Hashimoto's thyroiditis with clinical manifestations resembling dermatomyositis: a case report.

We report on a 59-year-old man with a 1-year history of forearm erythema, bilateral limb arthralgia, and muscle weakness. During the initial examination we observed infiltrative erythema of the forearm and muscle weakness and atrophy of the limbs. Blood tests revealed marked increases in myogenic enzymes. Because histopathological studies showed lymphocytic infiltration around the small blood vessels in the dermis and mucin deposition, we made a tentative diagnosis of dermatomyositis. However, the specific cutaneous manifestations of dermatomyositis, including heliotrope erythema and Gottron's sign, were absent, and the findings of electromyography were normal. A subsequent detailed examination revealed hypothyroidism and high titers of antithyroglobulin and antimicrosome antibodies, and we made a definitive diagnosis of Hashimoto's thyroiditis. The thyroid function and skin manifestations both improved after treatment with levothyroxine sodium. Dermatomyositis and Hashimoto's thyroiditis can exhibit similar characteristics, and caution is required because of the possibility of misdiagnosis.