Multiple Sleep Latency Test
The Multiple Sleep Latency Test (MSLT) is a nap study. It is used to see
how quickly you fall asleep in quiet situations during the day. The MSLT
is the standard way to measure your level of daytime sleepiness. Excessive
sleepiness is when you are sleepy at a time and place when you should
be awake and alert. It affects about 5% of the general population.
The study is based on the idea that you should fall asleep in a shorter
amount of time as your feeling of sleepiness increases. The MSLT charts
your brain waves and heartbeat and records your eye and chin movements.
The study also measures how quickly and how often you enter the rapid-eye-movement
(REM) stage of sleep. Results of the nap study are routinely used to detect
The study isolates you from outside factors that can affect your ability
to fall asleep. These factors include such things as the following:
• Temperature (too hot or too cold)
Other factors that can still affect the results of the study include the
• Drugs and medications
• Amount of sleep prior to the study
The use of stimulants needs to be stopped for two weeks before the MSLT.
Your sleep specialist should help you properly schedule the use of any
Who gets it?
The MSLT is the standard tool used to evaluate people who are thought
to have narcolepsy. Most people with narcolepsy fall asleep in an average
of less than five minutes during the MSLT nap trials. Some take longer
than five minutes to fall asleep. There are also people without narcolepsy
who fall asleep in less than five minutes.
The MSLT also counts sleep-onset REM periods (SOREMPS). This is when you
enter REM sleep very soon after you fall asleep. REM sleep is normally
the fifth and last stage of each sleep cycle. It usually begins about
90 minutes after you fall asleep. People with narcolepsy often have two
or more SOREMPS in a nap trial.
The MSLT may be used to see if a person has idiopathic hypersomnia. Patients
with idiopathic hypersomnia fall asleep easily but do not have SOREMPS.
The MSLT reveals a broad range of time in which it takes normal sleepers
to fall asleep during the study. Normal sleepers tend to fall asleep in
an average of about ten minutes or more during the five naps of the MSLT.
Due to the wide range of normal times, the results from these nap trials
alone are not enough to diagnose a sleep disorder. Doctors must also consider
other data, tests, and medical information.
What happens when I have it?
You may be asked to take a test to screen for drugs before the nap study.
This will normally take place on the morning of the MSLT. It will help
show that the nap study results are accurate. It will be helpful if you
fill out a sleep diary for at least one week before the MSLT. This will
allow the doctor to see your normal sleep-wake pattern. Smoking should
be stopped at least 30 minutes before each nap trial.
You will not be allowed to have any drinks with caffeine during the study.
You will also not be able to see any bright sunlight. Outside factors
that might affect your sleep are limited. Your room is made dark and quiet.
The room temperature is set at your personal comfort level. The daytime
nap study is taken right after you do an overnight sleep study. For the
MSLT to be accurate, you should have had a total sleep time of at least
six hours during the overnight sleep study.
The MSLT consists of five nap opportunities with breaks lasting for two
hours in between them. A shorter four-nap study may also be used. But
the five-nap version is more reliable for detecting narcolepsy. The first
nap trial begins between 1.5 and three hours after you wake up from the
overnight sleep study. You will be given a light breakfast at least one
hour before the first nap trial.
Sensors are placed on your head, face, and chin. They send tiny electrical
signals to a computer. The signals show when you are asleep and awake
during the study. The brain-wave and eye-movement detectors show when
you are in REM sleep. This is a stage of sleep where your eyes twitch
and your brain waves are very active.
You will not feel any pain during the MSLT. The sensors are gently taped
to your skin and connected to a computer. The cables are long enough to
let you move around and turn over in bed. You will be asked to move your
eyes, clench your teeth and turn your head. This will make sure that the
sensors are working. A low-light video camera allows a technologist to
see you from a nearby room.
For each nap trial, you are asked to lie quietly in bed and try to go
to sleep. Then the lights are turned off. Once the lights are out, the
test will measure how long it takes you to fall asleep. Your vital signs
will continue to be measured as you sleep.
After sleeping for 15 minutes, you will be awakened. Each trial will end
if you do not fall asleep within 20 minutes. Between nap trials, you will
have to stay out of bed and occupy yourself so that you remain awake.
A light lunch should be provided right after the end of the second (noon) trial.
After the last nap trial, you will test the sensors again, and then they
will be removed. This will complete the study, and you will be free to go.
Who reads it?
A technologist is the first one to look over the data from a nap study.
First, he or she will chart your wake-sleep times and sleep stages. He
or she will be sure to look for and count any times you entered REM sleep.
The results will be given to a doctor. The MSLT is not a test that you
can fail. The doctor will simply review the study to find out what kind
of sleep problem you may have. The results of a nap study are always reviewed
by a board-certified sleep specialist.
How do I get the results?
It usually takes about two weeks to get the results of a nap study. At
times the doctor who takes a look at the study needs to get more information.
He or she may talk to the technologist or to the doctor who sent you to
The doctor who ordered the MSLT will discuss the results with you. If
your primary care doctor ordered it, then the results are sent to him
or her. If you met with a doctor in the sleep center, then he or she will
tell you the results.