed at correcting the underlying disorder and parenteral vitamin K1 administration

Answer 318

LIVER DISEASE The liver plays a central role in coagulation homeostasis. Hemostatic abnormalities are common in liver disease and have been estimated to occur in 70% to 85% of human patients; however, clinical bleeding is much less common (

Answer 319

Liver disease is typically associated with coagulopathies when liver reserve is poor. Liver failure results in multiple changes in the hemostatic system because of reduced synthesis of procoagulant and anticoagulant factors. Factor deficiency is attributed to decreased factor synthesis, abnormal factor synthesis, and excessive consumption.

Answer 320

Clotting factor deficiencies have been correlated to the degree of hepatocellular necrosis and the concurrent decrease in albumin. In some instances, prolonged bleeding times may be documented before the decrease in albumin given the shorter half-lives of the clotting factors. Added to all these other anomalies is vitamin K deficiency which was previously discussed. During failure, the liver is unable to clear activated hemostatic proteins and inhibitor complexes from the circulation. Given these various anomalies, the global effect of liver failure on hemostasis is complex and may result in bleeding or thrombosis.

Answer 321

Portal hypertension often accompanies liver disease and may result in splenomegaly and thrombocytopenia through platelet sequestration.

Answer 322

Sluggish blood flow through the portal vein secondary to hypertension can also lead to portal vein thrombosis.

Answer 323

Decreased thrombopoietin production and decreased platelet function have also been reported in liver failure.

Answer 324

Thrombocytopenia, impaired platelet function and vessel wall interaction, decreased levels of clotting factors II, V, VII, IX, X, XI, dysfibrinogenemia, and decreased alpha2-antiplasmin.

Answer 325

Elevated levels of factor VIII and von Willebrand factor, Decreased proteins C and S and antithrombin, and Decreased levels of plasminogen. Thromboelastography in people with cholestatic liver disease show either a normo- or hypercoagulable tracing

Answer 326

Patients with neoplasia may present with bleeding or thrombosis from various causes. Hemostatic abnormalities reported in cancer patients can be caused by thrombocytopenia, thrombocytopathia, DIC, release of factors from tumor cells, tumor-induced organ dysfunction, microangiopathy, endothelial invasion by neoplastic cells, and the administration of various chemotherapeutic agents.

Answer 327

The pathogenesis of DIC in cancer patients is multifactorial and results from systemic generation of thrombin and plasmin leading to fibrin polymerization and subsequent fibrinolysis. As this cycle continues, it results in depletion of clotting factors, platelets and fibrinogen. The most common manifestations in a canine study were thrombocytopenia and prolonged PTT. Tumors most commonly associated with DIC were hemangiosarcoma, inflammatory mammary tumors, thyroid carcinoma, primary lung tumors, and intraabdominal carcinomas. Other tumors associated with hemostatic abnormalities in small animals are multiple myeloma, mast cell tumors and lymphoma

Answer 328

DIC, also known as consumptive coagulopathy, is a syndrome that can complicate many disease processes and lead to life-threatening hemorrhage. It is considered a secondary disease because an original insult predisposing to thrombosis must be present to initiate DIC. It can be defined as a pathologic activation of clotting factors leading to formation of disseminated microthrombi. Microthrombi consume clotting factors along with platelets, resulting in their depletion. Severe clotting factor depletion then leads to hemorrhage from venipuncture sites or digestive, respiratory, urinary, or reproductive tracts.

Answer 329

Microthrombi result in poor tissue and organ perfusion, which may lead to multiple organ dysfunctions. Regardless of the underlying disease, once initiated, the pathophysiology of DIC is similar.

Answer 330

A critical mediator of DIC is the release of tissue factor, a transmembrane protein present on the surface of most cells. In health, tissue factor does not come into contact with the general circulation. However, in inflammation, tissue factor can be expressed on endothelial cells within the circulation and on some neoplastic cells. Tissue factor can also be released into circulation in response to proinflammatory cytokines (interleukin-1, tumor necrosis factor) and endotoxin. Once in circulation, tissue factor forms a complex with factor VIIa, a potent stimulus for thrombin formation. Excess circulating thrombin cleaves fibrinogen leaving behind multiple fibrin clots leading to microvascular and macrovascular thrombosis. Thrombin and fibrin production become exaggerated.

Answer 331

DIC is a mixed coagulopathy as throughout its course, the patient may undergo phases or hypo- or hypercoagulability. Coagulation inhibitors are also consumed in this process. Decreased inhibitor levels lead to more clotting so that a feedback system occurs in which increased clotting leads to more clotting. Concurrently, thrombocytopenia due to entrapment in clots and excessive consumption also occur. Clotting factors are consumed in the development of multiple clots, which contributes to the bleeding seen with DIC

Answer 332

Simultaneously, excess circulating thrombin results in the conversion of plasminogen to plasmin, leading to fibrinolysis. Fibrinolysis results in excess amounts of FDPs, which have anticoagulant properties, possibly contributing to hemorrhage. Excess plasmin also activates the complement and kinin systems, leading to clinical signs such as shock, hypotension, and increased vascular permeability. The hypercoagulable state occurs early in the course of DIC and prolonged clotting times accompanied by bleeding usually occur later in its course.

Answer 333

Diagnosis of DIC is based on clinical findings and laboratory testing; however, given its dynamic nature and considerable variation in coagulation profiles of affected dogs, establishing a diagnosis can be challenging. Any animal having experienced prolonged hypotension, systemic inflammatory response syndrome, disturbed blood flow to a major organ, or major tissue trauma is at high risk of developing DIC. Patients in acute fulminant DIC present with bleeding; however, in more chronic forms patients may only show signs related to the underlying disorder

Answer 334

Prolongation of coagulation times, thrombocytopenia, elevation of d-dimer or soluble fibrin, decrease in antithrombin, Clinical or postmortem evidence of thrombosis. A recent study reported that thromboelastography was valuable in the assessment of 50 dogs presenting in DIC. The majority of these patients were found to have hypercoagulable tracings. In this study, mortality was associated with high D-dimer, low antithrombin, and hypocoagulable thromboelastographic tracings as compared to survivors. A canine study indicated that a negative D-dimer test excludes DIC as a diagnosis with a confidence interval of 95%.

Answer 335

Therapy is multifaceted and should be aimed at ensuring adequate tissue perfusion, eliminating the initiating cause, supporting target organs, replacing blood components, and initiating anticoagulant therapy. Blood component replacement can be provided by plasma transfusions, which can help replace clotting factors in order to rebalance coagulant and anticoagulant proteins. Fresh whole blood, platelet-rich plasma, or concentrates may be indicated in some patients. Antithrombin replacement has been attempted in people with no improvement in mortality seen. Activated protein C may reduce organ damage in human patients with sepsis and DIC but this has yet to be investigated in veterinary medicine.

Answer 336

Heparin is a glycosaminoglycan that exerts its effects by binding to antithrombin and accelerating its interaction with activated factors IIa (thrombin), IXa, Xa, XIa, and XIIa. Thrombin and factor Xa are most responsive to inhibition by antithrombin. Thrombin inactivation requires formation of a ternary complex involving heparin, AT, and thrombin. Heparin is an indirect anticoagulant, exerting most of its effect through potentiation of AT activity. The drug is administered either intravenously or subcutaneously, as it is very poorly absorbed orally. Heparin has long been the mainstay of DIC therapy despite few reports documenting its true benefit. Increased morbidity has been reported in people in DIC who receive heparin while actively bleeding. Heparin does not eliminate existing thrombi but may prevent the formation of new thrombi. Overall prognosis for DIC is poor and varies depending on the underlying disorder. DIC has also been referred to as “death is coming.”

Answer 337

Normal hemostasis is maintained through an intricate balance between endogenous anticoagulants and procoagulants. Changes in this balance can tip the scales to either excessive bleeding or widespread thrombus formation (hypercoagulability). The concept of “Virchow's Triad” (endothelial damage, alterations in blood flow, and hypercoagulability) refers to underlying factors that act singly or together to promote thrombus formation in various disease states. The primary disorder influences the site of thrombus formation (arterial or venous vasculature), the composition of the occluding thrombus, and the approach to antithrombotic therapy.

Answer 338

The relative proportions of platelets and fibrin in the clot depend on the shear of the injured vessel. Arterial thrombi form under high shear forces and therefore tend to contain a large number of platelets held together by fibrin strands. Venous thrombi form under low shear forces and consist primarily of fibrin and red blood cells. Mixed thrombi are an intermediate form and occur in the pulmonary vasculature.

Answer 339

Strategies to inhibit arterial thrombogenesis typically include the use of antiplatelet drugs, whereas anticoagulants are the mainstay of venous thromboprophylaxis. Ultimately, clinical trials are required for optimization of drug dosages and drug combinations for specific thrombotic syndromes

Answer 340

Clinical signs of a thrombus can be variable and depend on the affected organ. Clinical signs result from compromised blood flow to the organ. Thrombi may obstruct flow locally or break off and lodge downstream, where the vessel caliber is smaller and there is slower flow. Acute pulmonary thromboembolism is associated with dyspnea. Renal arterial thromboembolism can be associated with acute renal failure.

Answer 341

Diagnosis of hypercoagulability is a great challenge in veterinary medicine. Routine coagulation tests (PT, PTT) are designed to detect “hypocoagulability” and assays that measure consumption of anticoagulant proteins and fibrinogen are generally insensitive indicators of subclinical thrombosis. Nevertheless, low plasma AT activity and high FDP, D-dimer, and fibrinogen levels provide laboratory evidence of hypercoagulability.

Answer 342

In human studies, platelet hyperaggregability and expression of platelet activation markers such as P-selectin have been observed in patients with thrombotic tendencies. Thromboelastography (TEG) is a technique that depicts global hemostasis, beginning with clot formation and ending with clot lysis. Characteristic changes in the TEG profile have been associated with hypercoagulability in people. Evaluation of platelet function and TEG may prove useful in future veterinary studies to detect hypercoagulability and to monitor antiplatelet and anticoagulant therapy.

Answer 343

Treatment of thrombosis can be aimed at reducing thrombogenesis or dissolution of existing clots through the use of thrombolytic agents. Reducing thrombogenesis can be achieved with antiplatelet drugs or anticoagulants. Antiplatelet agents act through inhibition of platelet activation pathways or interference with membrane receptors. The three classes of antiplatelet drugs in current use include nonsteroidal antiinflammatory drugs (cyclooxygenase inhibitors), thienopyridines (ADP receptor antagonists), and GPIIb/IIIa blockers (fibrinogen receptor antagonists).

Answer 344

Aspirin is the most common antiplatelet drug used in veterinary medicine. It acts through irreversible acetylation of the platelet cyclooxygenase active site leading to decreased thromboxane A2 synthesis. The effects of aspirin are permanent and last for the lifespan of the platelet (7 to 10 days). In a retrospective study of IMHA in dogs, improved survival was attributed, in part, to low-dose (0.5 mg/kg PO) aspirin administration.

Answer 345

Thienopyridines irreversibly inhibit the binding of ADP to specific platelet ADP receptors (P2Y12).

Answer 346

ADP receptor blockade impairs platelet release reaction and ADP-mediated activation of GPIIb/IIIa, thereby reducing primary and secondary aggregation response. These drugs must be metabolized by hepatic cytochrome p450, with platelet inhibition occurring by 3 days after initiation of therapy. Clopidogrel, given to cats at dosages of 18.75 to 75 mg PO q24h was well tolerated and resulted in significant antiplatelet effects

Answer 347

Activation of GPIIb/IIIa is the final common pathway of platelet aggregation regardless of the initiating stimulus. Although dogs have been used in pharmacokinetic and pharmacologic studies of GPIIb/IIIa antagonists, clinical studies have not been performed

Answer 348

Anticoagulants inhibit the generation of fibrin, but do not dissolve preexisting fibrin clots. Anticoagulants are used for thromboprophylaxis in patients considered at risk for a first thrombotic event and to limit fibrin formation in patients with documented thromboembolic disease. There are currently three anticoagulants in clinical use: warfarin, heparin, and low–molecular weight heparins.

Answer 349

Warfarin is a vitamin K antagonist that alters the synthesis of vitamin K–dependent clotting proteins (Factors II, VII, IX, X) and the anticoagulants, proteins C and S. Warfarin interferes with hepatic reductase activity leading to impaired post-translational carboxylation. Warfarin's anticoagulant activity is delayed (4 to 5 days) as the newly synthesized inactive clotting proteins gradually replace their functional counterparts. Warfarin is administered orally at an initial dose of 0.2 mg/kg PO q12h in dogs and 0.1 to 0.2 mg/kg PO q24h in cats. Close monitoring for dosage adjustment is essential because warfarin's anticoagulant effect is highly variable from one patient to another. Therapy is monitored based on PT, with a target prolongation to 1.5 times baseline. Due to the variability in PT reagent sensitivity, the World Health Organization has recommended that the PT be expressed as a ratio (International Normalized Ratio [INR]). The INR formula incorporates a factor (ISI) specific to each thromboplastin reagent, and is calculated as follows: INR = (patient PT/control PT) ISI. An INR target range of 2 to 3 is considered optimal, without causing excessive bleeding, for most human thrombotic syndromes. INR or PT monitoring is recommended daily for the first week of warfarin therapy, twice weekly for 3 weeks, then once a week for 2 months, then every 2 months. Dose adjustments should be based on the total weekly dose. Despite close monitoring, bleeding complications commonly (20%) occur.[17]

Answer 350

Heparin has been the anticoagulant of choice for thromboprophylaxis and treatment of thrombosis in human and veterinary medicine. Despite its widespread use, heparin has a complex pharmacokinetic profile that produces an unpredictable anticoagulant effect. Heparin therapy is monitored by measurement of the PTT, with dosage adjustment to prolong values to 1.5 to 2.5 times the control value.

Answer 351

Low–molecular weight heparins (LMWHs) are produced by depolymerization of heparin. Like heparin, LMWHs bind to AT and accelerate its inhibition of Factor Xa. LMWHs bind poorly to plasma proteins and cells and undergo first order renal clearance. Dalteparin given to dogs at 150 U/kg q8h resulted in anti-Xa activity in the range 0.2 to 1.0 U/mL. In contrast, pharmacokinetic studies of dalteparin and enoxaparin in healthy cats revealed rapid absorption and elimination of the drugs, with peak effects at 2 to 3 hours post drug administration. In contrast, the predicted dosages required to maintain anti-Xa activity at levels equal to or higher than 0.5 U/mL in cats were 150 IU/kg q4h for dalteparin and 1.5 mg/kg q6h for enoxaparin. LMWHs have the advantage of less intense monitoring and can be administered on an outpatient basis, thus facilitating thromboprophylaxis.

Answer 352

Thrombolytic drugs are less commonly used and target the clot directly by accelerating fibrinolysis. These agents can be infused directly into the clotted vessel if given systemically. Tissue plasminogen activator, streptokinase, and urokinase have also been used with variable outcomes in veterinary patients.

Answer 353

ACQUIRED ANTICOAGULANTS Acquired anticoagulants or inhibitors of coagulation have been reported in humans, laboratory animals, and small animals. These circulating anticoagulants are primarily made up of immunoglobulins of the IgG class directed against one or many coagulation factors. These inhibitors have been most commonly reported in patients receiving multiple whole blood or plasma transfusions (factor VIII inhibitor in hemophilia). Interference inhibitors, blocking more than one coagulation factor, have been reported in immune-mediated disease, secondary to drug reactions, lymphoproliferative disease (paraproteins block receptors on platelets), DIC and neoplasia. The lupus anticoagulant, reported in one dog, is an antiphospholipid autoantibody directed against phospholipids and protein complexes associated with cell membranes. Lupus anticoagulant thus interferes with the interaction between the clotting factors and cell membranes.

Answer 354

Clinical signs can be variable and depending on the site of action of the inhibitor can vary from bleeding to thrombosis to no clinical signs but altered coagulation test results. The presence of an inhibitor is suspected when coagulation test results do not fit the clinical image. With acquired bleeding conditions, the mixing of the patient's plasma with normal species specific plasma should correct any prolongation of clotting. In the presence of inhibitors, correction does not take place. Before concluding that an inhibitor is present, it is essential to make sure the patient is not receiving anticoagulant or antiplatelet medications. Treatment options may involve immunosuppression, specific factor transfusions, desmopressin, monoclonal antibodies or administration of recombinant factor VIIIa.

Answer 355

In the dog and cat, peripheral blood leukocytes comprise granulocytes (neutrophils, eosinophils, and basophils), lymphocytes, and monocytes. Mast cells and plasma cells are not usually present in the circulation unless associated with certain inflammatory, immunologic, or neoplastic disorders.

Answer 356

Peripheral blood leukocytes are formed in the bone marrow and occasionally in extramedullary sites, such as spleen and liver. The absolute number of leukocytes in the peripheral blood is relatively constant in health as production and loss maintain a steady state.

Answer 357

Hemopoietic stem cells give rise to common myeloid progenitors and common lymphocyte progenitors in the bone marrow. These multilineage progenitors differentiate, through several steps, to unilineage committed progenitors under the influence of specific growth factors. These include: granulocyte colony-stimulating factor (G-CSF) for neutrophils; interleukin (IL)-5 for eosinophils; stem cell factor (SCF) for basophils; macrophage colony-stimulating factor (M-CSF) for monocytes; IL-7 and IL-2 for T lymphocytes; IL-15 for natural killer lymphocytes; and IL-4 for B lymphocytes.

Answer 358

Granulopoiesis, the production of neutrophils, eosinophils, and basophils, takes about 6 days from hemopoietic stem cell to mature granulocyte in dogs and cats. One half of this time is spent in the proliferating/mitotic pool and the other half in the maturing/storage pool. Studies suggest that the first cells entering the storage pool are the first to enter the peripheral circulation. Transit times can be markedly shortened with increased demand, particularly from infections.Neutrophils live in the peripheral blood for about 12 hours and can survive in tissues for another 12 hours.

Answer 359

Although the longevity of neutrophils in tissues is generally controlled by the rate of programmed cell death (apoptosis), inflammatory processes can have marked effects on survival times in tissues as well as transit times in bone marrow and peripheral blood. Senescent neutrophils are lost from mucosal surfaces, particularly in the gastrointestinal and respiratory tracts, or are phagocytosed by tissue macrophages.

Answer 360

Neutrophils exist in one of two compartments in the peripheral blood—the circulating pool or the marginating pool (Figure 193-2). Both compartments are freely interchangeable and about equal in size.

Answer 361

Cells in the marginating pool travel close to the inner vessel wall and, mainly in small capillaries, roll slowly along the endothelial surface in preparation to migrate into a site of inflammation. Neutrophils in the marginating pool are also available to enter the circulating pool in response to epinephrine release or strenuous exercise. Venipuncture draws from the circulating leukocyte pool; therefore, leukogram findings represent the total number and specific leukocyte types in the circulating pool.

Answer 362

Neutrophils leave the circulation in a random manner, i.e., those that have just arrived from the bone marrow are as likely to exit as those that have been circulating for several hours. Migration of neutrophils into sites of inflammation varies between the rich capillary bed in the lung and postcapillary venules. Physical trapping of neutrophils in small diameter capillaries is an important means of sequestering inflammatory cells, whereas, adhesion molecules are required to draw neutrophils to inflammatory sites in postcapillary venules.

Answer 363

Inflammation normally follows a certain pattern: increased local blood flow; increased vascular permeability; and recruitment of leukocytes. Leukocytes in the marginating pool engage in low-affinity rolling interactions with the endothelium via selectins. However, with local production of inflammatory mediators, expression of complementary adhesion molecules is up-regulated on rolling leukocytes and endothelial cells. Firm adhesion is mediated primarily by integrins, expressed on leukocyte surfaces, binding to their ligands on endothelial cells. Leukocytes then migrate between or through endothelial cells and across basement membranes toward the site of infection or injury. Chemoattractants elaborated at the inflamed site are responsible for the unidirectional migration of leukocytes toward the damaged tissue. Neutrophils are usually first to arrive, followed by macrophages and lymphocytes; however, the pattern may change depending on the nature of the invader.

Answer 364

However, neoplastic processes (e.g., as a paraneoplastic event or primary neoplasia of neutrophils) and functional defects (e.g., canine leukocyte adhesion deficiency) can also result in neutrophilia. In addition to acute, overwhelming inflammation, neutropenia can result from increased peripheral destruction (e.g., immune-mediated neutropenia or destruction by aberrant cell populations, usually neoplastic and non-neoplastic monocyte lineage cells)[9] or from decreased production related to bone marrow pathology (e.g., necrosis; certain viral infections, such as parvovirus and feline leukemia virus; drug reactions, such as phenobarbital[10]; toxicity, such as estrogen administration or abnormal endogenous production; and myelophthisis [replacement of hemopoietic tissue in the bone marrow by abnormal tissue]).

Answer 365

Eosinophil production is influenced greatly by IL-5; as such, diseases characterized by T helper 2 (Th2) lymphocyte-mediated immune responses and excess IL-5 release may result in eosinophilia. However, eosinophilia can occur in the absence of Th2 dominance, suggesting that other eosinophil mediators are responsible for eosinophil stimulation and recruitment with certain conditions. The lower reference limit for absolute canine and feline eosinophil numbers is 0 or near 0; therefore, eosinopenia is not recognized in these species and abnormalities detected on the leukogram are restricted to eosinophilia and morphologic changes.

Answer 366

Given that the eosinophil is primarily a tissue-dwelling cell, considerable accumulation of eosinophils can occur within tissues without an accompanying eosinophilia, particularly if the process is well established and a “steady state” has been reached between bone marrow production of eosinophils and egress into the site. Eosinophilia can be associated with: allergic reactions; parasitic infections; inflammatory processes associated with release of eosinophilotropic factors; neoplasia (eosinophilic leukemia); paraneoplastic process (e.g., secondary to mast cell neoplasia or T lymphocyte neoplasia);hypoadrenocorticism; or idiopathic causes (e.g., idiopathic hypereosinophilic syndrome), which can be difficult to distinguish from eosinophilic neoplasia. Morphologic changes can be seen in circulating eosinophils with increased demand, neoplasia, breed-related finding (e.g., Greyhound dogs), and Pelger-Huët anomaly (discussed later).

Answer 367

Basopenia (or basophilopenia), like eosinopenia, is not appreciated given the lower limit of the reference interval for these cells in peripheral blood. Basophilia may accompany eosinophilia in allergic reactions and parasitic infections. Basophil numbers can also be increased with neoplasia (basophilic leukemia) or as a paraneoplastic event (e.g., mast cell tumor or other myeloproliferative disorder).

Answer 368

Lymphopenia is one of the most common leukogram changes identified in veterinary medicine, probably because most CBCs are performed on sick animals and these animals are likely to be “stressed” and producing increased levels of endogenous corticosteroids. Return of lymphocyte numbers often parallels recovery in these animals, serving as a good prognostic sign. Additional causes of lymphopenia are: hereditary and acquired immunodeficiency diseases; acute viral and bacterial infections (not distinguishable from a stress response); immunosuppressive therapy and chemotherapy; and internal or external loss of lymph.

Answer 369

Lymphocytosis should be interpreted relative to age of the animal, vaccination history, and whether the animal is clinically ill. Lymphocyte numbers that are within reference limits or increased in an ill dog suggest the possibility of a glucocorticoid deficiency. Fractious cats, or cats likely to have high levels of endogenous epinephrine for any reason, may have transient lymphocytosis that relates to circumstances around the time of venipuncture. A follow-up CBC when the cat is more relaxed can aid in differentiating epinephrine-induced lymphocytosis from other causes of lymphocytosis. Additional causes of lymphocytosis include chronic antigenic stimulation, recent vaccination, and neoplasia. Morphologic features sometimes aid in differentiating neoplastic and nonneoplastic lymphocyte disorders; however, there is considerable overlap between features of reactive/immunologically stimulated lymphocytes and neoplastic lymphocytes.

Answer 370

MONOCYTES AND THEIR DISORDERS Similar to eosinophils and basophils, the lower reference limit for canine and feline monocyte numbers in peripheral blood is 0 or close to 0, so monocytopenia may be undetectable. Monocytosis can accompany a stress/corticosteroid response and can also be seen with inflammation. Monocytosis is expected with, but not restricted to, inflammatory processes requiring considerable phagocytic activity (e.g., immune-mediated hemolytic anemia or extensive necrosis); chronic situations; and those caused by foreign material or organisms that elicit granulomatous or pyogranulomatous inflammation. Monocytosis accompanied by cytopenias of other hemopoietic cell lines and aggressive phagocytosis of hemopoietic cells in peripheral blood, bone marrow, or other tissues could indicate monocyte neoplasia or hemophagocytic syndrome, a nonneoplastic proliferation of histiocytes

Answer 371

INTERPRETING THE LEUKOGRAM Excitement can lead to epinephrine release and movement of neutrophils from the marginating pool to the circulating pool. The net result of this shift is a relative increase in total WBC count attributable to an increase in the number of mature neutrophils. However, an epinephrine response does not necessarily produce an absolute neutrophilia since reference intervals have likely been established under similar circumstances.

Answer 372

Neutrophilia, lymphopenia Monocytosis. However, lymphopenia is the most consistent leukogram finding with stress, and is caused by altered movement of lymphocytes between the peripheral blood and lymph nodes, bone marrow, and other lymphocyte-rich tissues, coupled with lymphocyte lysis over the longer term. Whether neutrophilia and monocytosis also accompany a stress lymphopenia, may be dependent on the degree of corticosteroid elevation, duration, species, and presence or absence of concurrent illness.

Answer 373

Increased release from bone marrow; Decreased margination in peripheral blood; Decreased migration into tissues. Together, these result in neutrophilia, as noted on the CBC. Occasionally low numbers of band neutrophils are released from the bone marrow as well as mature neutrophils with stress. Administration of exogenous corticosteroids produces leukogram changes similar to the innate stress response, but may be more exaggerated and, therefore, more difficult to distinguish from an inflammatory leukogram. Additional clinical information and monitoring the leukogram over time are useful in differentiating these processes.

Answer 374

Exposure to lipopolysaccharide (LPS), a component of the cell wall of gram-negative bacteria, can result in endotoxemia. Endotoxemia causes widespread activation of inflammatory responses, sometimes leading to shock, organ failure, and suppression of wound healing processes. Neutrophils have heightened oxidative burst potential, become hyperadhesive to endothelium, and are unable to migrate across vascular endothelium into tissues to counter-invading organisms. Results are generalized endothelial damage, neutropenia, and thrombocytopenia on CBC results, and indicators of organ failure on additional laboratory tests.

Answer 375

Inflammation produces myriad leukogram changes reflecting the severity, extent of tissue involvement, duration, and offending agent. A grass awn lodged between the digits causes pustule formation and considerable discomfort, but is unlikely to result in leukogram abnormalities. The same grass awn migrating through the lung parenchyma may cause extensive tissue damage and inflammation, marked systemic effects, and usually severe leukogram changes.

Answer 376

The duration of the inflammation usually cannot be determined based on leukogram changes alone. Exceptions are acute, overwhelming inflammation and severe chronic inflammation. Most of the leukograms that clinical pathologists and clinicians confront are neither of these; therefore, establishing a timeframe is not possible. Acute mild inflammation can result in neutrophilia with a mild left shift (see Figure 193-2); however, leukograms representing recovery from acute, overwhelming inflammation and chronic inflammation can be identical at certain points in the process. Anatomic pathologists are better able to assess duration of inflammatory processes because the tissues being examined are the focal point of the reaction. Sampling the peripheral blood provides a window into only one component of a dynamic process. It is helpful to embrace the concept of this dynamic situation and consider the bone marrow and tissue environments when interpreting leukogram changes.

Answer 377

Acute, overwhelming inflammation as might occur with septic peritonitis caused by bowel perforation, would be expected to quickly deplete the peripheral blood of its neutrophils and the bone marrow of its postmitotic pool of neutrophils and bands (see Figure 193-2). Although neutrophil production is accelerated as a result of increased demand, the bone marrow is unable to meet these needs in the short term. The rapid movement of neutrophils into an extensive site of inflammation can result in a WBC count that is within reference intervals (WRI) or decreased. The leukocyte differential count is particularly important in these situations as immature neutrophilic granulocytes may equal or surpass the number of mature neutrophils, a situation that alerts the clinician to the fact that the inflammation is acute and overwhelming, and the bone marrow is not yet responding adequately to the tissue damage or infection. This left shift (presence of immature neutrophilic granulocytes in the peripheral blood) can be called degenerative if the absolute number of mature neutrophils is within or below the reference interval and immature neutrophilic granulocytes (e.g., bands, metamyelocytes, myelocytes) equal or surpass the mature stages in number. Toxic change is often recognized within mature and immature neutrophil cytoplasms in this situation

Answer 378

Toxic change results from accelerated granulopoiesis and is characterized by any of the following cytoplasmic changes: retention of primary, azurophilic granules; blue granularity due to ribosome retention; vacuolation; and Döhle bodies, which are deposits of rough endoplasmic reticulum. Although these features can occur in any combination, often the type of toxic change that is present is relatively consistent within that sample. Evaluation of canine and feline blood smears for toxic change in neutrophils provides useful clinical information and aids in prognostication

Answer 379

Severe inflammation of longer duration than the situation of acute bowel perforation described above may be characterized by a severe left shift. However, the total leukocyte count is often increased due to increased mature and immature neutrophilic granulocytes. Pyometra is an example of such a pathologic process. Although there is a severe left shift suggesting the bone marrow is not entirely capable of meeting the demands for neutrophils, bone marrow examination would reveal granulocytic hyperplasia. Also, when the focus of tissue demand, the uterus in this example, is removed, a marked rebound neutrophilia is often seen and several days may pass before neutrophils return to normal numbers and immature neutrophils disappear from the peripheral circulation.

Answer 380

Chronic inflammatory processes can produce variable leukogram changes reflecting the nature of the offending agent, the surface area involved, and the host response. Moderate to severe neutrophilia, with a mild or no left shift and moderate to marked monocytosis, are the classic findings with chronic inflammation (see Figure 193-2). However, a long-standing, well–walled-off abscess may produce subtle to no leukogram changes.

Answer 381

Neutropenia without a left shift or toxic change is not usually explained by an inflammatory process. Mild neutropenia could represent normal fluctuation in a clinically healthy animal. However, persistent moderate to severe neutropenia may signal bone marrow pathology.

Answer 382

Canine leukocyte adhesion deficiency (CLAD) is a rare hereditary disease affecting Irish Setter dogs, Irish Setter–cross dogs and Irish Red and White Setter dogs. The disease is characterized by recurrent bacterial infections beginning shortly after birth, often including omphalophlebitis, gingivitis, and pyoderma. The marked leukocytosis seen on CBC is due to the inability of neutrophils to adhere to and transmigrate the vascular endothelium, migrate to infection sites in tissues, and phagocytose bacteria. The defect is caused by a missense mutation in the gene encoding β-2 integrin, the CD18 subunit of several heterodimeric leukocyte adhesion proteins. As an autosomal recessive inherited disease, carrier dogs are not clinically affected whereas homozygotes for the mutation experience serious infections that significantly shorten their lives even with antibiotic therapy and other supportive care. The disease has been successfully treated using a foamy virus vector expressing canine CD18.

Answer 383

Chédiak-Higashi syndrome is a rare autosomal recessive condition reported in several species, including Blue Smoke Persian cats. The syndrome is characterized by hypopigmentation of skin, eyes, and hair; superficial bleeding; and variable susceptibility to infections. Large peroxidase-positive cytoplasmic granules containing lysosomal enzymes are present in most nucleated cells, including neutrophils (Web Figure 193-2).

Answer 384

Cyclic Hemopoiesis Cyclic hemopoiesis is a rare stem cell disorder with autosomal recessive inheritance in gray Collie dogs. Affected dogs experience cyclic fluctuations in production of all hemopoietic cells and maturation arrest and apoptosis of developing marrow cells at the onset of neutropenia. Neutrophil numbers decline every 10 to 12 days, followed by rebound. Increased susceptibility to infections correlates with episodes of neutropenia.

Answer 385

Neutrophil Anomaly of Birman Cats An inherited anomaly of neutrophil granulation and staining has been identified in Birman cats as an autosomal recessive trait. Affected cats are clinically healthy but their neutrophils contain reddish-purple cytoplasmic granules with Romanowsky stains

Answer 386

Pelger-Huët anomaly is an inherited disorder of leukocyte and megakaryocyte development that has been identified in many species, including dogs and cats. The characteristic finding in neutrophils, eosinophils, and basophils is hyposegmentation of the nucleus, but chromatin is coarse and clumped and cytoplasmic features are normal. Although not of clinical significance in heterozygotes, peripheral blood findings can initially be misinterpreted as a severe left shift suggestive of inflammation. The lack of cytoplasmic abnormalities (toxic change) in neutrophils and persistence of the abnormal nuclear features in the healthy animal help to distinguish between inflammation and Pelger-Huët anomaly. Transient hyposegmentation of leukocytes, sometimes referred to as pseudo-Pelger-Huët anomaly, may occur with inflammation, neoplasia, or drug therapy and can usually be differentiated from Pelger-Huët anomaly by monitoring of the CBC and identifying an underlying condition Probably inherited.

Answer 387

Naturally occurring lysosomal storage diseases are reported in animals, and although affected cats and dogs may appear healthy at birth, the progressive accumulation of nondegraded substrate in lysosomes can lead to skeletal abnormalities, growth retardation, organomegaly, and visual defects. The presence of abnormal cytoplasmic granules or vacuoles in peripheral blood leukocytes is suggestive of one of many types of lysosomal storage diseases. The mucopolysaccharidoses are inherited lysosomal storage diseases caused by deficiency of one of several glycosaminoglycan (GAG)-degrading enzymes. Specific metabolic, enzymatic, or molecular evaluation is needed to diagnose these storage diseases. For those diseases with known mutations in the gene encoding the defective enzyme, DNA-based testing is available. Genetic studies indicate that most of these diseases are inherited as an autosomal recessive trait

Answer 388

Infectious Agents as Inclusions in Peripheral Blood Leukocytes Thorough peripheral blood smear evaluation may provide an etiologic diagnosis when disease is caused by certain viral, bacterial, yeast, or parasitic organisms. Such examples include canine distemper virus inclusion bodies in neutrophils and erythrocytes; bacterial infections resulting in bacteremia or septicemia; Anaplasma phagocytophilium infection in dogs; Histoplasma capsulatum yeast infections; and Hepatozoon americanum, an apicomplexan parasite

Answer 389

Congestion, lymphoid hyperplasia, capsulitis, extramedullary hematopoiesis hyperplastic nodules accounted for more than 50% of the cats with nonneoplastic splenic disease.

Answer 390

Common complaints include vomiting, anorexia, weakness, collapse, abdominal enlargement, and weight loss. Polyuria and polydipsia may occur; the mechanism is unclear, but it resolves after splenectomy. Clinical signs are usually related to abdominal distention from a mass, uniform splenomegaly or intraabdominal bleeding. Lethargy and collapse may occur due to hypovolemia, arrhythmias, or anemia.

Answer 391

Erythrocyte counts are usually normal or decreased, but can be increased in patients with splenomegaly associated with polycythemia vera. Schistocytosis, which is highly indicative of a neoplastic splenic disorder, was observed in 23% of patients with splenic tumors, but only in 3% of dogs with nonneoplastic disease. Granulocyte and platelet counts also can be decreased, normal, or increased

Answer 392

Extramedullary hematopoiesis can occur in the spleen. Because the spleen maintains the ability for hematopoiesis but does not retain the normal inhibitory mechanisms present in the bone marrow, it releases young blood cells into the circulation. Increases in nucleated red blood cells and immature white blood cells (leukoerythroblastic effect) may appear in the peripheral blood in patients with splenic disorders.

Answer 393

Cats with splenomegalic need be tested for infection with feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV).

Answer 394

In dogs, around two thirds of splenic masses are diagnosed pathologically as neoplastic. In cats, around one half of splenic lesions submitted for pathologic examination are diagnosed as neoplastic. Tumors of the spleen usually present either as localized or diffuse splenomegaly and can be confused with nonneoplastic conditions. The actual clinical features of primary splenic tumors can be very vague, except in cases of splenic rupture and bleeding.

Answer 395

Hemangiosarcoma is a highly malignant tumor arising from the vascular endothelium. The most common primary site of hemangiosarcoma in the dog is the spleen, but it can also affect cutaneous sites. Around 25% of dogs with splenic hemangiosarcoma also have concurrent hemangiosarcoma affecting the right atrium. The classical presentation of hemangiosarcoma in dogs is that of a solitary cavitated lesion that bleeds causing hemoperitoneum and sudden-onset hypovolemic collapse. Abdominocentesis reveal frank hemorrhage. If possible, platelet count and clotting profile should be performed. Approximately 50% of dogs that present with abdominal bleeding are in DIC. Anemia and thrombocytopenia are common. Reticulocytosis and polychromasia may occur depending on when the bleed took place. A peripheral blood smear may reveal schistocytosis as red cells shear as they course through the tortuous lesion in the spleen.

Answer 396

Dogs with hemoperitoneum and concurrent hematologic changes such as schistocytosis and thrombocytopenia with concurrent anemia should carry a high suspicion for hemangiosarcoma. The only way to definitively diagnose hemangiosarcoma is by histopathology following splenectomy. Cytology is often unrewarding, and the gross appearance of the spleen is often a poor indicator of the underlying disease.

Answer 397

Nonangiomatous, Nonlymphoid Sarcomas of the Spleen Fibrosarcoma, leiomyosarcoma, myxosarcoma, osteosarcoma, liposarcoma, and undifferentiated sarcoma have all been described as primary splenic malignant tumors. Unlike hemangiosarcoma, the clinical signs associated with these tumors are usually vague and typically involve progressive anorexia and lethargy. In rare cases where the tumor has become large, it may result in splenic torsion.

Answer 398

Canine histiocytic disorders represent a range of diseases that are a diagnostic and therapeutic challenge. This disease is most common in the Bernese Mountain Dog and Retriever breeds, but has been reported in a number of other breeds. The spleen can be a site for primary histiocytic sarcoma or a site of dissemination from malignant histiocytosis. Primary splenic histiocytic sarcoma has been associated with a hemophagocytic syndrome characterized by a Coombs’-negative anemia due to erythrophagia by malignant histiocytes. Whether primary or part of a secondary disease complex, histiocytic disease associated with the spleen carries a poor prognosis. Dogs will often die from disseminated disease even after splenectomy.

Answer 399

A number of benign tumors have been reported in the canine spleen. In general, these carry a good prognosis with long survival times following splenectomy. Myelolipomas are tumors containing a mixture of adipose tissue and hematopoietic tissue. Lipomas are benign fat tumors that may affect the spleen. Hemangiomas are benign tumors arising from the vasculature. They can be distinguished from hemangiosarcoma only on histopathology. Splenectomy is considered curative.

Answer 400

Metastatic Tumors of the Canine Spleen As well as being a site for primary neoplasia, the spleen is also a site for secondary tumor deposits or infiltrates. Notable among these are lymphoma, leukemias, multiple myeloma, primary erythrocytosis (polycythemia vera), high-grade metastatic mast cell tumors, and carcinomas. The management of secondary splenic tumors revolves around management of the underlying primary malignancy and usually involves systemic chemotherapy.

Answer 401

Malignant Tumors of the Feline Spleen Mast Cell Tumor In cats, the spleen is a common site for primary mast cell tumor. Typically, these patients present with a history of dullness and lethargy, progressive anorexia, occasional vomiting (histamine release), and diffuse splenomegaly on clinical examination. Mastocytosis is observed on a complete blood count, whereas malignant mast cells can be seen in lymph nodes, liver, and bone marrow. Diagnosis is usually made by ultrasound-directed fine needle aspirate of the spleen. The treatment of choice is splenectomy, with a mean survival time of around 12 to 18 months following surgery. However, this is a high-risk surgery because excessive handling of the spleen could lead to massive histamine and heparin release leading to shock and ultimately death. Presurgical therapy with antihistamines, careful surgical technique, and proper anesthetic monitoring are essential for success. Following surgery the mastocytosis usually clears without any chemical therapy. Adjunctive use of chemotherapy is controversial with no large-scale clinical studies proving their benefit.

Answer 402

Compared to the canine disease, feline splenic hemangiosarcoma is rare. As with dogs, other primary sarcomas (e.g., fibrosarcoma) have been reported but are very rare. A number of benign tumors have been reported in the feline spleen. The feline spleen can be a site for both primary neoplasia and for secondary tumor deposits or infiltrates. Notable amongst these are lymphoma, leukemias, multiple myeloma (rare in cats), and carcinomatosis.

Answer 403

Generalized splenomegaly occurs not only with tumor infiltration, but also may be caused by congestion, splenic hyperplasia/extramedullary hematopoiesis, inflammation, or cellular infiltration. Splenic masses are usually due to neoplasia, hematoma, abscess, or nodular hyperplasia

Answer 404

Congestion is commonly seen as a consequence to sedation or anesthesia, portal hypertension, or splenic vein thrombosis. Administration of phenothiazine sedatives (e.g., acepromazine) or ultrashort acting barbiturates (e.g., thiopental) produces substantial splenomegaly. Splenomegaly can be severe, because up to 30% of the blood volume can be pooled in the spleen. (Administration of propofol to dogs, however, did not produce statistically significant splenomegaly)

Answer 405

Congestion can also be secondary to portal hypertension with hepatic disease and systemic venous hypertension in right-sided heart failure or intrathoracic caudal vena cava compression. Chronic congestion of the spleen may lead to splenic hyperplasia. No changes in echogenicity were subjectively noted in congested spleens, although significant increased attenuation and a trend towards increased backscatter (echogenicity) were noted. Diffuse changes in splenic echogenicity in patients with a known cause of congestion, therefore, are likely due to another underlying condition.

Answer 406

Splenic pedicle torsion is a special cause of congestion in dogs. It usually develops in large, deep-chested dogs, especially the German Shepherd and Great Dane. Acute torsion causes profound systemic signs with shock and abdominal discomfort, whereas chronic torsion is associated with vague signs including vomiting, anorexia, lethargy, and icterus. In one study, intravascular thrombi could be identified in 50% of the cases. Supportive therapy should be instituted immediately in these patients and the spleen removed surgically. If appropriately treated, splenic torsion carries a favorable prognosis

Answer 407

Infarcts can be observed in patients in hypercoagulable states associated with liver disease, renal disease, or hyperadrenocorticism. It also can occur with preexisting uniform splenomegaly or splenic torsion. Splenic infarction is a sign of abnormal coagulation or blood flow, and the clinical signs are related to the underlying cause.

Answer 408

The splenomegaly seen with splenic hyperplasia and extramedullary hematopoiesis reflects “work hypertrophy” resulting from removal of abnormal blood cells from circulation, increased activity of mononuclear phagocytic and lymphoid cells, and increased blood cell production. In immune-mediated hemolytic anemia and thrombocytopenia, the spleen serves as a site of antibody production and also as an important site of removal of antibody-sensitized cells. Chronic increased destruction of red blood cells in some non–immune-mediated hemolytic diseases also appears to cause hyperplastic splenomegaly in dogs and cats In immune-mediated hemolytic anemia and thrombocytopenia, the spleen serves as a site of antibody production and also as an important site of removal of antibody-sensitized cells. Chronic increased destruction of red blood cells in some non–immune-mediated hemolytic diseases also appears to cause hyperplastic splenomegaly in dogs and cats. Chronic antigen stimulation by infectious agents (e.g., bacterial endocarditis), blood parasites, or immune-mediated disease can stimulate hyperplasia of mononuclear phagocytic and lymphoid cells. In work hypertrophy, the spleen is uniformly enlarged and may be hypoechoic on ultrasonographic examination. Cytologically, small lymphocytes still predominate, but there is an increase in medium- and large-sized lymphocytes, and plasma cells are commonly observed. Extramedullary hematopoiesis (EMH) may accompany splenic hyperplasia in patients with concomitant anemia, thrombocytopenia, or leukopenia. It is a very common cytologic diagnosis in dogs with uniform splenomegaly and may also occur with a variety of splenic neoplasms. EMH is also common in cats. A nodular pattern is more common in cats with EMH. The presence of nucleated red blood cells in peripheral blood suggests EMH. Cytologically, precursors of all three cell lines may be observed in this condition.[15] A finding of hematopoietic precursors with large amount of vacuoles in the background suggest the presence of a myelolipoma rather than EMH

Answer 409

Nodular hyperplasia is a nonneoplastic regional proliferation of components cells normally found in the parenchyma of the canine spleen. Nodular hyperplastic lymphoid proliferation is the most common form in dogs, but it is not common cats. A high percentage of splenic lesions in dogs have features of hematomas and nodular hyperplasia, which suggests that these disorders may be different stages of the same process. Cats have a “nonsinusal” type of spleen and a different architecture and blood flow pattern of the intermediate circulation bordering the white pulp. Those differences could render the feline spleen less vulnerable to disrupted blood flow and hematoma formation. Nodular hyperplastic lesions are usually hypoechoic on ultrasonographic examination. Splenic hematomas in dogs are associated with large splenic masses. Large hyperplastic nodules and splenic hematoma cannot be differentiated from hemangiosarcoma grossly. A particular variation of hyperplastic nodule in dogs is the fibrohistiocytic nodule. Nodular fibrohistiocytic proliferation is characterized by a mixed population of histiocytoid or spindle cells intertwined with hematopoietic elements, plasma cells, and lymphocytes.

Answer 410

Inflammatory splenomegaly (splenitis) is a uniform splenomegaly usually secondary to infection. In addition to the inflammatory response associated with hyperplasia, patients with splenitis also have increases in other inflammatory cells. It is important to classify the splenitis according to the predominant cell type, because different etiologic agents are associated with different types of inflammation. Some overlap exists, and the same organism can cause a different inflammatory response in a different patient. For example, lymphoplasmacytic splenitis has been observed in patients with feline infectious peritonitis, histoplasmosis, and blastomycosis.

Answer 411

Splenic nodules without associated splenomegaly are a relatively common finding in older dogs undergoing abdominal ultrasound for unrelated reasons. Most splenic nodules in this age group are benign and might require no further action. Myelolipomas can be easily identified, whereas lymphoid hyperplasia, EMH, and splenic infarcts may be more difficult to differentiate from an early neoplastic lesion

Hematology and Immunology Flashcards

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