Cardiac manifestations. Subclinical hypothyroidism may be associated with ventricular dysfunction, myocardial infarction, and atherosclerosis.18-20 A randomized controlled trial of 20 people with subclinical hypothyroidism found significantly improved left ventricular function assessed by echocardiography after 6 months of treatment with levothyroxine vs placebo.18 Whether treatment prevents myocardial infarction and atherosclerosis is unknown.19,20 A cohort study, involving 2779 adults studied aged >20 years, did not find an association between subclinical hypothyroidism and ischemic heart disease.2
Risks of replacement. A meta-analysis of 41 controlled, cross-sectional studies involving 1250 women treated with thyroid replacement for all causes (ie, not specifically subclinical hypothyroidism) found that replacement therapy (mean duration of treatment, 7 to 9 years) was associated with bone loss in premenopausal women, but not in postmenopausal women.17
A randomized trial of 37 patients over 55 with subclinical hypothyroidism (28 of whom were women), found that thyroid hormone reduced bone mineral density, as assessed by dual-energy x-ray absorptiometry (DEXA) scans over a 10-month period.14 In several trials, patients withdrew due to adverse effects. Two of 37 patients receiving L-thyroxine in 1 study withdrew because of new atrial fibrillation and worsened angina, and 2 of 20 patients in another study withdrew because of nervousness and palpitations.13,14
Recommendations from others
The US Preventive Services Task Force concluded the evidence is insufficient to recommend for or against routine screening for thyroid disease in adults. The yield of screening is greater in high-risk groups such as postpartum women, people with Down syndrome, and the elderly; however, there is poor evidence that screening these groups leads to clinically important benefits.21
The American Thyroid Association recommends screening men and women beginning at age 35 and every 5 years thereafter.22 The American Academy of Family Physicians recommends screening for men and women over age 60.23 The American College of Physicians states screening may be indicated in women over age 50.24
CLINICAL COMMENTARY:
Consider screening all female patients, particularly those over age 50
Julian T. Hsu, MD
A.F. Williams Family Medicine Center, University of Colorado Health Sciences Center, Denver
In my practice, there recently seems to be increased pressure from patients to screen for hypothyroidism, perhaps based on media or Internet information. I have used an individual “risk factor” approach when patients ask me for testing, based on their age, family history, and current symptoms. Based on the data, using the history and physical examination to tailor screening is an ineffective method of detecting hypothyroidism.
Until we have more evidence, I believe a reasonable approach is to offer screening to all of our female patients, particularly those over age 50, along with a careful acknowledgment of the lack of data for or against screening.