Autoimmune thrombocytopenia in sarcoidosis.

Severe thrombocytopenia and splenomegaly developed in a young man with sarcoidosis. Platelet-associated immunoglobulin (IgG) was strongly positive, and platelet survival studies revealed a half-life of five and a half hours. Treatment with prednisone and vincristine led to a rise in the platelet count to 100,000/mm3 after two months with no change in the splenomegaly. Five months later, when the platelet count was normal, the level of platelet-associated IgG had fallen to normal. Repeated platelet survival studies showed an initial half-life of three hours with a second half-life of two days, associated with accumulation in the spleen. Although there was evidence for splenic sequestration of platelets, the dominant mechanism of thrombocytopenia appeared to be antibody-mediated destruction, analogous to that seen in idiopathic autoimmune thrombocytopenic purpura and responsive to immunosuppressive therapy.