Serum antibodies to cytomegalovirus in myasthenia gravis: effects of thymectomy and steroids.

The etiology of the immunologic abnormalities in myasthenia gravis (MG) remains unknown. Evidence for persistent viral infection was sought by determining serum antibody titers to several enveloped RNA and DNA viruses. Compared to healthy controls matched for age, sex, geography and socioeconomic status, patients with MG were more likely to have elevated titers of complement-fixing antibody to cytomegalovirus (CMV). Patients with MG not treated with thymectomy or steroids had elevated CMV titers, whereas thymectomized or steroid-treated patients did not; the differences were statistically significant (p less than 0.01). These results are consistent with the hypothesis that there is persistent viral antigenic stimulation in the myasthenic thymus, arising from viral protein incorporation into epithelioid-myoid cell surface membranes and subsequent induction of an antibody to these acetylcholine receptor (AChR)-bearing thymic cells. This antibody then cross-reacts with AChR at the neuromuscular junction.