Subclinical thyroid dysfunction in the elderly.

Subclinical thyroid dysfunction is more common in older persons. By definition, these disorders are recognized by isolated elevation or suppression of the serum TSH concentration, in association with a normal serum free thyroxine level. Among individuals over 65 years old, subclinical hypothyroidism is found in approximately 10% of women and approximately 3% of men. It is most commonly due to autoimmune thyroiditis or previous treatment for hyperthyroidism. There may be three indications for L-thyroxine therapy: (a) presence of antithyroid antibodies, indicating substantial risk of progression to over hypothyroidism; (b) symptoms consistent with thyroid hormone deficiency; and (c) an elevated serum LDL-cholesterol. Subclinical hyperthyroidism is present in approximately 1%-2% of older persons. The most common cause is excessive thyroid hormone therapy, followed by mild endogenous hyperthyroidism due to Graves' disease or nodular goiter. These can be differentiated from other causes of low serum TSH concentration based on clinical and other laboratory and radionuclide scan criteria. The most serious consequences of subclinical hyperthyroidism are atrial fibrillation and osteoporosis, to which elderly patients are particularly predisposed.