Hipotiroidismo subclínico

Subclinical hypothyroidism is characterized by elevation of thyrotropin (TSH) concentrations with normal circulating concentrations of thyroid hormones. This mild thyroid failure is common in the general population, especially among elderly women. Patients with moderate subclinical hypothyroidism may progress to overt hypothyroidism, although other patients may show normalization of TSH concentrations or persistence of elevated serum TSH. The main risk factors for the development of overt thyroid failure in patients with subclinical hypothyroidism are TSH levels greater than 10 mU/l, thyroid autoimmunity, and a history of thyroid disease or thyroid treatments. Pharmacological therapy can be started in subclinical thyroid hypofunction to alleviate symptoms, improve lipid profile and cardiac function, ameliorate premature atherosclerotic changes, and prevent progression to overt disease. Replacement therapy with thyroxine is not without risks. Some concerns are the lack of benefit, and the need for life long medication and medical monitoring. Over-replacement with thyroxine is associated with the known adverse effects of thyrotoxicosis on bone mass and the cardiovascular system. Most authorities and scientific societies recommend starting thyroxine replacement therapy in patients with TSH concentrations higher than 10 mU/l. Patients who are pregnant, or who have symptoms of hypothyroidism, goiter, positive thyroid autoimmunity or progressive elevation of TSH levels can also to be considered for therapy, even when TSH concentrations are below 10 mU/l.