CYCLIC THROMBOCYTOPENIA ASSOCIATED WITH IGM ANTI-GPIIB-IIIA AUTOANTIBODIES

We studied a female patient with cyclic fluctuation in platelet count following splenectomy for autoimmune thrombocytopenia. The cyclical fl uctuation appeared to be in phase with her menstrual cycle and her pla telet count was low during menses. Bone marrow examinations performed at the peak as well as the bottom of the platelet count showed normal or increased numbers of megakaryocytes. The patient's platelet count i ncreased rapidly after intravenous gamma-globulin (IVIgG) therapy, sug gesting that a failure of platelet production is unlikely to account f or the cycle. Platelet-associated IgM (PAIgM) was markedly elevated, w hereas PAIgG was normal at any stage of the cycle. MACE assay demonstr ated that PAIgM contained IgM anti-glycoprotein (GP) IIb-IIIa autoanti bodies. Comparison between MACE assay using untreated and EDTA-treated platelets at 37 degrees C demonstrated that the platelet-associated I gM autoantibodies mainly recognized divalent cation-dependent conforma tion(s) of GPIIb-IIIa. No antibodies were, however, detected in her se rum. The levels of IgM anti-GPIIb-IIIa showed an inverse relationship with the platelet count. In spite of the marked increase in platelet c ount after IVIgG, however, the levels of IgM anti-GPIIb-IIIa remained elevated. These findings suggest that platelet-associated IgM antiGPII b-IIIa autoantibodies are of pathogenic significance in this patient.