Effect of long-term continuous methimazole treatment of hyperthyroidism: comparison with radioiodine

Objective: To investigate the long-term effects of continuous methimazole (MMI) therapy. Design and methods: Five hundred and four patients over 40 years of age with diffuse toxic goiter were treated with MMI for 18 months. Within one year after discontinuation of MMI, hyperthyroidism recurred in 104 patients. They were randomized into 2 groups for continuous antithyroid and radioiodine treatment. Numbers of occurrences of thyroid dysfunction and total costs of management were assessed during 10 years of follow-up. At the end of the study, 26 patients were still on continuous MMI (group 1), and of 41 radioiodine-treated patients (group 2), 16 were euthyroid and 25 became hypothyroid. Serum thyroid and lipid profiles, bone mineral density, and echocardiography data were obtained. Results: There was no significant difference in age, sex, duration of symptoms and thyroid function between the two groups. No serious complications occurred in any of the patients. The cost of treatment was lower in group 1 than in group 2. At the end of 10 years, goiter rate was greater and antithyroperoxidase antibody concentration was higher in group 1 than in group 2. Serum cholesterol and low density lipoprotein-cholesterol concentrations were increased in group 2 as compared with group 1; relative risks were 1.8 (1.12-2.95, P < 0.02) and 1.6 (1.09-2.34, P < 0.02) respectively. Bone mineral density and echocardiographic measurements were not different between the two groups. Conclusion: Long-term continuous treatment of hyperthyroidism with MMI is safe. The complications and the expense of the treatment do not exceed those of radioactive iodine therapy.