KINETIC-STUDIES OF THE MECHANISM OF THROMBOCYTOPENIA IN PATIENTS WITH HUMAN-IMMUNODEFICIENCY-VIRUS INFECTION

Background. Isolated thrombocytopenia accompanied by increased amounts of platelet-associated antibody is a common manifestation of human immunodeficiency virus (HIV) infection, and the thrombocytopenia often improves with zidovudine. It is not clear whether the mechanism of HIV-related thrombocytopenia primarily involves autoimmune destruction of platelets or reduced platelet production by megakaryocytes. Methods. We studied the survival of In-111-labeled autologous platelets and performed platelet imaging in 24 men with isolated HIV-related thrombocytopenia (1 6 who received no treatment and 8 who received zidovudine). We also studied 20 HIV-infected men with normal platelet counts (10 who received no treatment and 10 who received zidovudine) and studied 12 healthy seronegative men as controls. Results. Mean(+/-SD) platelet survival was significantly decreased in both the untreated and the zidovudine-treated patients with HIV-related thrombocytopenia (to 92+/-33 and 129+/-44 hours, respectively; both P<0.001), as compared with the normal controls (198+/-15 hours). Mean platelet survival was also significantly decreased in the HIV-infected patients with normal platelet counts (untreated, 162+/-23 hours, P<0.01; zidovudine-treated, 166+/-35 hours, P<0.05). Imaging studies, however, revealed no evidence of increased clearance of autologous platelets in the liver or spleen in any of these groups. Mean platelet production was significantly depressed in the untreated patients with thrombocytopenia (23,000+/-11,000 platelets per cubic millimeter per day, P<0.001) as compared with the healthy controls (45,000+/-6,000 per cubic millimeter per day). Mean platelet production was significantly increased, however, in the men treated with zidovudine, both in those with thrombocytopenia (60,000+/-31,000 platelets per cubic millimeter per day, P<0.01 vs. controls) and in those without thrombocytopenia (68,000+/-22,000 per cubic millimeter per day, P<0.01). Conclusions. Although there was a moderate reduction in platelet survival in HIV-infected persons, these patients, regardless of platelet counts, also had decreased production of platelets, possibly due to viral infection of the megakaryocytes. Zidovudine appears to improve platelet production.