Fixed 30 mCi (1110 MBq) I-131-iodine therapy in autonomously functioning nodules: Single toxic nodule as a predictive factor of success

Aims: The aim of this study is to evaluate the efficacy of a fixed 30 mCi (1110 MBq) I-131-iodine dose for the treatment of hyperthyroidism due to uninodular or multinodular toxic goiter and identify predictors of success. Materials and Methods: Fifty-nine patients diagnosed with nonautoimmune toxic goiter were treated with a fixed 30 mCi dose of I-131-iodine and were followed at a tertiary service between 2000 and 2016. The therapy was considered successful if the patient reached euthyroidism or hypothyroidism without needing an extra I-131-iodine dose or antithyroid drugs for at least 1 year after the radioiodine therapy (RIT). Results: Patients with a single toxic nodule were younger at diagnosis (52 vs. 63 years; P = 0.007), presented a shorter disease duration until RIT (2 vs. 3.5 years; P = 0.007), smaller total thyroid volume (20 vs. 82 cm(3); P = 0.044), and lower pre-RIT thyroid uptake (P = 0.043) than patients with multinodular goiter. No significant difference was seen with antithyroid drug use, thyroid-stimulating hormone and free thyroxine level, and follow-up after RIT. After RIT, 47 patients (79.66%) met the success criteria, and 12 (20.33%) remained hyperthyroid. Among the success group, 32 (68.08%) reached euthyroidism, while 31.92% developed hypothyroidism after 1 year. Patients with single toxic nodules who achieved success after RIT presented smaller nodules (2.8 vs. 5.75 cm; P = 0.043), while the pre-RIT thyroid uptake was higher among patients with multinodular toxic goiter who achieved success after RIT (5.5% vs. 1.5%; P = 0.007). A higher success rate was observed among patients with a single toxic nodule than those with a toxic multinodular goiter (92.3% vs. 55%; P = 0.001), and a single toxic nodule presentation was found to be an independent predictor of success (P = 0.009). Conclusions: The fixed 30 mCi I-131-iodine dose was particularly effective in the group of patients with single autonomously functioning nodule rather than the group with multiple nodules. A single toxic nodule was an independent predictor of treatment success.