Thiamazole Pretreatment Lowers the 131I Activity Needed to Cure Hyperthyroidism in Patients With Nodular Goiter

Context: Relatively low radioiodine uptake (RAIU) represents a common obstacle for radioiodine (I-131) therapy in patients with multinodular goiter complicated by hyperthyroidism. Objective: To evaluate whether thiamazole (MTZ) pretreatment can increase I-131 therapeutic efficacy. Design and Setting: Twenty-two patients with multinodular goiter, subclinical hyperthyroidism, and RAIU < 50% were randomized to receive either a low-iodine diet (LID; n = 10) or MTZ 30 mg/d (n = 12) for 42 days. Thyroid function and 24-hour RAIU were measured before and after treatment. Thyroid volume was evaluated by either magnetic resonance imaging or single photon emission computed tomography. Results: Mean 24-hour RAIU increased significantly from 32 +/- 10% to 63 +/- 18% in the MTZ group (P < .001). Consequently, there was a 31% decrease in the calculated median therapeutic 131I activity after MTZ (P < .05). No significant changes in 24-hour RAIU were observed after diet. In the MTZ group, median serum TSH levels increased significantly by 9% and mean serum free T-4 and free T-3 concentrations decreased by 22% and 15%, respectively, where as no changes in thyroid function were observed in the LID group. Thyroid volume did not significantly change in either of the two groups. At 12 months after radioiodine treatment, median serum TSH was within the normal range in both groups. Conclusions: MTZ treatment before I-131 therapy resulted in an average 2-fold increase in thyroid RAIU and enhanced the efficiency of radioiodine therapy assessed at 12 months. MTZ pretreatment is therefore a safe, easily accessible alternative to recombinant human TSH stimulation and a more effective option than LID.