Radioactive iodine in the treatment of Graves' disease

Objectives: This study was performed to evaluate the efficacy of radioactive iodine I'll therapy of Graves' hyperthyroidism at Sultan Qaboos University Hospital, Oman and to determine the optimal dose of I-131 needed to achieve the euthyroid or hypothyroid status. Methods: The medical records of 366 patients with Graves hyperthyroidism who received a single dose of I-131 at Sultan Qaboos University Hospital, Oman between 1991 and 1999 were reviewed. The diagnosis was based on clinical, biochemical grounds and Tc-99m thyroid scintigraphy. The patients were followed up for a minimum period of 12 months. For the analysis, the patients were divided into 6 groups according to the I-131 dose administered: Dose one (350-399), dose 2 (400-449), dose 3 (450-499), dose 4 (500-549), dose 5 (550-599) and dose 6 (greater than or equal to600) MBq. Results: Fifty-eight percent of all the patients were hypothyroid after 3 months. Three hundred and twenty two patients (88%) were treated by a single dose of I-131 in 12 months (85.5% hypothyroid and 2.5% euthyroid). Forty-one patients (11.2%) required a 2nd I-131 dose and only 3 patients required 3 doses of I-131. The best cure rate (93%) was observed in group dose 5 (574.0 +/- 16.4 MBq) which however, was not significantly different from other dosage levels. The female to male ratio was 2:1 and the cure rates were not gender or age related. Conclusion: Treatment of Graves' hyperthyroidism from a single I'll dose is our aim, rather than avoidance of hypothyroidism. Our results indicate that cure rates are higher with larger doses of I-131 except in group dose 6 (special category of patients). In the future, fixed doses would be adopted in our radioactive iodine treatment practice guidelines. As the majority of our patients were hypothyroid at 3 months regular monthly follow-up is essential. Whenever appropriate, physicians are encouraged to consider early referral of Graves' hyperthyroidism patients for radioactive iodine treatment as it is cheap, effective, easy to administer and free from serious side effects.