Inflammatory myopathy in thyrotoxicosis.

A 45-year-old man with a 3-month history of episodic muscle weakness, MRC grade 4/5 symmetric hip flexor weakness, elevated CK, and an inflammatory myopathy was found to have elevated free thyroxine and T3. Treatment with carbimazole resulted in complete resolution of symptoms and return of muscle power to normal. A repeat biopsy revealed resolution of the inflammatory endomysial infiltrate and an absence of necrosis. Complete clinical and pathologic resolution of a thyrotoxicosis-associated inflammatory myopathy without steroid therapy has not been previously described. The favorable outcome experienced by this patient indicates that steroids may not be necessary in thyrotoxicosis-associated inflammatory myopathy.