Influence of therapeutic inorganic iodine on long-term prognosis of Graves' disease: a multicenter prospective observational study.

Abstract

Inorganic iodine has long been used as a treatment for Graves' disease. It is currently a treatment option for mild Graves' disease, but there have been no data suggesting the validity of continuing low-dose iodine treatment after improvement in thyrotoxicosis. For this prospective observational study, we recruited patients with Graves' disease treated only with low-dose iodine (potassium iodine ≤25 mg/day). These patients were then divided into two groups: those who continued with low-dose iodine (C group) and those who discontinued it (DC) group. We compared the 2-year thyrotoxicosis relapse rate between the two groups and investigated anthropometric variables associated with relapse. Of 2,159 patients on iodine treatment, 56 patients met the selection criteria but 4 who gave consent dropped out, leaving 25 in the C group and 27 in the DC group. Regarding baseline characteristics, the C group had a longer duration of Graves' disease, lower therapeutic iodine doses, and lower TSH levels than the DC group. During the 2-year follow-up period, the relapse rate in the C and DC groups was 32.0% and 22.2%, respectively (p = 0.536). Furthermore, patients who relapsed had significantly higher therapeutic iodine doses, FT4 levels, and TSAb levels at baseline than patients who did not relapse. Multiple logistic regression showed that relapse is positively associated with therapeutic iodine dose and TSAb levels. The present study failed to show the efficacy of continuing low-dose iodine in patients with Graves' disease after improvement in thyrotoxicosis. The relapse rate seems to be affected by residual immune activity. UMIN000047660.