A NON-THROMBOCYTOPENIC BLEEDING DISORDER DUE TO AN IGG4-KAPPA ANTI-GPIIB IIIA AUTOANTIBODY/

Autoantibodies in chronic immune thrombocytopenic purpura occasionally interfere with platelet function. We describe a patient with a normal platelet count who had clinically significant mucosal bleeding, a pro longed bleeding time and abnormal platelet aggregation. The patient ha d high titres of an IgG4 kappa autoantibody, directed to a cation-depe ndent epitope on platelet glycoprotein IIb/IIIa, which blocked the bin ding of fibrinogen and fibronectin to this complex. Corticosteroid tre atment resulted in clinical improvement and a marked drop in autoantib ody concentration. The lack of thrombocytopenia in this patient, despi te high autoantibody levels, is best explained by the poor recognition of IgG4 antibodies by phagocytic cells.