Myasthenia gravis: difference between thymoma-associated antibodies and cross-striational skeletal muscle antibodies

Serum from 20 of 137 patients (15%) with myasthenia gravis (MG) contained antibodies to a citric acid extract (CAE) of skeletal muscle. A thymoma was found in all 19 of these patients who were thymectomized. There was no evidence of thymoma in patients who did not have CAE antibodies. Serum from 40 of the same 137 patients (30%) contained antibodies that gave a cross-striational immunofluorescent pattern in skeletal muscle. This pattern was seen with serum from 16 of the 20 thymoma patients, but also with serum from 24 patients without thymoma. The cross-striation antibodies were not absorbed by CAE coated on to tanned sheep erythrocytes. Accordingly, antibodies detected in the two tests have different specificities.