Thrombocytopenia as the presenting manifestation of human T-lymphotropic virus type III infection in infants.

Three infants between 8 and 9 months of age developed thrombocytopenia resulting from immune-mediated platelet destruction, as evidenced by the presence of serum antibody to platelets and elevated platelet-associated immunoglobulin G in two patients, and abundant bone marrow megakaryocytes in all patients. The patients had a satisfactory response to corticosteroid therapy, and platelet counts have remained normal during observation after therapy. All patients had serum antibody to human T-lymphotropic virus type III, and HTLV-III was isolated from the peripheral blood lymphocytes in two patients. The HTLV-III infections were presumably acquired via blood transfusions in the neonatal period; none of the patients' mothers belonged to a risk group for HTLV-III infection, and all were HTLV-III seronegative. Although thrombocytopenia was the major clinical manifestation, the patients had a number of immunologic abnormalities characteristic of HTLV-III infection; these included hyperimmunoglobulinemia, a decreased proportion of peripheral blood T cells, and a marked reduction in the proportion of peripheral blood T helper-inducer lymphocytes. We conclude that the patients had immune-mediated thrombocytopenia caused by HTLV-III infection.