Multiple Sleep Latency Test (MSLT) - Overview and Facts
Excessive daytime sleepiness occurs when you are tired when you should be awake and alert. A board-certified sleep medicine physician will recommend an MSLT if he or she suspects you have excessive daytime sleepiness.
The multiple sleep latency test (MSLT) tests for excessive daytime sleepiness by measuring how quickly you fall asleep in a quiet environment during the day. Also knowns as a daytime nap study, the MSLT is the standard tool used to diagnose narcolepsy and idiopathic hypersomnia.
Preparing for the MSLT
A variety of factors can affect the results of your MSLT. These include:
- Drugs and medications
- Amount of sleep prior to sleep study
For this reason, the board certified sleep physician may recommend the following before your MSLT:
- Keep a sleep diary for two weeks. This will allow the doctor to see your sleep-wake patterns. This may help the physician identify other factors that may be causing daytime sleepiness. It will also help to ensure that you are allowing an adequate amount of time for sleep.
- Discuss the use of stimulants including caffeine with your sleep physician prior to your MSLT. If you are on any medications, your board-certified sleep physician will help you determine when you can use your medications before the MSLT. These substances can alter the results of your MSLT.
- The night before your MSLT you will have an overnight sleep study. For the MSLT to be accurate, you will need to sleep at least six hours during the overnight sleep study. An overnight sleep study will be used to determine if another sleep disorder such as obstructive sleep apnea is causing your excessive daytime sleepiness.
- You may be required to take a drug test the morning of the MSLT. The drug test is to ensure that your MSLT will be accurate. There are a number of drugs that can affect the results of your sleep study. The results of the drug test will be kept private between you and the physician.
Once you have finished these steps, you will be prepared for the MSLT.
The MSLT will last most of the day. Over the course of the day, you will take five scheduled naps. Each of these nap trials is separated by a two-hour break. Depending on the results, a shorter four-nap study may also be used. Be prepared to stay for the full five-nap version of the study.
- You will take your first scheduled nap an hour-and-a-half to three hours after you wake up from the overnight sleep study. About an hour before your first nap trial, you will eat a light breakfast.
- A sleep technologist will gently place sensors on your head, face and chin. These sensors are connected to a computer. Each is long enough so you can move around and turn over in bed. The sensors show when you are asleep and awake, and transmit data used to determine when you are in REM sleep. Once you are connected the technologist will test the sensors by asking you to move your eyes, clench your teeth and turn your head. A low-light video camera will allow the technologist to observe your MSLT from a nearby room.
- The nap trial begins when the lights are turned off. You will lie quietly in bed and try to go to sleep. The MSLT will measure how long it takes you to fall asleep. It will also measure how long it takes for you to reach REM sleep.
- The technologist will awaken you after you have slept for 15 minutes. If you are unable to fall asleep, the nap trial will end after 20 minutes. At this time you will have approximately a two-hour break. You will need to stay awake, and you are free to keep busy in whichever way you choose.
- This process will repeat four more times. After your second (noon) trial, you will have a light lunch. After your final nap trial, you will test the sensors again and they will be removed. You are free to leave when the final trial is complete.