Clinical characteristics and prognosis of myasthenia gravis with other autoimmune diseases.

Of 277 patients with myasthenia gravis (MG) who underwent thymectomy, including 78 with thymomatous MG, 33 patients had other autoimmune diseases. The clinical characteristics of MG with other autoimmune disease were investigated. Graves's disease and rheumatoid arthritis were the most common autoimmune diseases seen. The association rate of autoimmune disease in patients with thymomatous MG (3.8%) was significantly lower than that in patients with nonthymomatous MG (15.1%). The positive rate for a germinal center in the thymus was significantly higher in patients with other autoimmune disease than in those without such disease. Thymectomy was effective for MG in patients with an associated disease as well as in those without such a complication. The clinical course of the associated autoimmune disease did not seem to be adversely affected by thymectomy. Therefore, thymectomy should be performed in MG patients with other autoimmune disease.