Narcolepsy Is Characterized by the Presence of Excessive Daytime Sleepiness and Clinical Manifestations of Dissociated Rapid Eye

NARCOLEPSY IS CHARACTERIZED BY THE PRESENCE OF EXCESSIVE DAYTIME SLEEPINESS AND CLINICAL MANIFESTATIONS OF DISSOCIATED RAPID EYE MOVEMENT (REM) sleep including cataplexy, hypnagogic and hypnopompic hallucinations, and sleep paralysis.1 Normal REM sleep is characterized by tonic features, including cortical EEG desynchronization and muscle atonia, and phasic events, including bursts of rapid eye movements, phasic activities of both chin and limb EMG, and cardiorespiratory variability.2 Abnormalities in REM sleep motor regulation have been described in narcolepsy, including persistence of muscle tone, excessive twitching, and periodic leg movements during sleep (PLMS).3-5 The presence of REM sleep without atonia associated with prominent motor behavioral manifestations associated with dreaming during REM sleep is the key feature of a condition called REM sleep behavior disorder (RBD).6 RBD may occur alone and is then called “idiopathic” RBD. However, it is often associated with other neurological diseases such as lesions of the brainstem, neurodegenerative disease, especially synucleinopathies, and narcolepsy.7-9 In these latter cases, it is termed “secondary RBD.” Patients with narcolepsy and those diagnosed with RBD share several common polygraphic features, especially signs of REM sleep dysregulation. Both have increased PLMS at night with a specific increase of PLMS in REM sleep10-11; both have dissociated manifestations of REM sleep with a loss of REM sleep muscle atonia in RBD and the inappropriate occurrence of atonia during wakefulness (cataplexy) in narcolepsy.1,3-5 The loss of hypocretin neurons within the lateral hypothalamus causes narcolepsy in humans.12 Recent results based on detailed anatomy and lesion experiments in rats have identified independent pathways in brainstem that mediate the atonia and EEG phenomena of REM sleep.13 As hypocretin neurons are excitatory and active during wakefulness with strong projections to the brainstem structures implicated in REM sleep motor regulation,14 decreased hypocretinergic tone may cause REM sleep without atonia and RBD in humans. The aim of the present study was to assess in narcoleptic patients the REM sleep characteristics known to be impaired in RBD: REM sleep without atonia, REM sleep chin EMG phasic activities, and REM density, and to compare these results with results obtained in patients with RBD and normal controls. REM Sleep Characteristics in Narcolepsy and REM Sleep Behavior Disorder