Rapid Eye Movement Sleep Behavior Disorder 409
toms in young individuals, particularly young females, should raise the possibility of
narcolepsy or medication-induced REM sleep behavior disorder. 
Risk and Prognostic Factors 
Genetic and physiological. Many widely prescribed medications, including tricyclic
antidepressants, selective serotonin reuptake inhibitors, serotonin-norepinephrine reup-
take inhibitors, and beta-blockers, may resu lt in polysomnographic evidence of REM sleep
without atonia and in frank REM sleep behavior disorder. It is not known whether the
medications per se result in REM sleep behavi or disorder or they unmask an underlying
predisposition.
Diagnostic Markers
Associated laboratory findin gs from polysomnography indicate increased tonic and/or
phasic electromyographic activi ty during REM sleep that is normally associated with mus-
cle atonia. The increased muscle activity variably affects different muscle groups, mandating
more extensive electromyographi c monitoring than is employed in conventional sleep stud-
ies. For this reason, it is su ggested that electrom yographic monitoring include the submen-
talis, bilateral extensor digito rum, and bilateral anterior tibi alis muscle groups. Continuous
video monitoring is mandator y. Other polysomnographic findings may include very fre-
quent periodic and aperiodic extremity el ectromyography acti vity during non-REM
(NREM) sleep. This polysomnography observation, termed REM sleep without atonia,  is pres-
ent in virtually all cases of REM sleep behavi or disorder but may also be an asymptomatic
polysomnographic finding. Clinical dream-enacting behaviors coupled with the polysom-
nographic finding of REM without atonia is necessary for the diagnosis of REM sleep behav-