382 Sleep-Wake Disorders
asymptomatic individuals who snore and do not have abnorm alities on overnight polysom-
nography). Individuals with obstructive sl eep apnea hypopnea may additionally report
nocturnal gasping and choking. The presence of sleepiness or other daytime symptoms
not explained by other etiolo gies suggests the diagnosis of obstructive sleep apnea hypop-
nea, but this differentiation requires polysomnography. Defi nitive differential diagnosis
between hypersomnia, central sleep apnea, sleep-related hypoventilation, and obstructive
sleep apnea hypopnea also requ ires polysomnographic studies.
Obstructive sleep apnea hypopnea must be diff erentiated from other causes of sleepi-
ness, such as narcolepsy, hypersomnia, and ci rcadian rhythm sleep d isorders. Obstructive
sleep apnea hypopnea can be differentiated from  narcolepsy by the absence of cataplexy,
sleep-related hallucinations, and sleep paraly sis and by the presence of loud snoring,
gasping during sleep, or observed apneas in  sleep. Daytime sleep episodes in narcolepsy
are characteristically shorter,  more refreshing, and more of ten associated with dreaming.
Obstructive sleep apnea hypopnea shows characteristic apneas and hypopneas and oxy-
gen desaturation during nocturnal polysomnog raphic studies. Narcolepsy results in mul-
tiple sleep-onset rapid eye movement (REM) periods during the MS LT. Narcolepsy, like
obstructive sleep apnea hypopnea, may be asso ciated with obesity, and some individuals
have concurrent narcolepsy and obstructive sleep apnea hypopnea. A diagnosis of narco-