[Long-term study of subclinical hypothyroidism: spontaneous course and predictors of manifest hypothyroidism].

The syndrome of subclinical hypothyroidism is frequent and predominantly affects females over 40. Only limited data on its natural course is available. It was the aim of our prospective trial to analyze the spontaneous evolution of this syndrome, to identify risk factors of the development of overt hypothyroidism and to develop guidelines for the management of such patients. 154 female patients were followed over a mean observation period of 10 years. After 10 years, 34% had developed overt hypothyroidism, 57% remained in the subclinical stage, and in 9% thyroid function had normalized. The initial 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 hypothyroidism occurred. Further risk factors for thyroid failure included an impaired thyroid reserve (T3-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 in patients with a TSH-concentration > 12 mU/l and, depending on the additional risk factors, either controlling or treating patients with a TSH-concentration of 6-12 mU/l.