Platelet disorders

Question 1

Potential mechanisms of ITP

Answer 1

1. Dysregulation of T-cells that has direct cytotoxic effect of plt and megakaryocytes
2. Autoantibodies against glycoproteins on megakaryocytes impairing megakaryocyte proliferation and platelet production
3. Autoantibodies against glycoproteins on platelets (GPIIb-IIIa, GPIb-IX) resulting in increased clearance by R.E.S.
4. Platelet opsonization
5. Decreased levels of regulatory T cells activity

Question 2

Explain FNAIT. What is the most common antigen target on platelets. One feature that distinguishes from HDFN.

Answer 2

FNAIT= Maternal IgG antibody against paternal antigen on fetal platelets. Antibody crosses placenta leading to opsonization and destruction of fetal platelets

Most common: mom HPA 1b/1b (2% of population)
dad HPA 1a/1a
baby has HPA 1a on its platelets
Less common: HPA 5b (whites), HPA-4b (asians), HPA-3b

*NAIT can occur with the first pregnancy, HDN only occurs in the subsequent pregnancy.

Question 3

MOA of the following anti-platelets:
ASA, Abciximab, Prasugrel, Ticagrelor.

Answer 3

a. Ticagrelor: Reversibly inhibits ADP P2Y12 receptor for ADP → inhibits ADP-dependent and TXA2 platelet aggregation
b. Prasugrel, plavix: Same as above but irreversible
c. Abciximab: Inhibits GPIIbIIIa → fibrinogen can’t bind → inhibits platelet aggregation
d. ASA: COX 1 inhibitor–>blocks TxA2–>less aggregation

Question 4

What’s the evidence for EC-ASA in secondary prevention of VTE?

Answer 4

WARFASA
ASA 100mg OD vs placebo for patients who completed 6-18mo of OAC for VTE
Primary outcome: recurrent VTE
Outcome: 6.6% vs 11.2%

ASPIRE
ASA 100mg OD vs placebo for patients who completed 1.5-24mo of OAC
Primary outcome: recurrent VTE
Outcome: 14% vs 18%

Pooled analysis of the two trials showed a 32% reduction in VTE recurrence (HR 0.68; P=0.007)

Question 5

Name 4 MYH9 disorders

Answer 5

May-Hegglin- Just heme features
Epstein Syndrome- No dohle-body inclusions
Fetchner syndrome=fucked, all features.
Sebastian’s Syndrome

• MYH9 encodes non-muscle myosin Ia heavy chain
• Morph- Dohle-like WBC inclusions, giant platelets, thrombocytopenia.
• Non-heme features: nephritis, deafness, cataracts

Question 6

Causes of pseudothrombocytopenia

Answer 6

EDTA effect (plt clumping)
Megathrombocytes
Clotted sample
Abciximab-induced
high protein states ?multiple myeloma
elevated lipids

L: EDTA, platelet satellism, giant platelets

Question 7

Bernard Soulier
Plt size, Plt number, Plt aggregation, Flow cytometry

Answer 7

Bernard Soulier: Deficiency in GP Ib/IX
Plt Size: Large
Plt Number: Low
Platelet aggregation: Absent ristocetin response but normal to every other agonist (GP1b/IX)
Receptor lost: vWF
Flow cytometry: CD42b (expression)

Question 8

Glanzmann Thrombothesenia
Plt size, Plt number, Plt aggregation, Flow cytometry.

Answer 8

Plt Size: normal
Plt Number normal
Platelet aggregation: abnormal to everything except ristocetin (GP2b/3a)
Receptor lost: Fibrinogen
Flow cytometry: CD41/CD61

Question 9

Name 3 infections associated with ITP

Answer 9

H. Pylori
HIV
Hepatitis C
EBV
Intracellular Parasites (malaria, babesia)

Question 10

Glanzmann thrombasthenia, what 2 vaccinations do you need to give

Answer 10

1. Prevnar
2. Pneumococcal
   (can be associated with leucocyte adhesion disease)
   Do not give live vaccines!

Question 11

What is the mechanism of EDTA induced thrombocytopenia?

Answer 11

Results from a “naturally occurring” platelet autoantibody (IgM) directed against a concealed epitope on platelet membrane glycoprotein (GP) IIb/IIIa that becomes exposed by EDTA-induced dissociation of GPIIb/IIIa.

Question 12

What class of proteins is implicated in platelet refractoriness?

Answer 12

Class I HLA (HLA-A and HLA-B are the only clinically significant and typically the only ones tested).
HPA very rare.

Question 13

Causes of macrothrombocytopenia

Answer 13

1. MYH9 disorders
2. ITP
3. BSS
4. Grey Platelet syndrome
5. Montreal plt syndrome
6. X-linked dyserythropoietisis
7. Autosominal dominant thrombocytopenia

Question 14

Treatment of FNAIT

Answer 14

Transfusion of HPA-compatible platelets, which can be collected and washed from the mother or from an antigen-negative donor.

IVIG (1.0 g/kg/d for 1 to 3 days depending on response) and methylprednisolone also may decrease the rate of platelet destruction and can be used as adjunctive therapy.

usually resolves within 2 to 4 weeks spontaneously

Question 15

What percentage of children will experience spontaneous recovery of ITP?

Answer 15

75% of patients achieving a complete remission by 6 months from presentation.

Question 16

Which of the inherited thrombocytopenias can display spontaneous resolution in childhood?

Answer 16

Thrombocytopenia-absent radius syndrome

Question 17

Potential mechanisms of gestational thrombocytopenia?

Answer 17

1. dilutional effect of pregnancy
2. pooling or consumption of platelets in the placenta
3. heightened immunological destruction
4. increased macrophage colony-stimulating factor from the placenta.

Question 18

Woman with gestational thrombocytopenia, plt 70 around time of delivery. Wishes for epidural. What are the Tx options?

Answer 18

On the presumption that there may be a component of immune destruction, a course of low- dose prednisone (10 to 20 mg/day) can be considered in hopes of maintaining the platelet count >80,000/μL to allow for the option of an epidural.

Question 19

What are three approved indications for Eltrombopeg?

Answer 19

1. Severe aplastic anemia
2. Chronic, refractory ITP
3. Chronic hepatitis C to allow the initiation and maintenance of interferon-based therapy (eltrombopag only)

Question 20

TPO, where is it produced. What receptor does it bind to? Are the levels increase or decreased in CAMT? Hereditary thrombocytosis?

Answer 20

1. Produced by the liver [mostly, constitutive] and kidneys
2. It binds to c-MPL (myeloproliferative leukemia virus oncogene)
3. High TPO in CAMT (lack of receptor-mediated uptake), high in HT (gain of function in MPL or TPO)

Question 21

Which pts should be started on Eltrombopag 25mg PO daily as opposed to 50mg PO daily?

Answer 21

1. Patients with moderate to severe hepatic impairment (Child-Pugh score > 7)
2. East Asian ethnicity (higher plasma concentrations than white individuals)

Question 22

What mutation is a/w familial thrombocytopenia and AML?

Answer 22

RUNX1
ANKRD26
ETV6

Question 23

What are two substances in the dense granules of platelets? What are 4 substances in the alpha granules of platelets?

Answer 23

Dense granules- serotonin, ADP/ATP, calcium
(small, need electron microscopy)

Alpha granules-PF4, fibrinogen, FV, vWF, VEGF, P-selectin
(large, can use light microscopy)

Question 24

Is the serum TPO level in ITP low, normal, or high?

Answer 24

Normal! (due to an expanded megakaryocte mass and accelerated platelet clearance)

TPO binds mature platelets [main mechanism of clearance, plt last 7-10d] and megs.

usually low in BMF syndromes
Very high in AA

Question 25

Rituximab in ITP: Time to response, rate of response and average length of response, rate of relapse

Answer 25

1. Average time to response 5.5 wks (R:2-18 weeks) 2. Rate of response ~63% 3. Length of response- 10.5 months 4. Rate of relapse ~25% Long term remission: only 20%

Question 26

What is the mechanism by which ristocetin leads to platelet agglutination in plt aggregation studies?

Answer 26

Ristocetin causes agglutination via vWF binding to GP1b complex. In BSS, there is absence of GP1b-IX and thus agglutination cannot occur. Will also have decreased aggultination with ristocetin in vWD pts (no vWF to bind) but this will normalize with the addition of donor vWF. Ristocetin causes platelet agglutination/adhesion rather than aggregation i.e. there is no binding of fibrinogen.

Question 27

What is Hermansky-Pudlak syndrome?

Answer 27

Rare storage pool disorder AR dz common in Puerto Rico -->characterized by oculocutaneous albinism, a bleeding diathesis, nystagmus and sight issues, pulmonary fibrosis and granulomatous colitis. The bleeding diathesis is caused by the absence of platelet dense bodies.

Question 28

What is Chediak-Higashi syndrome?

Answer 28

Rare storage pool disorder AR dz characterized by δ-SPD, oculocutaneous albinism, immune deficiency, cytotoxic T and natural killer cell dysfunction, neutopenia/neut dyfxn, neurologic symptoms (peripheral neuropathy), and the presence of giant cytoplasmic inclusions in granulocytes (not all cells). Also have mild bleeding phenotype from storage pool defect. - mutations in the lysosomal trafficking regulator (LYST) gene

Question 29

Pts with gray plt disorder have defects in what gene?

Answer 29

NBEAL2 gene

Question 30

What is Montreal plt syndrome?

Answer 30

AD, associated with delayed bleeding and abnormal proteolysis of α-granule proteins resulting from increased amounts of platelet urokinase-type plasminogen activator (uPA). Defective aggregation response with epinephrine. (type 2B VWD with the V1316M VWF mutation). AD, giant platelets, thrombocytopenia, prolonged bleeding time, spontaneous platelet aggregation in vitro.

Question 31

What are 5 causes of acquired storage pool defects in plts?

Answer 31

1. Anti-platelet antibodies 2. SLE 3. Chronic ITP 4. DIC 5. HUS 6. MPN or MDS 7. Leukemia (acute and chronic) 8. Severe valvular disease 9. Patients undergoing cardiopulmonary bypass [activation and loss of granules]

Question 32

Three causes of bleeding in uremia

Answer 32

1. Uremia causing plt dysfunction 2. Plt adhesion defect 3. Storage pool defect 4. Defect in GP IIb/IIIa signaling 5. Decreased plt secretion (ADP, serotonin, TXA2)

Question 33

Pattern of plt aggregation studies in a patient with afibrinogenemia?

Answer 33

Absent to all agonists except ristocetin because ristocetin induced aggregation is independent of fibrinogen! [uses VWF] (so looks like Glanzmann's with all abnormal except Risto)

Question 34

Pattern of plt aggregation studies in a patient on ASA?

Answer 34

Absent aggregation to Arachidonic acid. Primary wave aggregation only with ADP. Decreased or absent aggregation with collagen.

Question 35

Pattern of plt aggregation studies in a patient with Clopidogrel?

Answer 35

Absent aggregation with ADP

Question 36

Pattern of plt aggregation studies in a patient with type2B or plt type vWD?

Answer 36

Pronounced agglutination with low dose Ristocetin e.g. 0.5 mg/mL Positive low dose RIPA Genetic testing fro VWD 2B to tell difference

Question 37

Which of the plt agonists used in plt agg studies are strong vs weak agonists?

Answer 37

Strong Agonists e.g. Collagen, Thrombin, TxA2: These directly induce platelet aggregation, TxA2 synthesis and platelet granule secretion. Weak Agonists e.g. ADP & Epinephrine: These induce platelet aggregation without inducing secretion.

Question 38

What is the pathophys of the primary and secondary wave of ADP binding?

Answer 38

ADP binds to the ADP receptor on the surface of platelets. Initial binding results in the release of intracellular calcium and a change in the shape of the platelet leading to the primary wave of aggregation. The secondary wave reflects the release of ADP from platelet storage granules. Low dose ADP induces only primary aggregation and the effect is reversible.

Question 39

What is Fostamatinib? What disease is it used in?

Answer 39

Spleen tyrosine kinase inhibitor that prevents phagocysosis and immune activation in splenic macrophages -increase the platelet count in patients with ITP by reducing phagocytosis and destruction of autoantibody-coated platelets by macrophages, via inhibition of signal transduction through Fc-activating receptors and the B-cell receptor 100 mg orally twice daily, which can be increased to 150 mg twice daily SE: HTN, liver toxicity

Question 40

Refractory ITP options

Answer 40

Azathioprine CsA MMF Cyclophos Vincristine Danazol Dapsone

Question 41

Issues with Eltrombopag

Answer 41

Take hours away from food Cannot take with calcium containing foods, cations prevent absorption Chelates Iron, worsening iron deficiency Liver enzyme elevations in 10% [respond to holding/decreasing dose] Lower starting dose [25mg daily] if East Asian