[Association of polymyositis, myasthenia, and thymoma. A case and review of the literature].

We report the case of a 51 years old woman with myositis, myasthenia gravis and thymoma. First apparent sign is myositis in 1976 but chest X ray show a mediastinal opacity and the patient reports an intermittent diplopia since 1973. The evolution of myositis occurs in two bouts in 1976 and 1981, Myasthenia gravis restricted to diplopia from 1973 to 1979 grow worse first alone then in association with increase of myositis signs in 1981. The mediastinal opacity seen on chest X ray in 1976 don't change and is revealed to be a thymoma at operation in 1981. After thymoma ablation myasthenic and myositis signs decrease. This pathologic association is found 24 times in literature and involves "giant cells" in muscle biopsy in about 50 p. 100 of cases and a myocarditis also with "giant cells". Those "giant cells" unusual in common myositis appears to have a prognostic value.