[Subclinical hypothyroidism as a cause of reversible cognitive deterioration].

Hypothyroidism, which is treatable by hormone substitution, is one of the most frequent causes of symptomatic dementia. The effectiveness of hormone therapy for improving mental status is well established, but full reversibility of symptoms is unusual. We report the case of a woman whose disease began with progressive cognitive deterioration and tremor; laboratory tests revealed subclinical hypothyroidism, which was watched carefully over the next three years. When thyroid hormone therapy was begun, there was marked clinical improvement, which reversed only when the patient voluntarily withdrew treatment for a few weeks.