hematology and oncology
Hereditary Intrinsic Platelet Disorders
Disorders of platelet activation
Disorders of amplification of platelet activation are the most common hereditary intrinsic platelet disorders and produce mild bleeding. They may result from decreased ADP in the platelet granules (storage pool deficiency), from an inability to generate thromboxane A2 from arachidonic acid, or from an inability of platelets to aggregate in response to thromboxane A2. Platelet aggregation tests reveal impaired aggregation after exposure to collagen,epinephrine, and low levels of ADP and normal aggregation after exposure to ristocetin and high levels ofadenosinediphosphate (ADP). The same pattern can result from use of nonsteroidal anti-inflammatory drugs (NSAIDs) oraspirin, the effect of which can persist for several days. Therefore, platelet aggregation tests should not be done in patients who have recently taken these drugs. Thrombasthenia(Glanzmann disease) is a rare autosomal recessive disorder causing a defect in the platelet glycoprotein IIb/IIIa receptor; platelets cannot aggregate. Patients may have severe mucosal bleeding (eg, nosebleeds that stop only after nasal packing and transfusions of platelet concentrates). The diagnosis is confirmed by the finding that platelets fail to aggregate after exposure toepinephrine, collagen, or even high levels of ADP but do aggregate transiently after exposure to ristocetin. Platelet transfusion is necessary to control serious bleeding. 