Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (394 page)

   Patients with abnormal thromboxane A
₂
synthesis have an aspirin-like defect.

   Impaired release of arachidonic acid.

   Cyclooxygenase deficiency.

   Thromboxane synthase deficiency.

   Disorders of platelet–vessel wall interaction (platelet adhesion defects).

   
Bernard-Soulier
syndrome is an autosomal recessive disorder, caused by absence or abnormalities in the platelet receptor complex GPIb-IX-V. It presents with moderate to severe thrombocytopenia and
giant platelets
. Platelets aggregate normally with ADP, epinephrine, collagen, and arachidonic acid but show delayed aggregation with thrombin and no response to ristocetin (see Table
9-4
).

   
Platelet-type von Willebrand disease
autosomal dominant condition associated with intermittent thrombocytopenia, normal platelet morphology, and decreased levels of high molecular weight vWF multimers. It must be distinguished from von Willebrand disease type 2B.

   Disorders of platelet function related to other defects.

   
Quebec platelet disorder
: excessive fibrinolysis resulting from increased expression and storage of the fibrinolytic enzyme urokinase plasminogen activator in platelets. The defect results in delayed-onset bleeding after trauma or surgery.

   
Scott syndrome
: autosomal recessive disorder due to a defect in platelets’ membrane resulting in inability to assemble prothrombinase and intrinsic tenase complexes.

   The Montreal platelet syndrome was recently documented to be a variant of type 2B von Willebrand disease.

TABLE 9–4. Abnormalities of Platelet Function

ACQUIRED THROMBOCYTOPATHIES