Thrombocytopenic purpura with giant platelets and ultrastructural platelet defects

The case of a patient with thrombocytopenia and giant platelets is presented. Platelet function tests including bleeding time, aggregation, availability of PF3, and serotonin uptake and release were abnormal. A bone marrow aspirate showed megakaryocytes that while not increased in number, were young in appearance. Electron microscopy of platelets revealed a dilated surface-connecting canalicular system and a prominent membrane complex. No similar findings were encountered among the patient's relatives. The various diagnostic possibilities in this patient are discussed.