Coronary thrombosis in a patient with May-Hegglin anomaly.

May-Hegglin anomaly (MHA) is a rare hereditary condition that is characterized by cytoplasmic inclusions in leukocytes and giant platelets. Many patients have some degree of thrombocytopenia. Most individuals with MHA are asymptomatic, but 25-43% of patients previously reported have had a hemorrhagic tendency. The authors describe a patient with MHA who had no history of hemorrhage but who developed complete coronary thrombosis after attempted angioplasty despite an apparent platelet count of 24,000 per mm3. Laboratory investigations revealed a normal bleeding time, normal platelet aggregation, and an increase in the size of approximately two-thirds of the platelets. The calculated platelet mass was near normal, which probably explains the thrombosis despite a decrease in platelet numbers. The authors conclude that in some patients with MHA platelets are functionally active both in vivo and in vitro.