Clinical neurophysiology of REM parasomnias: Diagnostic aspects and insights into pathophysiology

Abstract

Parasomnias are due to a transient unstable state dissociation during entry into sleep, within sleep, or during arousal from sleep, and manifest with abnormal sleep related behaviors, perceptions, emotions, dreams, and autonomic nervous system activity. Rapid eye movement (REM) parasomnias include REM sleep behavior disorder (RBD), isolated recurrent sleep paralysis and nightmare disorder. Neurophysiology is key for diagnosing these disorders and provides insights into their pathophysiology. RBD is very well characterized from a neurophysiological point of view, also thank to the fact that polysomnography is needed for the diagnosis. Diagnostic criteria are provided by the American Academy of Sleep Medicine and video-polysomnography guidelines for the diagnosis by the International REM Sleep Behavior Disorder Study Group. Differences between the two sets of criteria are presented and discussed. Availability of polysomnography in RBD provides data on sleep electroencephalography (EEG), electrooculography (EOG) and electromyography (EMG). Sleep EEG in RBD shows e.g. changes in delta and theta power, in sleep spindles and K complexes. EMG during REM sleep is essential for RBD diagnosis and is an important neurodegeneration biomarker. RBD patients present alterations also in wake EEG, autonomic function, evoked potentials, and transcranial magnetic stimulation. Clinical neurophysiological data on recurrent isolated sleep paralysis and nightmare disorder are scant. The few available data provide insights into the pathophysiology of these disorders, demonstrating a state dissociation in recurrent isolated sleep paralysis and suggesting alterations in sleep macro- and microstructure as well as autonomic changes in nightmare disorder.

Keywords: Electroencephalography; Electromyography; Electrooculography; Nightmare disorder; RBD; REM sleep; REM sleep behavior disorder; Recurrent isolated sleep paralysis.

Fig. 1

REM sleep without atonia. The figure shows a 30-s polysomnography page of a RBD patients with REM sleep without atonia. The electrooculography channels (Au) show rapid eye movements. The EEG channels (F3-M2, F4-M1, C3-M2, C4-M1, O1-M2, O2-M1) show the low-amplitude mixed frequency activity typical of REM sleep. The EMG channels show excessive muscle activity in particular in the limbs. Abbreviations: Au-hor-L: Electrooculography horizontal left; Au-hor-R: electrooculography horizontal right; Au-ver-L: Electrooculography vertical left; Au-ver-R: electrooculography vertical right; ECG: electrocardiography; EEG, electroencephalography; ment: muscle mentalis; MFD-L: muscle flexor digitorum superficialis left; MFD-R: muscle flexor digitorum superficialis right; NAC-L: muscle stenocleidomastoideus left; NAC-R: muscle stenocleidomastoideus right; subment: muscle submentalis; Tib-L: muscle tibialis anterior left; Tib-R: muscle tibialis anterior right.