Update on Subclinical Hyperthyroidism

Subclinical hyperthyroidism is defined by low or undetectable serum thyroid-stimulating hormone levels, with nor - mal free thyroxine and total or free triiodothyronine levels. It can be caused by increased endogenous production of thyroid hormone (as in Graves disease or toxic nodular goiter), administration of thyroid hormone for treatment of malignant thyroid disease, or unintentional excessive thyroid hormone therapy. The rate of progression to overt hyperthyroidism is higher in persons who have suppressed thyroid-stimulating hormone levels compared with those who have low but detectable levels. Subclinical hyperthyroidism is associated with an increased risk of atrial fibrilla - tion in older adults, and with decreased bone mineral density in postmenopausal women; however, the effectiveness of treatment in preventing these conditions is unknown. There is lesser-quality evidence suggesting an association between subclinical hyperthyroidism and other cardiovascular effects, including increased heart rate and left ven- tricular mass, and increased bone turnover markers. Possible associations between subclinical hyperthyroidism and quality of life parameters, cognition, and increased mortality rates are controversial. Prospective randomized con- trolled trials are needed to address the effects of early treatment on potential morbidities to help determine whether screening should be recommended in the asymptomatic general population. (Am Fam Physician. 2011;83(8):933-938. Copyright © 2011 American Academy of Family Physicians.) ▲ Patient information: A handout on subclinical hyperthyroidism, written by the authors of this article, is provided on page 943.