Efficacy of radioiodine in the treatment of primary hyperthyroidism

Abstract

Background: Radioiodine (RI) is a commonly used treatment modality for primary hyperthyroidism. A single dose of RI has been reported to cure hyperthyroidism in the range of 50%–90% of the treated cases. The efficacy of RI treatment has not yet been investigated in the local population. Objectives: To assess the efficacy of RI therapy in patients with primary hyperthyroidism treated at Tawam Hospital, Al Ain, UAE. Patients and Methods: The electronic medical records of hyperthyroid patients who received RI treatment at Tawam Hospital between January 2009 and March 2017 were reviewed. The diagnosis was verified by reviewing clinical, laboratory, and imaging data. Following RI therapy, a cure was defined as the development of hypothyroidism or euthyroid status without the aid of antithyroid drugs (ATDs) within 6 months post-RI therapy. Multivariate analysis was used to assess predictors of RI response. Results: A total of 125 patients (68.8% women) met the study criteria. The mean age ± standard deviation (SD) at RI therapy was 40 ± 15.1 years. The etiology of hyperthyroidism was available for 121 patients; Graves' disease (GD) (n = 83, 68.6%), toxic multinodular goiter (TMNG) (n = 31, 25.6%), and toxic adenoma (TA) (n = 7, 5.8%). The majority of patients (109, 87.2%) were pretreated with ATDs; 70.3% of those were treated for a period exceeding 18 months. Almost quarter of the patients were referred to RI due to other compelling medical reasons including ATDs intolerance, neutropenia, and hepatotoxicity. The mean ± SD administered RI activity was 14.6 ± 3.7 mCi (range: 8–25). Treatment response evaluation was possible in 97 cases. Post a single dose of RI treatment, 91.8% of patients achieved either euthyroid or hypothyroid status. Patients with GD developed hypothyroidism more frequently than TMNG or TA (80.6% vs. 65.2% vs. 33.3%, respectively). The time to cure was within 3 months in 21% and 3–6 months in 79% of the patients. The given dosage of I131 was the only predictor of cure rate. No major adverse effects were reported. Conclusion: We found that there is a delay in referring potential patients with hyperthyroidism for RI treatment and the cure rate of a single dose of I131 is 91.8% within 6 months of posttreatment; patients with TA may require higher doses of I131 therapy. Further studies are needed to explore the patient–physician barriers in utilizing RI as a timely mode of treatment for appropriately selected patients.