Radioactive iodine in the treatment of Graves' disease

OBJECTIVE: This study was performed to evaluate the efficacy of radioactive iodine 131I therapy of Graves' hyperthyroidism at Sultan Qaboos University Hospital, Oman and to determine the optimal dose of 131I needed to achieve the euthyroid or hypothyroid status.

METHODS: The medical records of 366 patients with Graves hyperthyroidism who received a single dose of 131I at Sultan Qaboos University Hospital, Oman between 1991 and 1999 were reviewed. The diagnosis was based on clinical, biochemical grounds and 99mTc 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 131I 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 (>=600) 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 131I in 12 months (85.5% hypothyroid and 2.5% euthyroid). Forty-one patients (11.2%) required a 2nd 131I dose and only 3 patients required 3 doses of 131I. 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 131I dose is our aim, rather than avoidance of hypothyroidism. Our results indicate that cure rates are higher with larger doses of 131I 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.