[Subclinical hypothyroidism]

Subclinical hypothyroidism, defined by elevated serum levels of thyroid stimulating hormone (TSH) with normal levels of free thyroid hormones, belongs to the most common disorders encountered in an endocrine office practice. It is assumed that elevated TSH levels in patients with subclinical hypothyroidism do not reflect pituitary compensation to maintain euthyroidism but probably represents a state of mild tissue hypothyroidism. Some patients with this condition experience subtle hypothyroid symptoms and have mild abnormalities of serum lipoproteins that may provoke atherosclerosis and cardiac dysfunction. Subclinical hypothyroidism is also associated with the risk of progression to overt hypothyroidism and with the risk of neuropsychiatric effects. For these reasons, subclinical hypothyroidism should be screened more carefully in the community. There is insufficient evidence that treatment ofsubclinical hypothyroidism is beneficial. Thyroxine therapy should be given if the serum TSH level is higher than 10 mIU/L but for lower TSH values, the decision for therapy should be individualized. This article reviews the epidemiology, etiopathogenesis, clinical presentation, diagnosis, and management of subclinical hypothyroidism. Based on the principles of evidence-based medicine, we provide some screening and treatment recommendations.