Multiple Sleep Latency Test

What is a multiple sleep latency test (MSLT)?

The multiple sleep latency test (MSLT) is a diagnostic tool that measures the time it takes an individual to fall asleep in ideal quiet conditions during the day.  It objectively measures daytime sleepiness. Colloquially known as the daytime nap study, MSLT is also a standard tool used to diagnose idiopathic hypersomnia and narcolepsy.

The multiple sleep latency test takes a full day to complete, which includes four to five 20-minute naps scheduled throughout the day with two-hour breaks in between. 

 The MSLT is based on the fact that the more tired you are, the faster you will fall asleep.  In addition to assessing for narcolepsy and idiopathic hypersomnia, MSLT is used to determine whether the treatments being used for sleep breathing disorders, such as CPAP for sleep apnea, are working.

sleep study data

Once the lights are out, the test will measure the length of time it takes for you to fall asleep.  You will be awoken by the technologist 15 minutes later.  The nap trial will end if 20 minutes pass and you have not fallen asleep.  Each of the four or five naps are taken with a series of sensors that will determine if you have fallen asleep.  These sensors, consequently, also determine the sleep stages, as part of the MSLT is to look at brain patterns and REM sleep, which can be used to determine sleep problems.  During the test, your brain waves, muscle activity, and eye movements are also closely monitored and recorded.

Scores, while difficult to calculate, are relatively easy to understand: 

0-5 indicates severe sleepiness

5-10 indicates sleepiness is troublesome

10-15 indicates sleepiness is manageable

15-20 indicates that sleepiness is not much of a problem

 Excessive daytime sleepiness can cause a multitude of problems, especially during a work or school day when you should be alert.  The MSLT is usually recommended if hypersomnia or narcolepsy are suspected.  In these cases, the person can fall asleep even in the loudest or brightest of environments.  The typical procedure of the test, which takes approximately seven hours to complete, is reviewed with the individual beforehand.  The most important preparation is that they must avoid all caffeine and stimulants before the start of the study.

Generally, the multiple latency sleep test is performed after an overnight sleep study.  The first nap of the study is done 1.5 to 3 hours after you wake up from this study and about an hour after a light breakfast.  After the sensors are placed and connected to the computer, you are asked to lie still in the dark, quiet room and attempt to fall asleep.  The sensors will indicate to the technologist whether or not you have entered the REM (rapid eye movement) stage of sleep.

sleep study data

It will take approximately one to two weeks to get the results of the study.

The results are read by a sleep specialist, a neurologist, or a clinical neurophysiologist and are sent to the ordering physician (generally, the primary care physician).

How much does an MSLT cost?

The price of an MSLT varies from sleep center to sleep center. Hospital-based tests generally cost more than free-standing, non-hospital sleep center tests.  The price for an MSLT can range from $600 – $2200.



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