SPONTANEOUS HYPOTHYROIDISM IN SYMPTOMLESS AUTOIMMUNE THYROIDITIS. A LONG‐TERM FOLLOW‐UP STUDY

Abstract

A follow-up study was performed on subjects with symptomless autoimmune thyroiditis to obtain information on the natural course of the disease. Seven out of the 22 subjects with symptomless autoimmune thyroiditis became hypothyroid within 4-48 mo. of observation, whereas 15 subjects were still euthyroid after an observation period of 26-102 mo. The yearly incidence of hypothyroidism in symptomless autoimmune thyroiditis was 7.3%. The basal serum TSH level and the response of serum TSH to TRH was initially elevated in all subjects who developed hypothyroidism. The annual incidence of hypothyroidism was 26% in the subjects with an initially elevated TSH level. Serum TSH was initially normal in all but 1 of the 11 subjects with symptomless autoimmune thyroiditis in whom it was measured, and who remained euthyroid. In this group the TRH response was initially slightly exaggerated in 3 out of 10 subjects. It was not performed in 5 subjects. During the follow-up, serum TSH and its response to TRH also became normal in these cases. An elevated basal serum TSH value is thus highly indicative of subsequent hypothyroidism, and these subjects with symptomless autoimmune thyroiditis should be careully followed-up.