Hypothyroidism During Antithyroid Drug Treatment with Methimazole is a Favorable Prognostic Indicator in Patients with Graves' Disease

Background: A major problem with antithyroid drug (ATD) therapy in Graves' disease is the high relapse rate. Therefore, clinicians have sought prognostic indicators of permanent remission. Suppression of serum thyrotropin (TSH) when ATD therapy is stopped carries a poor prognosis, but little is known regarding the significance of elevated serum TSH concentrations in the course of ATD therapy. The objective of this study was to determine if elevated serum TSH concentrations during methimazole (MMI) therapy is associated with a favorable long-term prognosis. Methods: We retrospectively studied patients with Graves' disease who were initially on MMI, in whom this drug was stopped because they had undetectable thyroid-stimulating antibodies (TSAbs) or were euthyroid after at least 24 months on MMI treatment. A strategy of high MMI doses plus T4 was not used in these patients. We identified 40 patients with elevated serum TSH concentration (>10 μIU/mL) during MMI therapy (H-TSH group). Eighty-five percent of t...