A case of polymyositis associated with chronic thyroiditis presenting as hyperthyroidism

We describe a case of polymyositis associated with hyperthyroidism (Graves' disease). Clinical findings and thyroid function tests revealed hyperthyroidism. On histological examination, it was found that the thyroid gland was involved in chronic thyroiditis, and no appearance of Graves' disease was noted. This case suggested that the patient's muscle weakness might have been related to a disturbance of thyroid function, that is, coexistence of subclinical thyrotoxic myopathy. There were fluctuations in the levels of various antibodies during the clinical course of this overlap syndrome.