Clinical Case Reports
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SP is a transient episode of muscle atonia that occurs during the transition between sleep and wakefulness, manifesting as immobility despite preserved consciousness. Isolated SP may occur in healthy individuals, however recurrent SP is a well-documented feature of narcolepsy. There is limited literature describing the polysomnographic features of SP, partly owning to its rarity and unlikelihood of being captured during a single study. We aim to illustrate the key neurophysiological features in a patient experiencing SP.
We report a 24-year-old female who presented to our sleep clinic for excessive daytime somnolence and recurrent SP episodes upon awakening from naps. She denied having episodes of cataplexy.
Results/ Case Presentation:
Multiple sleep latency test (MSLT) was consistent with narcolepsy. She reported one episode of SP which was captured on MSLT arising from her final sleep-onset REM period (SOREMP). Initially, she was in REM-sleep, reflected by theta-predominant EEG and suppressed chin EMG tone. She transitioned to wakefulness, reflected by alpha-predominant EEG, however, chin EMG tone remained suppressed, consistent with SP. Upon resolution of her SP episode, there was gradual increase in chin-EMG tone, followed by bursts of muscle tone enhancement.
Our patient’s MSLT tracing displays mutual existence of REM and wake EEG features occurring in tandem with persistent muscle atonia on chin EMG. This underlies the clinical experience of immobility despite transitioning from REM-sleep to wakefulness. SP is most common within the first 2 hours of sleep-onset or within the hours prior to awakening, corresponding to when timing of SOREMPs and REM-sleep predominate, respectively.
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