Development of Graves' disease during drug-free remission of juvenile dermatomyositis.

We report a Japanese boy with Graves' disease (GD) which developed during drug-free remission of juvenile dermatomyositis (JDM). He had been diagnosed with JDM at the age of 6 years by typical skin rashes, muscle weakness, elevated serum transaminase levels, and typical findings of both magnetic resonance imaging and muscle biopsy. Although anti-melanoma differentiation antigen 5 autoantibody was positive, there was no complication of interstitial lung disease. He showed good response to methylprednisolone pulse therapy followed by oral prednisolone in combination with weekly methotrexate (MTX) and achieved drug-free remission after 3.5 years of treatment. Nevertheless, serum levels of soluble interleukin-2 receptor (sIL-2R) gradually elevated to 3185 U/ml despite no signs of relapse or malignancy. Hyperactivity and attention deficit was also noted. One year and 3 months after the cessation of MTX, he presented with abdominal pain, tachycardia, and apparent goitre. Laboratory tests showed elevated free triiodothyronine, undetectable thyroid stimulating hormone (TSH), and positive anti-TSH receptor antibodies. 99mTc scintigraphy showed high levels of thyroid uptake. He was diagnosed with GD and treated with 15 mg/day of thiamazole. Although transient drug eruption was observed, his thyroid functions are currently well-controlled on 5 mg/day of thiamazole. In conclusion, to our knowledge, this is the first report in English literature describing complication of GD with JDM. Unexpected elevation of sIL-2R could be a clue to the diagnosis of GD during the follow-up of JDM.