1. A 45-year-old man presents with excessive daytime

sleepiness, loud snoring, and witnessed apneas. He has a

body mass index of 32 kg/m2 and a neck circumference of

17 inches. He undergoes a polysomnography, which

shows an apnea-hypopnea index of 25 events per hour,

with oxygen desaturation to 85%. What is the most likely

diagnosis?

A) Obstructive sleep apnea

B) Central sleep apnea

C) Narcolepsy

D) Idiopathic hypersomnia

*E) Obesity hypoventilation syndrome

Rationale: Obesity hypoventilation syndrome (OHS) is a

condition characterized by chronic daytime hypercapnia,

sleep-disordered breathing, and obesity. OHS is diagnosed

when the arterial carbon dioxide pressure (PaCO2) is

greater than 45 mmHg during wakefulness. OHS patients

typically have severe obstructive sleep apnea (OSA), but

OSA alone does not cause daytime hypercapnia. Central

sleep apnea, narcolepsy, and idiopathic hypersomnia are

not associated with obesity or hypercapnia.