We report the case of a 42-year-old male patient with acute onset of asymmetrical polyarthritis of the medium and large joints as well as fever and elevated serological inflammation markers. The symptoms began shortly after initiation of thiamazole treatment for newly diagnosed Graves' disease. Antithyroid arthritis syndrome (AAS) is a rare but serious adverse side effect of antithyroid treatment with thioamides such as thiamazole. Clinically, AAS may present with myalgia, arthralgia, fever, exanthema and polyarthritis. In the case of suspected AAS, when possible the thionamide medication should be rapidly discontinued or modified in consultation with the endocrinologist. In some cases anti-inflammatory therapy with NSAID or corticosteroids may be required for symptom control.
