Background: There is no general agreement as to which treatment is best for hyperthyroidism. The objective of this study is to investigate the effectiveness of continuous methimazole (MMI) treatment and to compare the results of neuropsychological testing in patients receiving long-term continuous MMI to those on replacement thyroxine following radioiodine-induced (RAI) hypothyroidism.
Methods: We enrolled 239 patients with diffuse toxic goiter who had recurrences of hyperthyroidism. Of these, 104 patients were randomized into two groups, MMI and treatment with thyroxine following RAI hypothyroidism. The remaining 135 patients voluntarily enrolled into either of the two groups. From all patients, 59 MMI-treated patients and 73 patients in the RAI group completed follow up. Thyroid function tests, serum lipids and lipoproteins, echocardiography, bone mineral density (BMD) and seven neuropsychology tests were performed at the final visit.
Results: In the RAI group compared to the MMI-treated group during a mean of 14 years follow up, there were more incidences of elevated TSH [> 5 mU/L; adjusted relative risk (RR) 1.23; 95% confidence interval (CI) 1.04-1.47), increased triglycerides (> 150 mg/dL; RR 2.20; 95% CI 1.34-3.62), HDL-C (< 40 mg/dL; RR 3.46; 95% CI 1.40 - 8.53), and early diastolic annular velocity (< 12.2 cm; RR 3.91; 95% CI 1.42-10.74), in addition to a decreased early diastolic to annular velocity ratio (< 6.7; RR 7.14; 95% CI 1.38-34.48). The MMI group scored better in neuropsychology tests that included mood, direction, logical memory, repeated numbers, and intelligence quotient (IQ).
Conclusion: Long-term MMI treatment was superior to RAI therapy in patients with diffuse toxic goiter when mood, cognition, cardiac function and occurrence of thyroid dysfunction were compared.
Trial registration: Iranian Registry of Clinical Trials: IRCT 201009224794N1.