Key Points for Practice
• Thyroid hormones do not improve quality of life or thyroid-related symptoms in patients with subclinical hypothyroidism.
• In older patients, treatment of subclinical hypothyroidism does not improve muscle strength or cognitive function, but could increase mortality.
• In patients who are pregnant and in those with a TSH level greater than 20 mIU per L, severe symptoms, or age 30 years or younger, the benefit of subclinical hypothyroidism treatment is unknown.
From the AFP Editors
Subclinical hypothyroidism is a state of contradiction, with an elevated thyroid-stimulating hormone (TSH) level suggesting hypothyroidism but a normal free thyroxine level. Symptoms that suggest hypothyroidism may or may not be present. Treatment of subclinical hypothyroidism has long been controversial because of normal increases in TSH with age, variability between TSH measurements, and concerns for harm from treatment.
Previous guidelines suggested that levothyroxine treatment may be appropriate with hypothyroid symptoms or a TSH level exceeding 10 mIU per L based on limited evidence. A recent large trial in older adults suggests that treatment shows no benefit in many areas and possible harm. The BMJ/MAGIC Group sought to determine whether treatment of subclinical hypothyroidism increases quality of life measures, improves symptoms, or induces harm.
People 65 Years and Older
Studies of subclinical hypothyroidism primarily include older people. Substantial evidence demonstrates that levothyroxine is not beneficial for patients 65 years and older. Symptoms suggesting hypothyroidism, such as fatigue and depression, are not improved with supplementation more than with placebo. Quality of life and body mass index are unchanged. Muscle strength and cognitive function are not enhanced. Harms such as cardiovascular events and mortality are not more frequent, although data suggest that larger studies may demonstrate these risks. With no benefit and concern for harm, the group recommends against treatment.
People Younger than 65 Years
Although fewer younger people have been studied, levothyroxine shows a similar lack of benefit for subclinical hypothyroidism. Treatment does not improve thyroid-related symptoms, quality of life, body mass index, muscle strength, or cognitive function. Because few deaths of younger patients were reported, the effect of treatment is unclear. The lack of benefit suggests that lifelong medication use and mistaking mood disorders for subclinical hypothyroidism could represent further harms.
The BMJ/MAGIC Group states that any benefit from treating subclinical hypothyroidism remains unknown in some patients. Subclinical hypothyroidism increases adverse pregnancy outcomes in retrospective analyses, but evidence is lacking on whether treatment reduces these harms. Patients with TSH levels greater than 20 mIU per L, which suggests overt hypothyroidism, and those with severe symptoms were not included in the studies. These studies included few people 30 years or younger, focusing more on an older population.
Editor's Note: The U.S. Preventive Services Task Force recommends against screening for thyroid disease based on lack of evidence of benefit. Even without screening, many patients present with symptoms of possible thyroid disease. Treatment has been suggested when TSH levels exceed 10 mIU per mL, but with little supporting evidence. The systematic review with this guideline provides the strongest evidence that levothyroxine treatment is not beneficial for subclinical hypothyroidism, and may be harmful for older people.—Michael J. Arnold, MD, contributing editor
Guideline source: BMJ/MAGIC Group
Evidence rating system used? Yes
Systematic literature search described? Yes
Guideline developed by participants without relevant financial ties to industry? Yes
Recommendations based on patient-oriented outcomes? Yes
Published source: BMJ. May 2019;365:l2006
Available at: https://www.bmj.com/content/365/bmj.l2006