Serial studies were performed in two patients with
cyclic thrombocytopenia to investigate the pathogenesis of this disorder. Mean life span of autologous platelets when platelet levels were declining was subnormal (2.4 and 0.8 days), and megakaryocytes were abundant in the bone marrow during
thrombocytopenia. Megakaryocyte colony-stimulating activity could not be detected in the serum of either patient at any point of their cycles. In each patient, total platelet-associated
IgG varied inversely with platelet levels. Surface platelet-associated
IgG was measured only in patient 2 and was significantly elevated (greater than 1,280
IgG molecules per platelet) at all stages of the cycle, even during
thrombocytosis. However, the highest values were observed during
thrombocytopenia. Platelet-bindable
IgG in plasma declined to normal immediately before platelet levels began to rise.
IgG eluted from the platelets of this patient reacted strongly with autologous and homologous platelets in contrast to a "mock eluate" prepared from platelets of a normal subject. The eluate from the patient's platelets reacted strongly with immobilized autologous and homologous
glycoprotein IIb/IIIa complex and weakly with GPIb but not with isolated
GPIIIa alone. In each patient the decline in platelet levels was significantly delayed following administration of intravenous
gamma globulin 0.4 g/kg
body weight for five days. These findings suggest that platelet-reactive
autoantibodies are of pathogenic significance in some patients with
cyclic thrombocytopenia.