Abstract

Polymyositis (PM), an autoimmune inflammatory myopathy, can be manifested as a paraneoplastic syndrome (PS). Reports on the association of PM with thyroid cancer are very few. This report presents the case of a 69-year-old woman who had a history of autoimmune hypothyroidism, treated with thyroxin. She developed progressive proximal muscle weakness. Clinical features, laboratory results and muscle biopsy led us to the diagnosis of polymyositis. Few days later, after corticoid therapy, she showed the symptoms of a thyroid carcinoma, most likely anaplastic. Although the association between malignancy and polymyositis remains controversial, to our knowledge this is the first report of anaplastic thyroid carcinoma (ATC) occurring in association with polymyositis and auto-immune hypothyroidism. As a result, thyroid studies should be performed in cancer investigations in PM cases.