How is stage R scored in sleep stage scoring?

Updated: Aug 19, 2019
  • Author: Andres A Gonzalez, MD, MMM, FACNS; Chief Editor: Selim R Benbadis, MD  more...
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Stage R is scored in epochs that contain all of the following characteristics: the demonstration of rapid eye movements (REMs; irregular, conjugate, sharply peaked eye movements with an initial phase lasting less than 500msec detected in the EOG); EEG signals comprised of relatively low-amplitude and mixed-frequency activity; and muscle tone at the lowest of any stage in the polysomnogram as detected by EMG. [13]

Stage R. This demonstrates rapid eye movements, re Stage R. This demonstrates rapid eye movements, relatively low EMG tone, and low-voltage, mixed-frequency EEG activity.
Stage R. This demonstrates sawtooth waves. Stage R. This demonstrates sawtooth waves.

Epochs following stage R continue to be scored as stage R unless (1) there is a clear change to another sleep stage, (2) an arousal or major body movement followed by slow eye movements take place, or (3) K complexes or sleep spindles, hallmarks of stage N2 sleep, occur in the absence of REMs.

Stage R is the equivalent to the R and K Stage REM and is characterized by muscle atonia with rapid eye movements. Polysomnographic features that are supportive of but not required in stage R include sawtooth waves and phasic muscle twitches. Sawtooth waves are 2-6 Hz serrated bursts of activity, maximal centrally, that often, but not always, precede rapid eye movements. Phasic muscle twitches are brief bursts of irregular EMG activity lasting less than 0.25 msec, superimposed on a persistently low EMG tone, which may be detected on chin EMG, anterior tibialis EMG, or EOG-EEG leads. Muscle activity detected as EEG and EOG signals indicate activity of cranial nerve innervated muscles of the face and scalp.

There is special consideration given to the transition between N2 and REM stages. In a single epoch, if REMs are present with low chin EMG, the epoch is scored as Stage R even if sleep spindles and K complexes are present (this situation is more common in the first REM period of the night). If REMs are absent, chin tone is low, and K complexes/spindles are present, the epoch is Stage R when the K complex/spindle occurs in the second half of the epoch and N2 if they occur in the first half. The epoch following a Stage R epoch with a K complex/spindle in the second half is scored as N2 unless all three Stage R criteria are present. Any increase in muscle tone in conjunction with a K complex and/or spindle results in the epoch scored as N2. The epoch following a sleep spindle remains REM unless there is an associated muscle tone increase and development of slow eye movements.

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