To Screen or not to Screen for Subclinical Thyroid Disorders?

What are subclinical thyroid disorders? As expected there are 2, subclinical hypothyroidism and subclinical hyperthyroidism. They are defined as elevated or decreased thyroid-stimulating hormone (TSH) levels in patients, respectively, that have normal thyroid hormone levels and no signs of frank hormone deficiency or overactivity by history and examination. The only way to identify the subclinical varieties of thyroid dysfunction is to screen asymptomatic individuals with TSH. Since prescriptions for thyroid replacements have increased from 49.8 million (2006) to 70.5 million (2010), primary care providers must be screening.¹ Looking at individuals older than 65 years, the number taking thyroid replacement has increased from 8.1% to 20.0% between 1989 and 2005.¹ The million dollar question must be asked: Are we doing any good with this strategy of screen and treat?

This month’s Top Paper¹ seems to answer in the negative. Despite suspicion that subclinical hypothyroidism and hyperthyroidism might increase cardiovascular disease, damage cognitive function, lead to weight gain, atrial fibrillation, and fractures, the data does not support it.

• There is no definitive evidence that thyroid replacement improves clinical outcomes as a consequence of cardiovascular disease and heart failure.

• No association has been found between replacement and improvements in cognitive functioning.

• How many times have you been told that weight gain comes from an underactive thyroid? No recent trials have demonstrated weight loss as a benefit of thyroid hormone treatment of subclinical hypothyroid persons.

• One trial showed downsides of replacement with patients “feeling worse” after prescription and some folks with occasional angina and atrial fibrillation.

• Two studies identified 40% of “subclinical” hypothyroid patients on follow-up were euthyroid after 3 years of watching without therapy.

• There are no well-designed studies with statistically significant data showing harms from untreated subclinical hyperthyroidism. It is possible that this entity might increase the risk of hip and nonspine fractures.²

There may be some exceptions to the data. A quote from another recent paper³: “Meanwhile, for subclinical thyroid disease, while routine treatment remains controversial, routine screening with TSH levels merits implementation, especially in pregnant women, women over 60 years of age, and anyone whose risk of thyroid dysfunction is high.” Another opinion also observed, “Multiple studies have demonstrated an increased risk of atrial fibrillation, especially in older individuals with TSH levels of 0.1 mU/L.⁴

Bottom line, I think we are overdoing the screening and treatment of subclinical thyroid disorders. There may be special circumstances that require screening and even treatments, but the numbers are far less than those individuals screened and treated today. ■

Gregory W. Rutecki, MD, is a physician at the National Consult Service at the Cleveland Clinic. He is also a member of the editorial board of Consultant. Dr Rutecki reports that he has no relevant financial relationships to disclose.

References:

1. Rugge JB, Bougatsos C, Chou R. Screening and treatment of thyroid dysfunction: an evidence review for the U.S. Preventive Services Task Force. Ann Intern Med. 2015;162(1):35-45.

2.  Wirth CD, Blum MR, da Costa BR, et. al. Subclinical thyroid dysfunction and the risk for fractures: a systematic review and meta-analysis. Ann Intern Med. 2014;161(3):189-199.  

3.  Grais IM, Sowers JR. Thyroid and the heart. Am J Med. 2014;127(8):691-698.

4.  Palmeiro C, Davila MI, Bhat M, et. al. Subclinical hyperthyroidism and cardiovascular risk: recommendations for treatment. Cardiol Rev. 2013;21(6):300-308.