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Routine thyroid screening is not recommended for patients suspected of having obstructive sleep apnea

Obstructive sleep apnea (OSA) and hypothyroidism (underactive thyroid) are relatively common disorders that have similar symptoms, such as breathing problems during sleep and daytime lethargy. It has been suggested that hypothyroidism might cause OSA, leading many clinicians to wonder if they should perform thyroid screening for patients with OSA. However, a recent study shows that only 1.41 percent of patients without a prior history of hypothyroidism who underwent polysomnography and thyroid function testing were found to have subclinical hypothyroidism. The study was supported in part by the Agency for Health Care Policy and Research (National Research Service Award fellowship F32 HS00109) and led by Vishesh K. Kapur, M.D., of the University of Washington, Seattle.

A more practical approach may be to limit thyroid testing to individuals who fail to show sleep-disordered breathing of sufficient severity to explain their symptoms, who do not show satisfactory improvement after effective therapy for sleep-disordered breathing, or in whom hypothyroidism is suspected based on physical exam, notes Dr. Kapur. The researchers reviewed the medical charts of 336 adult patients at a health maintenance organization who underwent polysomnography for suspected OSA. They determined patients' thyroid function status, polysomnography results, use of levothyroxine to reduce sleep-disordered breathing, and clinical signs and symptoms. Most of the patients had a history of snoring, episodes of sleep apnea (temporary cessation of breathing) witnessed by others, or daytime sleepiness.

Based on testing performed during or after the initial visit for a sleep complaint, only four patients (1.41 percent) were found to have previously undiagnosed subclinical hypothyroidism, and their only symptoms were fatigue and snoring. It is not known whether subclinical hypothyroidism causes OSA or that treating hypothyroidism would cure coexisting OSA. Even in patients with overt hypothyroidism and OSA, the effect of thyroid hormone replacement on sleep-disordered breathing has been variable, concludes Dr. Kapur.

See "Association of hypothyroidism and obstructive sleep apnea," by Dr. Kapur, Thomas K. Koepsell, M.D., M.P.H., James deMaine, M.D., and others, in the American Journal of Respiratory and Critical Care Medicine 158, pp. 1379-1383, 1998.

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