Screening for hypothyroidism in sleep apnea.

Primary sleep apnea-hypopnea syndrome (obstructive sleep apnea [OSA]) and hypothyroidism have many signs and symptoms in common. The overlap in clinical presentation, and the sleep-disordered breathing that can accompany hypothyroidism, create a significant risk of misdiagnosis of sleep apnea among patients referred to sleep clinic who have undiagnosed hypothyroidism. We determined the point prevalence of hypothyroidism in our sleep clinic patients with newly diagnosed sleep-disordered breathing. Of 290 sequential patients referred to sleep clinic, 200 (69%) patients judged at high risk for OSA underwent polysomnography (PSG) and biochemical screening for hypothyroidism. Of these, 124 (62%) were judged to have sleep apnea. This included three patients (1.5% of patients undergoing PSG or 2. 4% of those judged to have OSA) who were also discovered to have previously undiagnosed hypothyroidism. These three patients with "secondary" sleep apnea were treated with thyroxine therapy alone, and followed with sequential sleep studies and serum thyroid hormone assays; symptoms, sleep-disordered breathing, nocturnal hypoxia, and thyroid deficiency resolved simultaneously. We conclude that biochemical screening for hypothyroidism is required to prevent inadvertent misdiagnosis of hypothyroid sleep-disordered breathing as primary sleep apnea, and that it is a cost-effective component of the investigation of sleep apnea.