WBC Disorders

Question 1

Basic principles of Leukopenia and Leukocytosis

Answer 1

Hematopoeisis occurs via a step wise maturation of CD34+ hematopoietic stem cells

Cells mature and are released from the bone marrow into the blood

A normal WBC count is approx 5-10 K/microL

• a low WBC count = leukopenia
• a high WBC count = leukocytosis
• a low or high WBC count is usually due to a decrease or increase in one particular cell lineage

Question 2

Neutropenia

Answer 2

Neutropenia refers to a decreased number of circulating neutrophils

Causes

• drug toxicity (eg chemo with alkylating agents) –> damage to stem cells results in decreased production of WBCs, especially neutrophils
• severe infection (eg gram neg sepsis) –> increased movement of neutrophils into tissues results in decreased circulating neutrophils
• as a treatment, GM-CSF or G-CSF may be used to boost granulocyte production, thereby decreasing risk of infection in neutropenic

Question 3

Lymphopenia

Answer 3

Decreased number of circulating lymphocytes

Causes

• Immunodeficiency (eg DiGeorge syndrome or HIV)
• high cortisol state –> induces apoptosis of lymphocytes
• autoimmune destruction (eg SLE)
• whole body radiation –> lymphocytes are highly sensitive to radiation –> lymphopenia is the earliest change to emerge after whole body radiation

Question 4

Causes of neutrophilic leukocytosis

Answer 4

• bacterial infection or tissue necrosis –> induces release of marginated pool and bone marrow neutrophils, including immature forms (left shift); immature cells are characterized by decreased Fc receptors (CD16)
• high cortisol state –> impairs leukocyte adhesion = release of marginated pool of neutrophils

Question 5

Causes of monocytosis

Answer 5

• chronic inflammatory states (autoimmune or infectious)

- malignancy

Question 6

Causes of eosinophila

Answer 6

• allergic reactions (type I hypersensitivity)
• parasitic infections
• Hodgkins lymphoma

eosinophila is driven by increased eosinophil chemotactic factor

Question 7

Causes of basophila

Answer 7

Classically seen in CML

Question 8

Causes of lymphocytic leukocytosis

Answer 8

• viral infections –> T lymphocytes undergo hyperplasia in response to virally infected cells
• bordetella pertussis infection –> bacteria produce lymphocytosis promoting factor –> blocks circulating lymphocytes from leaving the blood to enter the lymph node

Question 9

Infectious Mononucleosis

Answer 9

EBV infection that results in a lymphocytic leukocytosis comprised of reactive CD8 T cells
- CMV is a less common cause

EBV primarily infects:

• oropharynx –> results in pharyngitis
• liver –> results in hepatitis with hepatomegaly and elevated liver enzymes
• B cells

CD8 T cell response leads to:

• generalized lymphadenopathy due to T cell hyperplasia in the lymph node paracortex
• splenomegaly due to T-cell hyperplasia in the periarterial lymphatic sheath
• high WBC count with atypical lymphocytes (reactive CD8 T cells) in the blood

Monospot test is used for screening

• detects IgM antibodies that cross-react with horse or sheep RBCs = heterophile antibodies
• usually turns positive within 1 week after infection
• a neg monospot test suggests CMV as a possible cause of mono
• definitive diagnosis is made by serologic testing for the EBV viral capsin antigen

Question 10

Complications of mono

Answer 10

• increased risk for splenic rupture –> patients are advised to avoid contact sports for one month
• rash if exposed to ampicillin
• dormancy of virus in B cells leads to increased risk for both recurrence and b-cell lymphoma, especially if immunodeficiency develops

Question 11

Basic principles of acute leukemia

Answer 11

Neoplastic proliferation of blasts –> defined as the accumulation of >20% blasts in the bone marrow
- increased blasts crowd out normal hematopoiesis, resulting in an “acute” presentation with anemia (fatigue), thrombocytopenia (bleeding), or neutropenia “infection”

Blasts usually enter the blood stream –> results in a high WBC
- blasts are large, immature cells, often with punched out nucleoli

Question 12

Acute lymphoblastic leukemia (ALL)

Answer 12

Neoplastic accumulation of lymphoblasts (>20%) in the bone marrow

• lymphoblasts are characterized by positive nuclear staining for TdT = a DNA polymerase
• TdT is absent in myeloid blasts and mature lymphocytes

Most commonly arises in children –> associated with Down syndrome (usually after the age of 5)

Subclassified into B-ALL and T-ALL based on surface markers

Question 13

B-ALL

Answer 13

Most common type of ALL

• usually characterized by lymphoblasts (TdT+) that express CD10, CD19 and CD20
• excellent response to chemo –> requires prophylaxis to scrotum and CSF

Prognosis is based on cytogenetic abnormalities

• t(12;21) –> good prognosis, more commonly seen in children
• t(9;22) –> poor prognosis, more commonly seen in adults (Ph+)

Question 14

T-ALL

Answer 14

Characterized by lymphoblasts (TdT+) that express markers ranging from CD2-CD8
- blasts do not express CD10

Usually presents in teenagers as a mediastinal (thymic) mass –> called acute lymphoblastic lymphoma because the malignant cells for a mass

Question 15

Acute myeloid leukemia

Answer 15

Neoplastic accumulation of immature myeloid cells (>20%) in the bone marrow

• myeloblasts are usually characterized by positive cytoplasmic staining for myeloperoxidase
• crystal aggregates of MPO may be seen as Auer rods

Most commonly arises in older adults (50-60 yrs)

Subclassified based on cytogenetic abnormalities, lineage of myeloblasts, and surface markers

Question 16

Subtypes of AML

Answer 16

1. Acute promyelocytic leukemia = characterized by t(15;17) –> involves translocation of the RAR on chromosome 17 to chromosome 15
   - RAR disruption blocks maturation and promyelocytes accumulate
   - abnormal promyelocytes contain numerous primary granules that increase the risk for DIC
   - treatment is with all-trans-retinoic acid (ATRA) –> binds the altered receptor and causes the blasts to mature
2. Acute monocytic leukemia = proliferation of monoblasts, usually lack MPO
   - blasts characteristically infiltrate gums
3. Acute megakaryoblastic leukemia = proliferation of megakaryoblasts –> lack MPO
   - associated with Down syndrome (usually before the age of 5)

Question 17

Myelodysplastic syndromes

Answer 17

May give rise to AML, especially with prior exposure to alkylating agents or radiotherapy

• myelodysplastic syndromes usually present with cytopenias, hypercellular bone marrow, abnormal maturation of cells, and increased blasts (<20%)
• most patients die from infection or bleeding, though some progress to acute leukemia

Question 18

Basic principles of chronic leukemia

Answer 18

Neoplastic proliferation of mature circulating lymphocytes –> characterized by a high WBC count
- usually insidious in onset and seen in older adults

Question 19

Chronic lymphocytic leukemia

Answer 19

Neoplastic proliferation of naive B cells that co-express CD5 and CD20

• most common leukemia overall
• increased lymphocytes and smudge cells are seen on blood smear
• involvement of lymph nodes leads to generalized lymphadenopathy –> called small lymphocytic lymphoma

Complications

• hypogammaglobulinemia –> infection is the most common cause of death
• autoimmune hemolytic anemia
• transformation to diffuse large B cell lymphoma –> marked clinically by an enlarging lymph node of spleen

Question 20

Hairy cell leukemia

Answer 20

Neoplastic proliferation of mature B cells characterized by hairy cytoplasmic processes

• cells are positive for tartrate resistant acid phosphatase (TRAP)
• clinical features include splenomegaly (due to accumulation of hairy cells in the red pulp) and “dry tap” on bone marrow aspiration (due to marrow fibrosis)
• lymphadenopathy is usually absent

Excellent response to cladribine = adenosine deaminase inhibitor –> adenosine accumulates to toxic levels in neoplastic B cells

Question 21

Adult T cell leukemia/lymphoma

Answer 21

Neoplastic proliferation of mature CD4 T cells

• associated with HTLV-1
• most commonly seen in Japan and the caribbean

Clinical features

• rash (skin infiltration)
• generalized lymphadenopathy with hepatosplenomegaly
• lytic bone lesions with hypercalcemia

Question 22

Mycosis fungoides

Answer 22

Neoplastic proliferation of mature CD4+ T cells that infiltrate the skin, producing localized skin rash, plaques, and nodules
- aggregates of neoplastic cells in the epidermis = pautrier microabscesses

Cells can spread to involve the blood –> called Sezary syndrome
- characteristic lymphocytes with cerebriform nuclei are seen on blood smears

Question 23

Basic principles of myeloproliferative disorders

Answer 23

Neoplastic proliferation of mature cells of myeloid lineage

• disease of late adulthood (avg age 50-60 years)
• results in high WBC count with hypercellular bone marrow
• cells of all myeloid lineages are increased –> classified based on the dominant myeloid cell produced

Complications

• increased risk for hyperuricemia and gout due to high turnover of cells
• progression to marrow fibrosis or transformation to acute leukemia

Question 24

Chronic myeloid leukemia

Answer 24

Neoplastic proliferation of mature myeloid cells, especially granulocytes and their precursors
- basophils are characteristically increased

Driven by t(9;22) = philadelphia chromosome –> generates a BCR-ABL fusion protein with increased TK activity
- first line treatment is imatinib –> blocks TK activity

Splenomegaly is common –> enlarging spleen suggests progression to accelerated phase of disease –> transformation to acute leukemia usually follows shortly thereafter
- can transform to AML (2/3) of cases or ALL (1/3 of cases) since mutation is in a pluripotent stem cells

Question 25

How to distinguish CML from a leukemoid reaction (reactive neutrophilic leukocytosis)

Answer 25

1. Negative leukocyte alkaline phosphatase (LAP) stain --> granulocytes in a leukemoid reaction are LAP positive 2. Increased basophils --> absent with leukemoid reaction 3. t(9;22) --> absent in leukemoid reaction

Question 26

Polycythemia vera

Answer 26

Neoplastic proliferation of mature myeloid cells, especially RBCs --> granulocytes and platelets are also increased - associated with JAK2 mutation Clinical symptoms mainly due to hyperviscosity of blood - blurry vision and headache - increased risk of venous thrombosis (hepatic vein, portal vein, and dural sinus) - flushed face due to congestion - itching, especially after bathing (due to histamine release from increased mast cells) Treatment --> phlebotomy, hydroxyrea - without tx, death usually occurs within 1 year

Question 27

How to distinguis PV from reactive polycythemia

Answer 27

n PV, EPO levels are decreased and SaO2 is normal - in reactive polycythemia due to high altitude or lung disease, SaO2 is low and EPO is increased - in reactive polycythemia due to ectopic EPO production from renal cell carcinoma, EPO is high and SaO2 is normal

Question 28

Essential thrombocytopenia

Answer 28

Neoplastic proliferation of mature myeloid cells, especially platelets - RBCs and granulocytes are also increased - associated with JAK2 kinase mutation Symptoms are related to an increased risk of bleeding and/or thrombosis - rarely progresses to marrow fibrosis or acute leukemia - no significant risk for hyperuricemia or gout

Question 29

Myelofibrosis

Answer 29

Neoplastic proliferation of mature myeloid cells, especially megakaryocytes - associated with JAK2 kinase mutation - megakaryocytes produce excess PDGF --> causes marrow fibrosis Clinical features - splenomegaly due to extramedullary hematopoiesis - leukoerythroblastic smear = tear drop RBCs, nucleated RBCs, and immature granulocytes - increased risk of infection, thrombosis and bleeding

Question 30

Lymphadenopathy

Answer 30

LAD refers to enlarged lymph nodes - painful LAD is usually seen in lymph nodes that are draining a region of acute infections = acute lymphadenitis - painless LAD can be seen with chronic inflammation (chronic lymphadenitis), metastatic carcinoma, or lymphoma In inflammation, lymph node enlargement is due to hyperplasia of particular regions of the lymph node - follicular hyperplasia (B-cell region) --> seen with rheumatoid arthritis and early stages of HIV, for example - paracortex hyperplasia --> seen with viral infections - hyperplasia of sinus histiocytes --> seen with lymph nodes that are draining a tissue with cnacer

Question 31

Basic principles of lymphoma

Answer 31

Neoplastic proliferation of lymphoid cells that forms a mass --> may arise in a lymph node or in extranodal tissue Divided into non-Hodgkin lymphoma and Hodgkin lymphoma NHL is further classified based on cell type (B vs. T), cell size, patterns of cell growth, expression of surface markers, and cytogenetic translocations - small B cells = follicular lymphoma, mantle cell lymphoma, marginal zone lymphoma, and small lymphocytic lymphoma (CLL that involves tissue) - intermediate sized B cells = Burkitt lymphoma - large B cells = diffuse large B cell lymphoma

Question 32

Follicular lymphoma

Answer 32

Neoplastic proliferation of small B cells (CD20+) that form follicle like nodules - presents in late adulthood with painless lymphadenopathy - driven by t(14;18) --> BCL2 on chromsome 18 translocates to the Ig heavy chain locus on chromosome 14 - results in overexpression of Bcl2 = inhibits apoptosis Treatment is reserved for patients who are symptomatic --> involves low dose chemo or rituximab Progression to diffuse large B cell lymphoma is an important complication --> presents as an enlarging lymph node

Question 33

How to distinguish follicular lymphoma from reactive follicular hyperplasia

Answer 33

1. Disruption of normal lymph node architecture --> maintained in normal follicular hyperplasia 2. Lack of tingible body macrophages in germinal centers --> present in follicular hyperplasia 3. Bcl2 expression in follicles --> not expressed in follicular hyperplasia 4. Monoclonality --> follicular hyperplasia is polyclonal

Question 34

Mantle cell lymphoma

Answer 34

Neoplastic proliferation of small B cells (CD20+) that expands the mantle zone - presents in late adulthood with painless lymphadenopathy - drived by t(11;14) --> cyclin D1 gene on chromosome 11 translocates to Ig heavy chain locus on chromosome 14 - over expression of cyclin D1 promotes G1/S transition in the cell cycle, facilitating neoplastic proliferation

Question 35

Marginal zone lymphoma

Answer 35

Neoplastic proliferation of small B cells (CD20+) that expands the marginal zone - associated with chronic inflammatory states such as hashimotos, sjogren syndrome, and h. pylori gastritis - the marginal zone is formed by post-germical center B cells - MALToma is marginal zone lymphoma in mucosal sites - gastric MALToma may regress with treatment of H. pylori

Question 36

Burkitt lymphoma

Answer 36

Neoplastic proliferation of intermediate sized B cells (CD20+) --> associated with EBV - classically presents as an extranodal mass in a child or young adult - african form usually involves the jaw - sporadic form usually involves the abdomen Driven by translocations of c-myc (chrom. 8) - t(8;14) is most common --> results in translocation of c-myc to the Ig heavy chain - overexpression of c-myc oncogene promotes cell growht = transcription activator Characterized by high mitotic index + starry sky appearance on microscopy

Question 37

Diffuse large B cell lymphoma

Answer 37

Neoplastic proliferation of large B cells (CD20+) that grow diffusely in sheets - most common form of NHL - clinically aggressive --> high grade Arises sporadically or from transformation of a low grade lymphoma (eg follicular lymphoma) - presents in late adulthood as an enlarging lymph node or an extranodal mass

Question 38

Hodgkin Lymphoma

Answer 38

Neoplastic proliferation of Reed-Sternberg cells = large B cells with multi-lobed nuclei and prominent nucleoli (owl eyed nuclei) --> classically positive for CD15 and CD30 RS cells secrete cytokines - occasionally results in B symptoms --> fever, chills, weight loss, and night sweats - attracts reactive lymphocytes, plasma cells, macrophages and eosinophils - may lead to fibrosis Reactive inflammatory cells make up a bulk of the tumor and form the basis for classification of HL

Question 39

Subtypes of Hodgkin lymphoma

Answer 39

1. Nodular sclerosing = most common subtype --> 70% of all cases - classic presentation is an enlarging cervical or mediastinal lymph node in a young adult, usually female - lymph node is divided by bands of sclerosis --> RS cells are present in lake like spaces (lacunar cells) 2. Lymphocyte rich --> has best prognosis 3. Mixed cellularity --> often associated with abundant eosinophils (RS cells produce IL-5) 4. Lymphocyte depleted --> most aggressive type, usually seen in the elderly and HIV positive people

Question 40

Multiple myeloma

Answer 40

Malignant proliferation of plasma cells in the bone marrow - most common primary malignancy of bone --> metastatic cancer is the most common malignant lesion of bone overal - high serum IL-6 may be present --> stimulates plasma cell growth and immunoglobulin production

Question 41

Clinical features of multiple myeloma

Answer 41

1. Bone pain with hypercalcemia --> neoplastic cells activate the RANK receptor on osteoclasts, leading to bone destruction - lytic, pumched out skeletal lesions are seex on x ray, especially in the vertebrae and skull - increased risk for fracture 2. Elevated serum protein --> neoplastic plasma cells produce immunoglobulin - M spike is present on serum protein electrophoresis (SPEP) --> most commonly due to IgG or IgA 3. Increased risk of infection --> monoclonal antibody lacks antigenic diversity - infection is the most common cause of death 4. Rouleaux formation of RBCs on blood smear --> increased serum protein decreases charge between RBCs and they aggregate 5. Primary AL amyloidosis --> free light chains circulate in serum and deposit in tissues 6. Proteinuria --> free light chain is excreted in the urine as bence jones protein - deposition in kidney tubules leads to risk for renal failure (myeloma kidney)

Question 42

Monoclonal gammopathy of undetermined significants (MGUS)

Answer 42

Increased serum protein with M spike on SPEP --> other features of multiple myeloma are absent (no lytic bone lesions, hypercalcemia, AL amyloid, or bence jones proteinuria) - common in elderly (seen in 5% of 70 year old people) --> 1% of patients with MGUS develop multiple myeloma each year

Question 43

Waldenstrom macroglobulinemia

Answer 43

B cell lymphoma with monoclonal IgM production Clinical features - generalized lymphadenopathy - lytic bone lesions are absent - increased serum protein with M spike (comprised of IgM) - visual and neurologic deficits (e.g. retinal hemorrhage or stroke) - IgM = large pentamer, causes serum hyperviscosity - bleeding --> viscous serum results in defective platelet aggregation Acute complications are treated with plasmapheresis --> removes IgM from the serum

Question 44

Langerhans cell histiocytosis

Answer 44

Langerhans cells are specialized dendritic cells found predominantly in the skin - derived from bone marrow monocytes - present antigen to naive T cells Langerhans cell histiocytosis is a neoplastic proliferation of Langerhans cells - characteristic Birbeck granules (tennis racket) are seen on electron microscopy - cells are CD1a and S1)) positive by immunohistochemistry