How is multiple sleep latency testing (MSLT) performed in polysomnography (PSG)?

Updated: Apr 29, 2020
  • Author: Carmel Armon, MD, MSc, MHS; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Multiple sleep latency testing (MSLT) is used to assess the degree of daytime sleepiness and to evaluate for possible narcolepsy. MSLT should be performed after a full-night polysomnogram to ensure that at least 6 hours of sleep precede the test and that no other causes for excessive daytime sleepiness are present. A sleep log should be kept for at least 1 week prior to the study, and all medications taken for the 2 weeks prior to the study should be noted. Urine drug testing is often done to evaluate for drugs that may affect study results. Stimulant medications, nicotine, and caffeine can affect the mean sleep latency, and medications (especially selective serotonin reuptake inhibitors [SSRIs]) can affect sleep-onset rapid eye movement (REM) periods. [7] In general, SSRIs and stimulants need to be discontinued at least 2 weeks prior to the test. Small amounts of caffeine do not usually need to be discontinued.

The patient is given 20 minute opportunities to nap every 2 hours for 4 or 5 naps. The first nap should begin within 1.5-3 hours after waking. If the patient falls asleep, he or she is allowed to sleep for 15 minutes. Sleep latency is the time to the first epoch with over 15 seconds of any stage of sleep. The mean sleep latency is determined. A mean sleep latency of 10-15 minutes is consistent with mild sleepiness, 5-10 minutes is consistent with moderate sleepiness, and less than 5 minutes is consistent with severe sleepiness. A series of 2 sleep-onset REM periods (SOREMP) is consistent with the diagnosis of narcolepsy; however, only 80% of patients with narcolepsy and 6.6% of patients without narcolepsy had 2 or more SOREMPs in a review of over 2000 MSLTs.


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