[Subclinical thyroid dysfunction]

Abstract

Subclinical thyroid diseases are biologically defined: thyrotropin (TSH) decreased or increased with normal thyroid hormone concentrations. They are most often asymptomatics but carry a risk of long-term complications which can justify, in some cases, a treatment. The main complication of subclinical hyperthyroidism is atrial fibrillation, in particular after 60. Even if there is no controlled clinical trial available, treatment (usually with radioiodine) can be proposed to elderly subjects with autonomous thyroid disease (toxic adenoma or multinodular goitre) and TSH persistently below 0.1 mU/L. Subclinical hypothyroidism may be associated, particularly in subjects under 60, to a multifactorial increase of cardiovascular risk. An increase of TSH beyond 10 mU/L and positivity of antiTPO antibodies are the best predictors of the evolution toward overt hypothyroidism. In the elderly, there is no evidence of a risk associated with moderately increased TSH and treatment is probably not justified in most cases.