Multiple Sleep Latency Test (MSLT)
Objective daytime protocol with scheduled naps, usually the day after polysomnography, to assess excessive daytime sleepiness.
Overview
Reference examination to objectively diagnose excessive daytime sleepiness. The examination, carried out in a sleep laboratory, generally the day after a night of polysomnography, typically includes 5 naps of 20 minutes each, spaced 2 hours apart.
Sleep latency and sleep-onset REM periods are measured to support diagnoses such as narcolepsy or idiopathic hypersomnia. Prior-night polysomnography ensures results are interpreted in the context of adequate sleep and without untreated sleep apnea.
Preparation
- Often scheduled the day after in-lab polysomnography.
- Medication and substance use documented beforehand.
- Standardised nap opportunities in a quiet, dark room.
- Interpretation aligned with international criteria.
Clinical role
MSLT complements history and questionnaires when subjective sleepiness must be quantified for diagnosis, occupational, or treatment decisions.