Narcolepsy is a neurological sleep disorder that impacts the brain’s ability to properly regulate the body’s sleep-wake cycles. While there are different types of narcolepsy, the most common symptom of the disorder is excessive daytime sleepiness. EDS, which is necessary for a diagnosis of narcolepsy, causes one to struggle to stay awake during the day despite getting adequate rest.
These symptoms can make it difficult to function on a daily basis. Finding the most effective treatment for your narcolepsy starts with receiving the proper diagnosis. If your doctor suspects you have narcolepsy-related EDS, they may recommend a test used to diagnose EDS in particular: the multiple sleep latency test (MSLT).
Also known as the daytime nap study, the MSLT measures the time it takes you to fall asleep (known as sleep latency) in a quiet environment during the day. The MSLT is a full-day test made up of four or five scheduled daytime naps. Each nap, which lasts for 20 minutes or more, is separated by a two-hour break. During these naps, the sleep specialist conducting the MSLT will measure how long it takes for you to fall asleep, as well as how quickly you enter rapid eye movement or REM sleep.
Getting ready for an MSLT doesn’t need to be an anxiety-inducing experience. While undergoing a medical examination may seem daunting, this test is quick, noninvasive, and painless. In fact, many people who participate in sleep studies like the MSLT find learning more about their sleep habits to be fascinating.
You’ll likely have an overnight sleep study (called a polysomnogram or PSG test) the night before your MSLT. This test can help determine whether your excessive daytime sleepiness is caused by another sleep disorder, such as obstructive sleep apnea. To obtain accurate results from your MSLT, you’ll need to get at least six hours of sleep during the PSG test.
On the morning of your MSLT, you may be required to take a drug test. This is done to ensure your MSLT results will be accurate, as certain drugs can impact the outcome of a sleep test. Results are confidential.
The MSLT lasts for most of the day. You will take four or five scheduled naps throughout the test (depending on your results), each separated by a two-hour break. You’ll be able to eat a light breakfast roughly one hour before your first nap, which will be scheduled one-and-a-half to three hours after you wake up from the overnight PSG study.
During each nap, a sleep technologist will gently place sensors on your face, head, and chin. These sensors, which monitor when you are awake, asleep, and in REM sleep, are painless and long enough to allow you to move around in bed. Once these sensors have been placed on you, the technologist will test them by asking you to turn your head, move your eyes, and clench your teeth.
As with the PSG test, nap trials take place in a dark, quiet room. After the lights have been turned off, you will lie in bed and try to fall asleep for 20 minutes. The sleep technologist will observe you from a low-light video camera placed in the room while the MSLT sensors measure how long it takes for you to fall asleep and reach REM sleep.
If you fall asleep, the technologist will wake you up after 15 minutes. The nap trial will end after 20 minutes if you are unable to go to sleep. After this first trial, you’ll take a two-hour break, during which you’ll need to stay awake.
This process will repeat three or four more times, with a light lunch after your second trial (around noon). The sensors will remain on you until your final trial is complete. You’re free to leave once the sensors have been tested and removed.
Your doctor may ask you to keep a sleep diary for roughly two weeks before your MSLT. This will help your doctor assess your sleep-wake patterns and determine whether any other factors may be causing your EDS. Before your MSLT, be sure to let your doctor know if you use any stimulants (including caffeine).
A number of factors can affect the results of an MSLT, including:
Because an overnight sleep study is usually conducted the night before an MSLT, you’ll likely be asked to bring your usual overnight supplies (such as a toothbrush, toothpaste, and pajamas). In some cases, you’ll also bring food to eat. It may also be a good idea to bring items that will keep you entertained during the two-hour breaks between your scheduled naps, such as a book or tablet.
It will take about two weeks for your doctors to review the results of your multiple sleep latency test before you receive them. A sleep technologist will analyze your results first. They will chart the times you fell asleep during each nap and determine if and when you reached REM sleep.
These factors can be used to assess your condition. People with narcolepsy usually enter REM sleep two or more times during an MSLT, while people with other types of excessive daytime sleepiness fall asleep quickly (but don’t reach REM sleep).
A sleep specialist will interpret the results of your MSLT. They can use this information to diagnose you with narcolepsy or other disorders of excessive daytime sleepiness.
Following their diagnosis, your doctor will contact you and discuss the next possible steps in your treatment plan. If another doctor (such as your primary care physician) ordered the MSLT, the sleep doctor will send the test results to them as well.
Other tests used to diagnose narcolepsy can help sleep specialists determine the underlying cause of your symptoms.
A polysomnogram test is usually performed the night before the multiple sleep latency test. This overnight test monitors your breathing, eye movements, brain waves, and muscle tone to evaluate the quality and duration of your nighttime sleep. This helps your sleep specialist determine if and when your sleep patterns are disrupted.
During a PSG, you stay overnight in a sleep center in a dark, quiet, comfortable room. Along with a low-light video camera and two-way audio system, the technologists conducting the PSG test will monitor your sleep using sensors placed on your scalp, temples, chest, and legs. As with the MSLT, you’ll be advised against napping or consuming alcohol or caffeine (which can interfere with your sleep patterns) before your PSG test.
The maintenance of wakefulness test is another test used to evaluate excessive daytime sleepiness. Like the MSLT, this test is repeated several times between two-hour intervals — during which you aren’t permitted to sleep.
This test usually does not require you to have an overnight PSG test the night before the study, but you are encouraged to get a good amount of sleep. During a maintenance of wakefulness test, you are asked to remain awake for 40 minutes while sitting or lying down comfortably in a room with lowered light and sound. Any sleep during the MWT is considered abnormal and indicative of EDS.
While an estimated 135,000 to 200,000 people in the United States are living with narcolepsy, it’s believed that even more have the disorder but are undiagnosed. The MSLT is a valuable tool in the diagnosis of narcolepsy and excessive daytime sleepiness, and one of the first steps toward finding the best treatment plan for your symptoms.
Have you had a multiple sleep latency test? If so, share your experiences in the comments below. Or, if you’d like, start a conversation on MyNarcolepsyTeam.