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 mu g)-perchlorate discharge test (I-ClO4 test), suggesting a permanent thyroid iodide organification defect. We now re port the results of the I-ClO4 test in patients with hyperthyroid Grav es' 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 Grav es' disease were studied. Before MMI therapy, I-ClO4 tests were carrie d out, and serum T-4, T-3, and TSH were measured to confirm the diagno sis of hyperthyroidism. A positive I-ClO4 test is defined as more than 15% I-131 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 maintai n euthyroidism. Serum T-4, T-3, and TSH were measured monthly. Forty d ays after MMI was discontinued, I-ClO4 tests were repeated, and serum T-4, T-3, and TSH were measured every 2 months thereafter. Before MMI treatment, the I-ClO4 test was positive in 20 of 29 patients (69%) and negative in 9. The favorable responses (normal serum T-4 and T-3 valu es) to MMI therapy were similar in both groups. We have thus far studi ed 16 patients after MMI was discontinued and 9 of 12 patients (75%) w ith a negative I-ClO4 test after MMI therapy, and 1 of 4 patients (25% ) with a positive test remained in remission for a mean of 7 months.