Subclinical thyroid disease: subclinical hypothyroidism and hyperthyroidism

Subclinical hypothyroidism (SHT) and subclinical hyperthyroidism (SCH) are defined as normal serum free T4 and T3 levels associated with elevated (SHT) or subnormal (SCH) serum TSH levels, respectively. Symptoms and signs of thyroid dysfunction are scarce. The prevalence is low. In SHT, total cholesterol and LDL-C are modestly elevated and levothyroxine may influence the lipids levels. There is decreased cardiac contractility and increased peripheral vascular resistance that improve with treatment. SCH is associated with atrial fibrillation, increased cardiac contractility and left ventricular mass, diastolic and systolic dysfunction that can be reversed with beta-adrenergic antagonists. Bone density is reduced in SCH. Depression, panic disorders and alterations in cognitive testing are frequent in SHT. Treatment of SHT is recommended for serum TSH levels greater than 8 mU/L and presence of thyroid antibodies. Endogenous SCH should be treated for serum TSH levels less than 0.1 mU/L, in the presence of symptoms and in elderly patents.