Procedure of the MSLT

The MSLT is routinely performed at 2-hr intervals, beginning 1.5-3 hr after awakening from nocturnal sleep, and consists of 4-6 naps. Subjects should be in bed 5 min before the scheduled start of the test, to allow for calibrations of the 

The underlying assumption of the MSLT is that lower scores indicate greater sleepiness and vice versa. A common rubric holds that a daily average score of less than 5 min indicates a pathological level of daytime sleepiness. This level is associated with impaired performance in patients and in sleep-deprived normal subjects (26). Scores of adult normal controls usually range from 10 to 20 min (27). Scores between 5 and 10 min indicate moderate sleepiness, and may or may not be associated with pathological conditions (23). 

Abnormal sleep-onset REM periods, which occur within 15 min of sleep onset, are of major importance in the diagnosis of narcolepsy. Other causes of sleep-onset REM periods, such as sleep deprivation or other sleep disorders (e.g., obstructive sleep apnea), must be excluded (28). 

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