Giant platelet disorder in a patient with type 2B von Willebrand's disease.

While patients with type 2B von Willebrand's disease often exhibit thrombocytopenia, platelet morphology is typically normal. We describe a 44-year-old Jamaican man with thrombocytopenia and a history of bleeding, who had giant platelets on his peripheral blood film. Functional studies and von Willebrand factor gene sequencing showed him to have type 2B von Willebrand's disease with a heterozygous point mutation resulting in a V553M (V1316M in the new von Willebrand factor gene mutation nomenclature) amino acid substitution. Family studies showed one of his two sisters to have an ill-defined giant-platelet-syndrome with mild thrombocytopenia, but not von Willebrand's disease, indicating that the association of giant platelets and von Willebrand's disease in our patient was most likely coincidental. This report describes the rare concurrence of two uncommon disorders. It also demonstrates how the thrombocytopenia of type 2B von Willebrand's disease can be misdiagnosed as ITP, leading to unnecessary and potentially harmful therapeutic interventions.