Sustained Control of Graves' Hyperthyroidism During Long-Term Low-Dose Antithyroid Drug Therapy of Patients with Severe Graves' Orbitopathy

Background: Patients with severe Graves' orbitopathy often have hyperthyroidism that is difficult to treat and a high proportion of patients experience relapse of hyperthyroidism after a course of antithyroid drug (ATD) therapy of fixed duration. The aim of the study was to evaluate the feasibility of prolonged low-dose ATD therapy for attaining stable euthyroidism in patients with severe Graves' orbitopathy and hyperthyroidism. Methods: We performed retrospective analyses of data collected during observation of a cohort of patients (n = 108) treated for severe Graves' orbitopathy and for hyperthyroidism using partial block with low-dose thionamide + replacement with levothyroxine (L-T4) for >2 years. The study was performed at a university hospital referral center for patients with severe Graves' orbitopathy. Results: The median duration of thionamide therapy was 80 months (25-75 percentiles: 55-115 months); 101 patients received methimazole (median: 5 mg/day) without side effects during prolonged therapy, and 7 propylthiouracil (median: 200 mg/day); median L-T4 dose was 0.1 mg/day. Ninety percent of patients remained euthyroid throughout the period of therapy, and 65% of them had thyroid stimulating hormone (TSH) receptor antibodies in serum within the assay reference interval at the last observation. Only four (3.7%) developed episodes of hyperthyroidism during stable therapy, and 94% had serum TSH within 0.1-4.0 mU/L at the last observation. One patient developed reversible cutaneous vasculitis after 6 years of propylthiouracil therapy. Conclusions: Prolonged partial block plus replacement therapy with low-dose ATD + L-T4 keeps the majority of patients with severe Graves' orbitopathy and hyperthyroidism stable and euthyroid.