Test for recovery from hypothyroidism during thyroxine therapy in Hashimoto's thyroiditis.

Hypothyroid patients with Hashimoto's thyroiditis usually receive lifelong thyroxine therapy. Some are known to recover thyroid function, but identification of these patients during continued thyroxine therapy has been impossible. 92 patients with hypothyroidism after Hashimoto's thyroiditis and 70 normal controls were studied. All controls but not patient before thyroxine was started had a normal thyroid response to thyroid stimulating hormone (TSH), circulating concentrations of which were increased by administration of 500 micrograms thyrotropin releasing hormone (TRH). During treatment with thyroxine, 22 patients recovered thyroid responsiveness to TSH, and when treatment was stopped these patients have remained euthyroid for 1-8 years, whereas all 70 who did not recover thyroid TSH responsiveness became hypothyroid within 3 months. Over 20% of patients with hypothyroidism after Hashimoto's thyroiditis may recover satisfactory thyroid function, and can be identified during thyroxine treatment by their thyroid response to TSH in a TRH test.