Subclinical Hyperthyroidism: When to Consider Treatment

 

Subclinical hyperthyroidism is defined by a low or undetectable serum thyroid-stimulating hormone level, with normal free thyroxine and total or free triiodothyronine levels. It can be caused by increased endogenous production of thyroid hormone (e.g., in Graves disease, toxic nodular goiter, or transient thyroiditis), by administration of thyroid hormone to treat malignant thyroid disease, or by unintentional excessive replacement therapy. The prevalence of subclinical hyperthyroidism in the general population is about 1% to 2%; however, it may be higher in iodine-deficient areas. The rate of progression to overt hyperthyroidism is higher in persons with thyroid-stimulating hormone levels less than 0.1 mIU per L than in persons with low but detectable thyroid-stimulating hormone levels. Subclinical hyperthyroidism is associated with an increased risk of atrial fibrillation and heart failure in older adults, increased cardiovascular and all-cause mortality, and decreased bone mineral density and increased bone fracture risk in postmenopausal women. However, the effectiveness of treatment in preventing these conditions is unclear. A possible association between subclinical hyperthyroidism and quality-of-life parameters and cognition is controversial. The U.S. Preventive Services Task Force found insufficient evidence to assess the balance of benefits and harms of screening for thyroid dysfunction in asymptomatic persons. The American Thyroid Association and the American Association of Clinical Endocrinologists recommend treating patients with thyroid-stimulating hormone levels less than 0.1 mIU per L if they are older than 65 years or have comorbidities such as heart disease or osteoporosis.

Subclinical hyperthyroidism is defined by a low or undetectable serum thyroid-stimulating hormone (TSH) level, with normal free thyroxine (T4) and total or free triiodothyronine (T3) levels.1 Subclinical hyperthyroidism can be divided into two categories: low but detectable TSH (usually 0.1 to 0.4 mIU per L) and less than 0.1 mIU per L.1 This article reviews the natural history of endogenous subclinical hyperthyroidism and its impact on cardiovascular events, bone and mineral metabolism, cognition, and quality of life. Since the most recent review on this topic,2  studies have strengthened the association between subclinical hyperthyroidism and the risk of cardiovascular disease and bone fractures (Table 1).17 Emerging evidence shows the benefits of treating subclinical hyperthyroidism in patients with TSH levels less than 0.1 mIU per L, particularly in older adults and patients at high risk of cardiovascular events and bone loss.

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SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Physicians should not routinely screen for subclinical thyroid disease.

C

1

To reduce the risk of atrial fibrillation, heart failure, and mortality, physicians should treat adults with subclinical hyperthyroidism who are 65 years or older and have TSH levels less than 0.1 mIU per L.

C

34

To decrease the risk of further bone loss, physicians should treat postmenopausal women with TSH levels less than 0.1 mIU per L and osteoporosis.

C

34


TSH = thyroid-stimulating hormone.

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendationEvidence ratingReferences

Physicians should not routinely screen for subclinical thyroid disease.

C

1

To reduce the risk of atrial fibrillation, heart failure, and mortality, physicians should treat adults with subclinical hyperthyroidism who are 65 years or older and have TSH levels less than 0.1 mIU per L.

C

34

To decrease the risk of further bone loss, physicians should treat postmenopausal women with TSH levels less than 0.1 mIU per L and osteoporosis.

C

34


TSH = thyroid-stimulating hormone.

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.

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BEST PRACTICES IN ENDOCRINOLOGY: RECOMMENDATIONS FROM THE CHOOSING WISELY CAMPAIGN

RecommendationSponsoring organization

Do not order multiple tests in the initial evaluation of a patient with suspected thyroid disease. Check thyroid-stimulating hormone level, and if abnormal, follow up with additional evaluation and treatment depending on the findings.

American Society for Clinical Pathology

Do not routinely order thyroid

The Authors

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INES DONANGELO, MD, PhD, is a staff endocrinologist at Allegheny Health Network, Pittsburgh, Pa., and an assistant professor of medicine at Drexel University College of Medicine, Philadelphia, Pa....

SE YOUNG SUH, MD, is an endocrinology fellow at Allegheny Health Network Medical Education Consortium, Pittsburgh.

Address correspondence to Ines Donangelo, MD, PhD, Allegheny Health Network, 320 E. North Ave., South Tower, 7th Fl., Pittsburgh, PA 15212 (e-mail: ines.donangelo@ahn.org). Reprints are not available from the authors.

Author disclosure: No relevant financial affiliations.

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