The iodine perchlorate discharge test before and after one year of methimazole treatment of hyperthyroid Graves' disease

We have recently reported that many euthyroid patients with a history of Graves' disease treated years earlier with methimazole (MMI) have a positive iodide (500 micrograms)-perchlorate discharge test (I-ClO4 test), suggesting a permanent thyroid iodide organification defect. We now report the results of the I-ClO4 test in patients with hyperthyroid Graves' disease before beginning a 1-yr course of MMI therapy and 40 days after MMI was discontinued. Twenty-nine patients (25 women and 4 men; mean age, 38 +/- 1.7 yr) with their first episode of hyperthyroid Graves' disease were studied. Before MMI therapy, I-ClO4 tests were carried out, and serum T4, T3, and TSH were measured to confirm the diagnosis of hyperthyroidism. A positive I-ClO4 test is defined as more than 15% 131I discharged from the thyroid 1 h after the administration of 1 g KClO4. Patients were then treated with 20 mg MMI for the first 2 months and variable doses thereafter for the next 10 months to maintain euthyroidism. Serum T4, T3, and TSH...