Factors Predicting Treatment Failure in Patients Treated with Iodine-131 for Graves' Disease

Treatment of Graves' disease with iodine-131 (¹³¹I) is well-known; however, all patients do not respond to a single dose of ¹³¹I and may require higher and repeated doses. This study was carried out to identify the factors, which can predict treatment failure to a single dose of ¹³¹I treatment in these patients. Data of 150 patients with Graves' disease treated with 259-370 MBq of ¹³¹I followed-up for at least 1-year were retrospectively analyzed. Logistic regression analysis was used to predict factors which can predict treatment failure, such as age, sex, duration of disease, grade of goiter, duration of treatment with anti-thyroid drugs, mean dosage of anti-thyroid drugs used, ^99mTc-pertechnetate (^99mTcO₄^-) uptake at 20 min, dose of ¹³¹I administered, total triiodothyronine and thyroxine levels. Of the 150 patients, 25 patients required retreatment within 1 year of initial treatment with ¹³¹I. Logistic regression analysis revealed that male sex and ^99mTcO₄^- uptake were associated with treatment failure. On receiver operating characteristic (ROC) curve analysis, area under the curve (AUC) was significant for ^99mTcO₄^- uptake predicting treatment failure (AUC = 0.623; P = 0.039). Optimum cutoff for ^99mTcO₄^- uptake was 17.75 with a sensitivity of 68% and specificity of 66% to predict treatment failure. Patients with >17.75% ^99mTcO₄^- uptake had odds ratio of 3.14 (P = 0.014) for treatment failure and male patients had odds ratio of 1.783 for treatment failure. Our results suggest that male patients and patients with high pre-treatment ^99mTcO₄^- uptake are more likely to require repeated doses of ¹³¹I to achieve complete remission