Giant platelets in hereditary macrothrombocytopenia

Peripheral blood smear shows many giant platelets (arrows) in a young woman with congenital thrombocytopenia. The patient has persistent severe thrombocytopenia and high-frequency sensorineural hearing loss, a constellation of findings consistent with one of the congenital macrothrombocytopenias. The patient had been erroneously diagnosed as having immune thrombocytopenia (ITP) during childhood and had been treated with glucocorticoids and splenectomy with no response.

High-power view of a normal peripheral blood smear. Several platelets (arrowheads) and a normal lymphocyte (arrow) can also be seen. The red cells are of relatively uniform size and shape. The diameter of the normal red cell should approximate that of the nucleus of the small lymphocyte; central pallor (dashed arrow) should equal one-third of its diameter.