Narcolepsy 377
guished based on distinctive clinical and labo ratory features. Individuals with hypersom-
nolence typically have longer and less disrupted nocturnal sleep, greater difficulty
awakening, more persistent daytime sleepine ss (as opposed to more discrete “sleep at-
tacks” in narcolepsy), longer and less refreshing daytime sleep episodes, and little or no
dreaming during daytime naps. By contrast, individuals with narcolepsy have cataplexy
and recurrent intrusions of elements of REM sleep into the transition between sleep and
wakefulness (e.g., sleep-related hallucination s and sleep paralysis). The MSLT typically
demonstrates shorter sleep latenc ies (i.e., greater physiological  sleepiness) as well as the
presence of multiple sleep-onset REM periods in individuals with narcolepsy.
Sleep deprivation and insufficient nocturnal sleep. Sleep deprivation and insufficient
nocturnal sleep are common in adolescents and shift workers. In adolescents, difficulties
falling asleep at night are common, causing sleep deprivation. The MSLT result may be
positive if conducted while the individual is  sleep deprived or while his or her sleep is
phase delayed. 
Sleep apnea syndromes. Sleep apneas are especially likely in the presence of obesity.
Because obstructive sleep apnea is more freque nt than narcolepsy, ca taplexy may be over-
looked (or absent), and the individual is as sumed to have obstructive sleep apnea unre-
sponsive to usual therapies. 
Major depressive disorder. Narcolepsy or hypersomnia may be associated or confused
with depression. Cataplexy is not present in depression. The MSLT re sults are most often
normal, and there is dissociation between subj ective and objective sleepiness, as measured