Document Type: Original Article
Endocrinology and Metabolism Research Center, Tehran University of Medical Sciences, Tehran, Iran
Research Institute for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Introduction: Radioiodine (131I) is an effective and inexpensive alternative to surgery in the treatment of thyroid hyperfunction. The debate today concerns the maximum and minimum ablative doses, and factors leading to hypothyroidism. Patients & Method: 1035 hyperthyroid patients treated with weight-adjusted ablative doses of 131I were retrospectively assessed for treatment outcome or correlated with sex, age, underlying pathology, and administrated dose of 131I. Results: Thyroid hyperfunction was 3.5 times more common in women. The greatest proportions of patients were in the 31-40 years age group and the smallest proportion over-70. The commonest underlying pathology was Grave’s disease. Men had a lower response rate to 131I therapy, with 2.4-fold greater probability of persistent hyperthyroidism (P<0.0001). The probability of post-131I hypothyroidism decreased with increasing age (P<0.0001). The best response to 131I therapy was seen in patients with toxic adenoma, (P=0.0001). The incidence of hypothyroidism did not show a positive correction with increased administered dose of 131I (P<0.001). Average time to develop clinical hypothyroidism was 7.1 months. 131I was effective in reducing thyroid nodule size. There were 18 cases of temporary hypothyroidism, all of which recovered to euthyroid status within 12 months. Conclusion: One dose of radioiodine was effective in treatment of hyperthyroid patients in 91.2% of cases. Age, sex and underlying pathology were determining factors. In most cases the average time to hypothyroidism was reasonably short, obviating the need for long time follow up in these patients.