Teaching NeuroImages: Sleep-onset REMperiod during routine EEG

A 76-year-old incarcerated man presented with word-finding difficulties and underwent a routine EEG. Shortly after reaching stage N2 sleep, EEG showed brisk lateral eye movements with concurrent sawtooth waves (figure), indicating sleep-onset REM period (SOREMP). Normal REM sleep is reached 90–120 minutes after sleep onset. SOREMP is an abnormal EEG finding thought to be suggestive of narcolepsy. However, it may also be present in 3.9% of the general population1 and is normal in infants. It is also associated with severe sleep deprivation, obstructive sleep apnea, and alcohol or medication (selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, tricyclic antidepressants, monoamine oxidase inhibitors) withdrawal. In the inpatient setting, it is usually caused by sleep deprivation.2