A case of polymyositis associated with papillary thyroid cancer: a case report.

Differentiated thyroid cancer is rarely associated with paraneoplastic events. Polymyositis, an autoimmune inflammatory myopathy, can be manifested as a paraneoplastic syndrome (PS). We report a case of a young woman who developed progressive proximal muscle weakness one and a half year after a total thyroidectomy for papillary thyroid cancer. Clinical features, laboratory results and muscle biopsy led us to the diagnosis of polymyositis, possibly related to her previous malignancy. A search for recurrence of the thyroid carcinoma or other underlying malignancy was fruitless. The patient improved slowly but almost completely after about 6 months of immunosupressive therapy, which she is still receiving.