Autoantibodies directed against contractile elements of striated muscle are found in 30% adult patients with Myasthenia gravis (MG) and 80% cases of Thymoma in association with MG. The antibodies may also be detected in Lambert - Eaton Myasthenic syndrome (5%), Small cell lung carcinoma (5%), Breast carcinoma, Autoimmune liver disorders and patients on D-penicillamine (25%).