Arthritis associated with antithyroid therapy in a 15-year-old girl.

A 15-year-old white girl with autoimmune thyroiditis developed arthritis 3 weeks after starting therapy with the antithyroid drug thiamazole. Because an adverse drug reaction of thionamide therapy was suspected, thiamazole was withdrawn, and symptoms disappeared rapidly. Thionamide therapy is indicated for hyperthyroidism and has been widely used since 1948. Reported adverse drug reactions range from mild to potentially life threatening. Arthritis is an uncommon but serious side effect and can develop as a part of the antithyroid arthritis syndrome or as a part of antineutrophil cytoplasmic antibody-associated vasculitis that is induced by antithyroid drugs. Little is known about the exact pathogenesis. Therapy consists of prompt discontinuation of the drug, where upon symptoms rapidly disappear. Because of possible cross-reactivity with alternative thionamides, another form of treatment for hyperthyroidism is recommended. Clinical awareness is important, and prompt withdrawal of the antithyroid drug is necessary when serious side effects occur.