Platelets

Question 1

Glanzmann’s thrombasthenia

Answer 1

absence of the platelet Gp IIb/IIIa receptor

Glanzmann’s thrombasthenia (absence of the platelet Gp IIb/IIIa receptor) and Bernard- Soulier syndrome (absence of the platelet Gp Ib-IX-V receptor).

Both are inherited in an autosomal recessive fashion and present with bleeding symptoms in childhood.

Question 2

Bernard- Soulier syndrome

Answer 2

absence of the platelet Gp Ib-IX-V receptor

Glanzmann’s thrombasthenia (absence of the platelet Gp IIb/IIIa receptor) and Bernard- Soulier syndrome (absence of the platelet Gp Ib-IX-V receptor). Both are inherited in an autosomal recessive fashion and present with bleeding symptoms in childhood.

Question 3

Platelet storage pool disorder (SPD)

1. what is it?
2. inheritance pattern
3. what causes it
4. how it appears

Answer 3

Platelet storage pool disorder (SPD): a “secretion defect”

1. the classic autosomal dominant qualitative platelet disorder.
2. abnormalities of platelet granule formation.
3. It is also seen as a part of inherited disorders of granule formation, such as Hermansky-Pudlak syndrome.
4. Bleeding symptoms in SPD variable but often mild.

The most common inherited disorders of platelet function prevent normal secretion of granule content and are termed secretion defects. Few of these abnormalities have been dissected at the molecular level but they likely result from various mutations.

Question 4

Hermansky-Pudlak syndrome

Answer 4

latelet storage pool disorder (SPD) is the classic autosomal dominant qualitative platelet disorder. This results from abnormalities of platelet granule formation. It is also seen as a part of inherited disorders of granule formation such as Hermansky-Pudlak syndrome.

Bleeding symptoms in SPD are variable, but often are mild. The most common inherited disorders of platelet function prevent normal secretion of granule content and are termed secretion defects. Few of these abnormalities have been dissected at the molecular level but they likely result from various mutations.

Question 5

Platelet disorders associated with milder bleeding symptoms frequently respond to

Answer 5

desmopressin

Question 6

DDAVP

Answer 6

DDAVP increases plasma VWF and factor VIII levels

it may also have a direct effect on platelet function

Particularly for mucosal bleeding symptoms, antifibrinolytic therapy (ε- aminocaproic acid or tranexamic acid) is used alone or in conjunction with DDAVP or platelet therapy.

Question 7

DDAVP

Answer 7

1. DDAVP increases plasma VWF and factor VIII levels
2. it may also have a direct effect on platelet function.
3. Particularly for mucosal bleeding symptoms–> antifibrinolytic therapy (ε- aminocaproic acid or tranexamic acid) is used alone or in conjunction with DDAVP or platelet therapy.

Question 8

DDAVP might be used with what else?

Answer 8

antifibrinolytic therapy (ε- aminocaproic acid or tranexamic acid) is used alone or in conjunction with DDAVP or platelet therapy.

Question 9

Acquired platelet dysfunction is usually due to

Acquired platelet dysfunction occurs in ____

Answer 9

Acquired platelet dysfunction is usually due to medications

1. intentionally: as with antiplatelet therapy
2. unintentionally: as with high-dose penicillins.

Acquired platelet dysfunction occurs in uremia.

Question 10

how do we treat platelet defects arising from uremia?

Answer 10

Acquired platelet dysfunction occurs in uremia. This is likely multifactorial, but the resultant effect is defective adhesion and activation. The platelet defect is improved most by dialysis but may also be improved by

1. increasing the hematocrit to 27–32%
2. giving DDAVP (0.3 μg/kg)
3. use of conjugated estrogens.

Platelet dysfunction also occurs with cardiopulmonary bypass due to the effect of the artificial circuit on platelets, and bleeding symptoms respond to platelet transfusion.

Question 12

Glanzmann Thrombasthenia: Ristocetin

Answer 12

Glanzmann Thrombasthenia:

1. (+) Ristocetin (positive aggregation)
2. No aggregation to everything else

Question 13

Bernard Soulier Syndrome: Ristocetin test

Answer 13

Bernard Soulier Syndrome (-)

1. Ristocetin (absent aggregation)
2. Normal to everything else (ADP, collagen, arachidonic acid, epinephrine)

Question 14

vW disease: ristocetin test

Answer 14

vW disease:

1. (-) Ristocetin (absent aggregation)
2. Tx: Cryoprecipitate - replaces vWF
3. DDAVP (Desmopressin) → causes release of vWF from endothelium