SOURCE: Stott DJ, et al. N Engl J Med 2017;376:2534-2544.

Subclinical hypothyroidism (SCH) is defined as an elevation in thyroid-stimulating hormone (TSH) in the presence of normal levels of thyroxine. When thyroxine drops to subnormal levels in the company of elevated TSH, primary hypothyroidism is diagnosed. Since SCH often is a stepping stone to overt hypothyroidism, it is tempting to offer treatment for it. But does treatment of SCH improve outcomes?

By definition, patients with SCH are not supposed to be symptomatic of hypothyroidism; otherwise, the syndrome could not be called “subclinical.” But might restoration of full chemical euthyroid status provide a boost to energy, well-being, or other quality-of-life attributes? Stott et al performed a double-blind, randomized, controlled trial in older adults (mean age = 74 years) with SCH comparing levothyroxine supplementation to placebo (n = 737). Outcomes at one year included hypothyroid symptom scores, fatigue measurements, and quality-of-life outcomes. Although levothyroxine supplementation provided meaningful reductions of TSH into the normal range, there was no statistically significant improvement in any of the symptom outcomes. Additionaly, since levothyroxine supplementation proved quite safe, these data should discourage clinicians from treating elevations of TSH unless thyroxine levels also are subnormal.