Long-term study in subclinical hypothyroidism: spontaneous course and predictors of overt hypothyroidism

The syndrome of subclinical hypothyroidism is frequent and predominantly af fects females over 40. Only limited data on its natural course is available . It was the aim of our prospective trial to analyze the spontaneous evolut ion of this syndrome, to identify risk factors of the development of overt hypothyroidism and to develop guidelines for the management of such patient s. 154 female patients were followed over a mean observation period of 10 y ears. After 10 years, 34% had developed overt hypothyroidism, 57% remained in the subclinical stage, and in 9% thyroid function had normalized. The in itial grading of TSH-concentration (<6 mU/l, 6-12 mU/l, >12 mU/l)was highly predictive for thyroid failure: 7.3%, 25% and 78%, respectively, overt hyp othyroidism occurred. Further risk factors for thyroid failure included an impaired thyroid reserve (T-3-stimulation after TRH) and elevated titers of microsomal antibodies. We therefore recommend to controlling patients with a TSH-concentration <6 mU/l, start thyroxine hormone replacement therapy i n patients with a TSH-concentration >12 mU/l and, depending on the addition al risk factors, either controlling or treating patients with a TSH-concent ration of 6-12 mU/l.