410 Sleep-Wake Disorders
Obstructive sleep apnea. Obstructive sleep apnea may result in behaviors indistin-
guishable from REM sleep behavior disorder . Polysomnographic monitoring is necessary
to differentiate between the two. In this ca se, the symptoms resolv e following effective
treatment of the obstructive sleep apnea, and REM sleep without atonia is not present on
polysomnography monitoring.
Other specified dissociative disorder (sleep-related psychogenic dissociative disorder).
Unlike virtually all other parasomnias, which arise precipitously from NREM or REM
sleep, psychogenic dissociative behaviors aris e from a period of well-defined wakefulness
during the sleep period. Unlike REM sleep behavi or disorder, this condition is more prev-
alent in young females.
Malingering. Many cases of malingering in which the individual reports problematic
sleep movements perfectly mimic the clinical features of REM sleep behavior disorder,
and polysomnographic documentation is mandatory.
Comorbidity
REM sleep behavior diso rder is present concurrently in  approximately 30% of patients
with narcolepsy. When it occurs in narcolep sy, the demographics reflect the younger age
range of narcolepsy, with equal frequency in  males and females. Based on findings from
individuals presenting to sleep clinics, most individuals (>50%) with initially “idiopathic”
REM sleep behavior disorder will eventually develop a neurodegenerative disease—most
notably, one of the synucleinopathies (Parkins on’s disease, multiple system atrophy, or
major or mild neurocognitive disorder with Lewy bodies).  REM sleep behavior disorder
often predates any other sign of these disorder s by many years (often more than a decade).
Relationship to Internat ional Classification of 
Sleep Disorders