Radioiodine therapy in Graves' disease: is it possible to predict outcome before therapy?

OBJECTIVE To assess the predictability of outcome and evaluate the factors that may lead to treatment failure in patients with Graves' disease who are treated with a single dose of radioiodine. MATERIALS AND METHODS This is a retrospective study of 123 patients (M: 42; F: 81) with Graves' disease who received radioiodine therapy with a single fixed (10 mCi) dose for hyperthyroidism. Pretreatment age, sex, BMI, type of anti-thyroid drug used, propylthiouracil doses, iodine uptake, uptake ratio (4/24 h radioiodine uptake), and thyroid volume of the patients in whom radioiodine therapy succeeded or failed were compared. RESULTS Post-therapy follow-up revealed that therapy failed in 22% of the patients. Iodine uptakes and uptake ratios and volumes were found to be significantly higher in patients in whom therapy failed. It was observed that uptake ratio was at least 1 in 25 patients (20%), and therapy failed in 20 (80%) of these patients. Of the 98 patients (80%) in whom uptake ratio was less than 1, therapy was unsuccessful in only seven (7%). CONCLUSION Uptake ratio is a simple index that may be used to predict the patients in whom therapy may fail or succeed. In patients with Graves' disease who have an uptake ratio of less than 1, radioiodine appears to be an effective dose with high success rates. In contrast, because of the high rates of failure in patients with an uptake ratio of at least 1, use of radioiodine therapy at a dose of 10 mCi does not seem to be appropriate.