Previous studies have demonstrated association of acquired RMD with autoimmune disorders, or less commonly with cancer. AChR antibodies are often observed in RMD in parallel with the presumed immune-mediated etiology of acquired RMD. Despite having AChR antibodies, acquired RMD patients may exhibit minimal or no manifestations of myasthenia gravis (MG). Treatment selection in these RMD patients may prove challenging.

Three patients with acquired RMD were identified. These were men with classic RMD symptoms beginning in the fourth to sixth decade. Two developed ocular MG after onset of RMD, while the third had no MG symptoms. None had other autoimmune disorders or malignancy. AChR-binding antibodies were detected in all three patients, and two had positive striational antibodies. None had thymoma. Creatine kinase was mildly elevated, and caveolin-3 genetic testing was negative in all three patients. Concentric needle electromyography showed electrical silence during spontaneous muscle contractions in 2 of 3 patients. The third patient exhibited decreased caveolin-3 and dystrophin sarcolemmal immunoreactivity on muscle biopsy. All patients received at least one immunosuppressive (IS) therapy. While MG symptoms responded to IS treatment, RMD symptoms were more refractory. Only one individual who received intravenous immunoglobulin (IVIg) experienced significant improvement in RMD symptoms. Symptomatic treatment for RMD yielded only minimal benefit.