The Effect of Iodides on Hashimoto's Thyroiditis*

Eighteen patients with Hashimoto's thyroiditis and 4 with a solitary hyperfunctioning thyroidal nodule were given I131 before and after administration of 2000 μg. of stable iodide as potassium iodide. The difference between the 24-hour thyroidal uptakes of the pre-potassium iodide and post-potassium iodide tracers was reduced to a percentage in the manner described by Feinberg and associates. The percentage inhibition of thyroidal I131 uptake in all the cases studied was striking, and differed appreciably from the values for normal persons. It simulated the findings in Graves' disease and iodide goiter. The administration of TSH to normal subjects did not consistently alter the pattern of response to the “iodide inhibition test.” From these preliminary studies it is postulated that iodides enhance a pre-existing intrathyroidal defect that is conceivably related to the organification of iodide.