Heart muscle antibodies in myasthenia gravis.

Myasthenia gravis (MG) may in some patients, especially in those with a thymoma, involve the heart. Using an ELISA, we measured heart muscle antibodies in sera from 75 MG patients and in 173 control sera. Heart muscle antibodies were detected in 29/30 thymoma MG patients, in none of 30 young onset MG patients with thymic hyperplasia and in 7/15 late onset MG patients with thymic atrophy. Among the controls, four sera had a very low concentration of heart muscle antibodies. Absorption studies showed that the heart muscle antibodies cross-react with skeletal muscle, but are unrelated to acetylcholine receptor antibodies.