[Still's disease in adults and polymyositis. An infrequent association]

A case of coexistence of adult onset Still's disease and idiopathic inflammatory myopathy is reported in a patient with antecedent of Graves-Basedow disease. Although myalgias are common during the flares of adult onset Still's disease, a review of literature only disclosed two previous cases of polymyositis associated to adult onset Still's disease. A high index of suspicion is needed in order to diagnose such a rare association which has relevant prognostic and therapeutic implications. Treatment with methotrexate was started in order to control myopathy, resulting in improvement of both polymyositis and adult onset Still disease. A possible role of methotrexate in the management of adult onset Still's disease is suggested.