When polymyositis meets Graves' disease: A rare case report

Polymyositis is rarely associated with Graves' disease. A 22- year-old woman was admitted for progressively worsening proximal muscle weakness of both upper and lower extremities. One month prior to admission, she was diagnosed with thyrotoxicosis and prescribed carbimazole 10mg twice daily. Neurological examination confirmed proximal myopathy and blood investigations revealed marked elevation of muscle enzymes, particularly creatine kinase. Electromyography demonstrated myopathic changes while right quadriceps muscle biopsy showed only traces of inflammatory myopathy. She was treated with pulsed intravenous methylprednisolone followed by tapering doses of oral prednisolone, which was eventually down-titrated to 5mg daily during subsequent clinic visits. The initial clinical improvement that she exhibited did not persist despite being rendered euthyroid. She was readmitted approximately one year later with the same complaint. A second course of intravenous methylprednisolone brought about clinical improvement as well as reduction of creatine kinase levels. A diagnosis of polymyositis was then made, for which she was managed with oral prednisolone 20mg daily in combination with gradual up-titration of azathioprine. She continued to show clinical and biochemical improvements during follow-ups. Polymyositis should be considered in the diagnostic workup of proximal myopathy in a patient with Graves' disease, especially in the setting of markedly raised muscle enzymes.