What is the Multiple Sleep Latency Test (MSLT)?

Posted by Darian Dozier on Dec 18, 2023 7:20:00 PM

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Excessive daytime sleepiness is characterized by the strong urge to go to sleep during activities in which you should be alert and awake. Have you experienced excessive daytime sleepiness? If so, then your physician might recommend that you undergo sleep-related testing. One of these tests might be the multiple sleep latency test, or MSLT. This can help you measure daytime sleepiness. We will discuss what MSLT can diagnose, who would take the test, preparing for it, with expectations for it, and understanding the results.

What is the Multiple Sleep Latency Test?

Doctors can use the MSLT to evaluate why someone might be experiencing excessive daytime sleepiness. It can also help undercover underlying sleep disorders. People undergo MSLT during daytime hours, which makes it different than the polysomnograph, a sleep test that happens at night. This normally happens the day after an overnight sleep study, meaning you'll spend about 24 hours in a sleep study facility carrying out these two tests. The MSLT measures how long it takes for you to fall asleep.

Sleep latency is the amount of time that it takes one to fall asleep after they lie down. The MSLT wants to see how long it takes a person to fall asleep, and what sleep stages they fall asleep into across multiple short naps throughout the day. Its characteristic that individuals progress through sleep stages going from stage 1 to stage 3 to REM sleep. If any of these sleep periods are out of order, the MSLT will be able to pick up on that.

What does the MSLT diagnose?

Sleep specialist primarily used the MSLT to diagnose disorders like narcolepsy and hypersomnia. These are two sleep disorders marked by excessive daytime sleepiness and occasional oversleeping. Excessive daytime sleepiness can also accompany insomnia, obstructive sleep apnea, periodic movement disorder, and circadian rhythm disorders.

Excessive daytime sleepiness can also be linked to neurological disorders like Parkinson's disease, epilepsy, multiple sclerosis. However, the MSLT is typically not used to diagnose any of these conditions. Just ones that involve conditions in which one may experience an overwhelming desire to fall asleep, and may fall asleep in the sleep stage other than stage one. These characteristics would be diagnostic of a sleep disorder like narcolepsy or hypersomnia.

Best person for an MSLT

The MSLT may be appropriate for people who are experiencing excessive daytime sleepiness due to a number of reasons. There is a distinction between excessive daytime sleepiness and fatigue. Excessive daytime sleepiness is the struggle to stay awake during times when one is supposed to be awake. This could include working, being in school, driving, and anything else that requires full attention. However, just feeling tired means that you could fall asleep if given the opportunity, but you're not actively falling asleep in that moment.

Before jumping to the MSLT, your doctor may start out with an Epworth Sleepiness Scale,  which asks you to rate how likely you are to fall asleep in eight different scenarios. That is a self-assessment that serves as a screening tool to identify if you actually struggle from excessive daytime sleepiness or just fatigue. Whatever your score is on this questionnaire will help determine if you need to take an MSLT.

Preparing for an MSLT

Whatever your lifestyle is weeks before the MSLT can affect the results. For example, the number of hours that you sleep at night, whether or not you take any drugs or medication to sleep, how active you are, and how quickly you fall asleep at night can help determine your results on the MSLT. This is the reason that doctors ask individuals to maintain a steady sleep routine in the weeks prior to the MSLT. If your doctor gives you instructions on what to do prior to the study, it's important that she follow them exactly to a tee.

One to two weeks before taking the MSLT, your doctor might ask you to start recording your sleep times and the sleep diary, or where a device called an actigraph to monitor your sleep wake activity. If you have to take certain medications or supplements they might ask you to stop taking them momentarily so that way your test results are not impacted by them.

Generally, and MSLT will take place the day after an overnight sleep study, or a polysomnography. The polysomnography is required to diagnose different sleep disorders, like obstructive sleep apnea, restless leg disorder, insomnia due to some secondary cause, etcetera. The next day, you will participate in the MSLT which will begin about two hours after the sleep study. Before starting the MSLT, you might be asked to take a urine drug screen and take a questionnaire about how well you slept in the sleep lab.

The actual MSLT involves a series of naps and breaks. People are given the opportunity to take four to five short naps, that are broken up by breaks of two hours. You can leave the sleep laboratory and get food during your breaks, but you must stay awake and avoid any caffeine. You should also avoid any stimulating activities that could interfere with the results of the study. This can include smoking and any vigorous exercise before each snap.

During the nap, you will lie down in the bed in the dark quiet room like you did during the sleep study. You are going to be monitored similarly as you were in the polysomnography, using sensors to measure any brain activity, eye movements, vital signs, etc. The technician will carry out all of the tests to make sure that the machines are working, and then they ask you to close your eyes and try to fall asleep. During both studies you can communicate with the technicians if you're having any concerns from need help with anything.

MSLT results

Understanding your results is important as the MSLT results can provide you information about your sleep latency, or the amount of time that it takes you to fall asleep after the technician turns the lights off. The results can contain measurements of your brain wave activities and eye movements, which allows technicians to figure out which sleep stage you are in during your naps.

If you fall asleep, you are allowed 15 minutes to see if you enter REM sleep. If you're still awake after 20 minutes, then the nap opportunity is stopped and technicians will record 20 minutes as the time that it took you to fall asleep. Normally, the REM stage first occurs after about 90 minutes of sleep.

REM sleep experienced shortly after falling asleep, means that you have sleep onset REM periods (SOREMP). Two of the primary criteria for narcolepsy include average sleep latency of less than about 8 minutes during an MSLT nap, and the occurrence of at least two SOREMPs during the nap periods.

Also, in order to receive a diagnosis of hypersomnia, the sleeper must have average sleep latency of less than 8 minutes. However, people with idiopathic hypersomnia will exhibit less than two SOREMPs during the MSLT and no more SOREMP 's if they were already quick to enter the REM sleep during the overnight sleep study.

Results of the MSLT need to be interpreted and explained by a professional. During your follow up appointments with your sleep health provider or specialist, you will learn your diagnosis and what the treatment plans are. If you think that you may struggle with narcolepsy or hypersomnia, then please click the orange button below to take a free online sleep test talk with one of our sleep health professionals to see if you need an MSLT.

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