A 42-year-old man comes to his primary care physician due to daytime sleepiness. He often falls asleep during meetings and while watching television and has even fallen asleep while driving. The patient does not feel refreshed when waking and has occasional morning headaches. He has not had abnormal dreams or visual hallucinations when falling asleep or on waking. The patient has no significant past medical history and is a lifetime non-smoker. He drinks 2 or 3 beers on Friday nights. Blood pressure is 148/100 mm Hg and pulse is 78/min and regular; BMI is 32 kg/m². Cardiopulmonary examination shows no abnormalities. Arterial blood gas analysis is normal. What is this patient's most likely diagnosis?

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11ec160b_3b3f_549d_9249_afa3e650e691_MD0001_00 This patient has several features that suggest obstructive sleep apnea (OSA), including daytime somnolence, nonrestorative sleep, and elevated blood pressure in the setting of underlying obesity. OSA is caused by closure of the upper airway due to relaxation of pharyngeal muscle tone during sleep. Additional contributing factors include obesity, tonsillar hypertrophy, and hypothyroidism. When the airway is occluded, PO₂ declines and PCO₂ rises until chemoreceptors in the carotid body and brainstem trigger arousal and pharyngeal tone returns. Sleep is repeatedly disrupted throughout the night, even in the absence of cortical awareness. Typical symptoms include excessive daytime sleepiness, morning headaches, cognitive impairment, and depression. Most patients also experience loud snoring due to partial closure of the airway. Chronic OSA can lead to systemic and pulmonary hypertension with right heart failure and an increased risk for cardiac arrhythmias. (Choice A) Central sleep apnea is due to diminished respiratory drive from a neurologic disorder. Symptoms may superficially resemble OSA, but it is usually associated with significant underlying chronic illness (eg, congestive heart failure, cerebrovascular disease, renal insufficiency) and is not more common in obesity. (Choice B) Narcolepsy is characterized by poorly regulated rapid eye movement (REM) sleep. It frequently causes excessive daytime sleepiness, but patients also suffer from cataplexy, sleep attacks, hypnagogic/hypnopompic hallucinations, and sleep paralysis. (Choice C) Obesity hypoventilation syndrome (Pickwickian syndrome) is caused by restricted expansion of the chest wall due to severe obesity. This leads to hypoventilation with a chronically elevated PCO₂ and reduced PO₂. This patient's normal blood gases and mild obesity are not consistent with obesity hypoventilation. (Choice E) Patients with simple insomnia may have daytime fatigue, but nonrestorative sleep, morning headaches, and elevated blood pressure suggest OSA. (Choice F) Restless leg syndrome is characterized by vague discomfort in the limbs that is brought on when trying to sleep and relieved with movement. Symptoms may recur through the night and lead to nonrestorative sleep, but patients are usually aware of the symptoms. Educational objective: Obstructive sleep apnea is due to relaxation of oropharyngeal muscle tone with occlusion of the upper airway. Symptoms include daytime sleepiness, headaches, and depression. Complications include systemic and pulmonary hypertension, right heart failure, and an increased risk for cardiac events. __________ References: Pathophysiology of obstructive sleep apnea. (http://www.ncbi.nlm.nih.gov/pubmed/18784537)

A 42-Year-Old Man Comes to His Primary Care Physician Due