[A case of myasthenia gravis complicated by cyclic thrombocytopenia]

A 47-year-old woman with myasthenia gravis for last 11 years was admitted because of relapsed muscle weakness, hypermenorrhea and thrombocytopenia. Physical and neurological examinations revealed diplopia, proximal muscle weakness and purpuras on the left arm and bilateral legs. Repeated hematological examinations revealed cyclic fluctuation of platelet counts which spontaneously changed from the nadir levels of 12-27 x 10(3)/microliters to the peak levels of 150-400 x 10(3)/microliters. The platelet count reached a nadir at the onset of menstruation. Platelet-associated IgG (PAIgG) was within normal level when platelet count was at an increasing phase. Survival time of autologous platelets was normal when platelet count was at an increasing phase. Megakaryocytes in the bone marrow were apparently normal at the nadir phase. The patient's serum obtained at the nadir of platelet count significantly suppressed megakaryocyte colony forming unit (Meg-CFU) formation in comparison with that after the stabilization of platelet count, suggesting that this cyclic thrombocytopenia was secondary to cyclic hypoproduction of megakaryocytes caused by a suppressive factor. On the other hand muscle weakness showed no cyclic fluctuation. Administration of 60 mg/day prednisolone stabilized the platelet count at about 280 x 10(3)/microliters, abolished hypermenorrhea and gradually improved muscle weakness. These findings suggested autoimmune mechanism in the production of a Meg-CFU-suppressive factor might be involved in the pathogenesis of thrombocytopenia.