Iodine-induced hypothyroidism in euthyroid subjects with a previous episode of subacute thyroiditis.

The effects of the administration of pharmacological quantities of iodide on thyroid function in 18 euthyroid patients with a previous history of painful subacute thyroiditis (SAT) were evaluated, and the results compared to those of iodide administration to 12 euthyroid patients with a previous history of thyroid surgery (TX) for benign nodular thyroid disease. After baseline thyroid function tests, saturated solution of potassium iodide (SSKI; 10 drops; 300 mg iodide) was administered daily for 120 days, and serum T4, T3, and TSH concentrations were assessed 15, 30, 60, 90, 120 days and 2-4 months after SSKI was discontinued. Iodide perchlorate discharge tests were carried out before SSKI administration, and TRH tests were performed on the last day of iodide administration. Two SAT subjects developed clinical evidence of hypothyroidism with markedly elevated serum TSH concentrations, and SSKI was discontinued on days 60 and 90, respectively. Thirteen of 18 SAT patients had at least 1 abnormal thyroid function test (iodide perchlorate discharge test, elevated serum TSH concentration, and abnormal TSH response to TRH) compared to 2 of 12 TX patients. These findings strongly suggest that euthyroid subjects with a previous history of SAT are prone to develop iodide-induced hypothyroidism, suggesting that subtle abnormalities in the thyroid organification of iodide and subsequent thyroid hormone synthesis persist years after the episode of SAT.