[A case of myasthenia gravis following sarcoidosis and rheumatoid arthritis].

We report an elderly woman with sarcoidosis and rheumatoid arthritis who subsequently developed myasthenia gravis. She was given a diagnose of rheumatoid arthritis at the age of 65 years and sarcoidosis, proved by multiple lymphadenopathy with noncaseating granuloma at the age of 67. Prednisolone, methotrexate, and etanercept had been administrated for rheumatoid arthritis. She consulted our hospital because of bilateral ptosis with diurnal fluctuation at the age of 72. Myasthenia gravis was confirmed by an elevated serum anti-acetylcholine receptor antibody titer (1,100 nmol/l, normal <0.2) and a positive edrophonium test. A chest CT showed a small granular structure in the anterior mediastinum, suggesting thymic hyperplasia. This is the first reported case of myasthenia gravis complicated by sarcoidosis and rheumatoid arthritis. Administration of etanercept may be involved in the onset of myasthenia gravis.