[A case of polymyositis in autoimmune thyroiditis with hyperthyroidism].

A young woman, during an autoimmune thyroiditis with hyperthyroidism, suffered from progressive proximal weakness at her four limbs. The diagnosis of a concomitant polymyositis was indicated by a marked increase of plasma CPK, myopathic findings at EMG and a clearcut picture of inflammatory alterations at muscle biopsy. Steroid therapy brought a full recovery of both thyroid and muscular symptoms. In the following months, the patient suffered from a second episode of thyroiditis and subsequently from another poussée of polymyositis. The possible pathogenesis underlying the unusual association of an autoimmune thyroiditis with a polymyositis is discussed.