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Hematology > Platelet disorders > Flashcards

Platelet disorders Flashcards

1
Q

Potential mechanisms of ITP

A
  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. Decreased levels of regulatory T cells activity
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2
Q

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

A

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.

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3
Q

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

A

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

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4
Q

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

A

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)

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5
Q

Name 4 MYH9 disorders

A

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
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6
Q

Causes of psuedothrombocytopenia

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

L: EDTA, platelet satellism, giant platelets

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7
Q

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

A 
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)
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8
Q

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

A 
Plt Size: normal
Plt Number normal
Platelet aggregation: abnormal to everything except ristocetin (GP2b/3a)
Receptor lost: Fibrinogen
Flow cytometry: CD41/CD61
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9
Q

Name 3 infections associated with ITP

A 
H. Pylori
HIV
Hepatitis C
EBV
Intracellular Parasites (malaria, babesia)
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10
Q

Glanzmann thrombasthenia, what 2 vaccinations do you need to give

A
  1. Prevnar
  2. Pneumococcal
    (can be associated with leucocyte adhesion disease)
    Do not give live vaccines!
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11
Q

What is the mechanism of EDTA induced thrombocytopenia?

A

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.

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12
Q

What class of proteins is implicated in platelet refractoriness?

A

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

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13
Q

Causes of macrothrombocytopenia

A
  1. MYH9 disorders
  2. ITP
  3. BSS
  4. Grey Platelet syndrome
  5. Montreal plt syndrome
  6. X-linked dyserythropoietisis
  7. Autosominal dominant thrombocytopenia
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14
Q

Treatment of FNAIT

A

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

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15
Q

What percentage of children will experience spontaneous recovery of ITP?

A

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

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16
Q

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

A

Thrombocytopenia-absent radius syndrome

17
Q

Potential mechanisms of gestational thrombocytopenia?

A
  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.
18
Q

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

A

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.

19
Q

What are three approved indications for Eltrombopeg?

A
  1. Severe aplastic anemia
  2. Chronic, refractory ITP
  3. Chronic hepatitis C to allow the initiation and maintenance of interferon-based therapy (eltrombopag only)
20
Q

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

A
  1. Produced by the liver and kidneys
  2. It binds to 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)
21
Q

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

A
  1. Patients with moderate to severe hepatic impairment (Child-Pugh score > 7)
  2. East Asian ethnicity (higher plasma concentrations than white individuals)
22
Q

What mutation is a/w familial thrombocytopenia and AML?

A

RUNX1
ANKRD26
ETV6

23
Q

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

A

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

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

24
Q

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

A

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

usually low in BMF syndromes

25
Q

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

A
  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%
26
Q

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

A

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 decrease aggultination with ristocetin in vWD pts (no vWF to bind) but this will normalize with the addition of donor vWF.

Ristocetin causes platelet agglutination rather than aggregation i.e. there is no binding of fibrinogen.

27
Q

What is Hermansky-Pudlak syndrome?

A

Rare, AR dz common in Puerto Rica–>characterized by oculocutaneous albinism, a bleeding diathesis, nystagmu and sight issues, pulmonary fibrosis and granulomatous colitis. The bleeding diathesis is caused by the absence of platelet dense bodies.

28
Q

What is Chediak-Higashi syndrome?

A

Rare, 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
29
Q

Pts with gray plt disorder have defects in what gene?

A

NBEAL2 gene

30
Q

What is Montreal plt syndrome?

A

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.

31
Q

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

A
  1. Anti-platelet antibodies
  2. SLE
  3. Chronic ITP
  4. DIC
  5. HUS
  6. MPN
  7. Leukemia (acute and chronic)
  8. Severe vavular disease
  9. Patients undergoing cardiopulmonary bypass
32
Q

Three causes of bleeding in uremia

A
  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)
33
Q

Pattern of plt aggregation studies in a patient with afibrinogenemia?

A

Absent to all agonists except ristocetin because ristocetin induced aggregation is independent of fibrinogen! (so looks like Glanzmann’s)

34
Q

Pattern of plt aggregation studies in a patient on ASA?

A

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

35
Q

Pattern of plt aggregation studies in a patient with Clopidogrel?

A

Absent aggregation with ADP

36
Q

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

A

Pronounced agglutination with low dose Ristocetin e.g. 0.5 mg/mL

37
Q

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

A

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.

38
Q

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

A

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.

39
Q

What is Fostamatinib? What disease is it used in?

A

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

Hematology (20 decks)

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