The major consequence of radioiodine therapy for thyrotoxicosis is hypothyroidism and long-term precise management of hypothyroidism may be problematic. In this study, the long-term outcomes were compared in radioiodine treated euthyroid and hypothyroid patients on thyroid hormone treatment. Materials and Methods: One hundred and thirty eight patients with diffuse toxic goiter were treated with radioactive iodine. One hundred and seven patients (78%) returned for follow up visits for up to 11.5±0.8 years. Numbers of occurrences of thyroid dysfunction in each patient were recorded and a total cost of management was calculated. Results: At the end, 41 patients (38%) were still euthyroid (group 1) and 66 (62%) became hypothyroid (group 2). Serum, FT4, FT3, TSH, thyroid antibodies, lipid profile, calcium, phosphorus, and PTH were measured and bone mineral density, ECG and echocardiography were performed. There was no significant difference in age, sex, duration of symptoms and thyroid function between the 2 groups. The cost of treatment was lower in group 1 than in group 2. During 11.5 years of follow up, percentage of elevated and suppressed TSH in groups 1 and 2 were 0.02 and 20.5, p<0.001 and 7.9 and 13.4, p<0.001, respectively. At the end of 10 years, goiter rate, serum T4, T3, thyroid antibodies, lipids, Ca, P and PTH and bone mineral density and echocardiography data were not signifanctly different between two groups. However, mean serum TSH and number of TSH above 5 mU/L was greater in roup 2 than 1 (p<0.01). Conclusion: It is concluded that thyroid derangements frequently occur in patients who become hypothyroid after radioiodine therapy, while on replacement therapy.
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