Multiple sleep latency Test (MSLT) and Maintenance of Wakefulness Test (MWT) by Murtaza Syed
Multiple Sleep Latency Test (MSLT) &
MAINTENANCE OF WAKEFULNESS TEST
Syed Irshad Murtaza
Multiple Sleep Latency Test
(MSLT) latency test)
MSLT (Multiple sleep
examination to test reasons for fatigue during the
daytime or a compulsive tendency to fall asleep.
It is a series of recordings to monitor a person's
MSLT is a nap study which is used to see how quickly
a person falls asleep in quiet situations during the
It is the standard way to measure the level of daytime
sleepiness & is helpful to rule out the other differential
diagnosis of other pathological abnormalities.
• It also measures how quickly and how often a
person enters the REM stage of sleep
• It can be used to test for narcolepsy (sudden
and uncontrollable onsets of sleep) .
• To distinguish between physical tiredness and
true excessive daytime sleepiness.
• Its main purpose is to serve as an objective
measurement of sleepiness.
What is Narcolepsy ?
• Narcolepsy is a neurological condition affecting
the area of the brain that controls waking and
Narcolepsy is characterized by sudden &
uncontrollable attacks of sleep at irregular &
unexpected times. Its main features are as
• Excessive daytime sleepiness (EDS)
• Hypnagogic/Hypnoponpic hallucinations.
• Sleep paralysis
The cells that produce the small peptides, HO, reside in the hypothalamus, an
area deep in the brain. Recent rodent studies indicate that these cells
connect to brain regions that are involved in sleep and wakefulness,
including the locus coeruleus, raphe nuclei, tuberomammillary nucleus and
pontine reticular formation, among others. This evidence suggests that,
normally, HO helps the sleep and wakefulness areas carry out their jobs.
And HO-related abnormalities may impair their function
MSLT Findings in Narcolepsy
•Normally sleep latency should at least be ≥8 min. Latency
prior to this period after lights out is to be considered as
early sleep latency in adults, which is regardless to prior
disturbed sleep, fatigability, jet lag, shift duty, drugs etc.
Mean sleep latency, which is calculated with all the onset
latencies of the sequential naps to obtain.
• To calculate for the Mean Sleep Latency, one would add
up all of the Sleep Latencies then divide by the number
• Sleep onset REM period (SOREMP) of ≥ 2 nap
which is obtained within ≤ 20 minutes of the sleep time is
considerable for the diagnosis of narcolepsy.
How to perform MSLT
• The MSLT is a series of 5 naps taken at 2 hour
intervals, starting at approximately 8-9:00 A.M.
• This is done the following day after a
polysomnogram (PSG) (with normal findings)
where a recording of the electrical activity of
many physical variables that occur during sleep.
• There are very rare cases reported to be having
the presence of obstructive sleep apnea and
narcolepsy simultaneously in the same subject.
Recommendations for MSLT
• The first nap trial should be started between
1.5-03 hours after waking up from the
• For the MSLT to be accurate, subject should
have had a total sleep time of at least six
hours during the overnight sleep study.
• The MSLT determines how long it takes a
person to fall asleep at preset times
throughout the day.
• Four or five segments are to be recorded.
• The patient is put to sleep at 2 hours interval of
• Each segments is allowed to last 20 minutes if
there is no sleep recorded, or a maximum of 15
minutes after the first epoch of sleep.
• It is recommended to record the sleep with
continuity for 20 minutes. The time starts from
the first drowsy if subject gets asleep,
otherwise to be scored from light off, if doesn’t
MSLT and its findings.
• The MSLT also counts sleep-onset REM periods
• This is when a person enters REM sleep very soon
after falling asleep.
• In normal individuals it usually begins about 90
minutes after falling 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 don’t have SOREMPS .
Calculation for Mean Sleep Latency
Add all of the sleep latencies
(including No Sleep of 20 minutes)
and divide by the number of naps
Nap #1: 6.0 minutes
Nap #2: 3.0 minutes
Nap #3: 0.0 minutes
Nap #4: 20.0 minutes
Nap #5: 2.5 minutes
31.5 minutes ÷ 5 = 6.3 minutes
Mean Sleep Latency = 6.3min
Objective of the Study
• The objective is to identify the latency of sleep or
time elapsed from lights out of the first epoch of
• This latency is defined as the point in the
polysomnogram (PSG) at which sleep occupies 50%
or more of the epoch.
• A 50% reduction of alpha activity along with slow
rolling eyes movements and a subtle reduction in
muscle tone indicate stage1.
• REM sleep latency is defined as the time from the
beginning of sleep to the onset of REM.
Diagnosis and Precautions
• To be diagnosed as Narcoleptic, the patient
would have to demonstrate a Mean Sleep
Latency (an average of all the sleep latencies) of 5
minutes or less and demonstrate at least 2 Sleep
Onset REM Periods (SOREMP).
The absence of sleep on a nap opportunity is
recorded as a sleep latency of 20 minutes
• Smoking should be stopped at least 30 minutes
before each nap trial.
Precautions prior to MSLT
• Patient will not be allowed to have any drinks
with caffeine during the study.
• Patient will also not be able to see any bright
• Vigorous physical activity should be avoided during the
• Any stimulating activities by the patient should end at
least 15 minutes prior to each nap opportunity.
• A light breakfast is recommended at least 1 hour prior to
the first trial, and a light lunch is recommended
immediately after the termination of the second noon
Interpretation (Case discussion)
This is MSLT preceded by Prolong PSG which is normal.
During this MSLT 5 naps were recorded at two hours
interval, each nap was terminated at 20 minutes. Onset
sleep latency during each nap was 30,30,30,90 and 120
seconds respectively. The mean sleep latency was 1
minute. During MSLT three Sleep onset REM periods
(SOREM) were noted. Sleep onset REM period latency of
each nap was 1, 3 & 4 minutes respectively. The mean
SOREM latency was 2.6 minutes.
Conclusion: (case discussion)
Severe abnormal MSLT study the findings are suggestive of
• The Maintenance of Wakefulness Test (MWT) is
an evaluation used as a quantitative
polysomnographic (PSG) measurement of
soporific (dreamy) circumstances. It shows
whether or not a subject is able to stay awake
for a defined period of time. This is an indicator
of how well one is able to function and remain
alert in quiet times of inactivity
Standardization of MWT
• The MWT is a series of nap studies during the
day in which the subject is asked to stay awake
and not fall asleep. How well they can perform
that task relates to their degree of daytime
• MWT- the Maintenance of wakefulness test is
some times used in place or in addition to the
MSLT as an assessment of daytime somnolence.
• It is a modification of the MSLT performed in a
similar manner, with recordings obtained at two
hour intervals following nighttime PSG.
Objective of MWT
The MWT is used to see how well a sleep
disorders patient is able to stay awake after
starting treatment. It is also used to help
judge whether a patient is too tired to drive or
perform other daily tasks.
This can show if treatment is helping a patient
Factors affecting the Study
• The test isolates you from outside factors that can influence the
ability to fall asleep. These factors include the following:
• Temperature (too hot or too cold)
• Other factors that can still affect the study include the following:
• Drugs and medications
• Amount of sleep prior to the study
• 4-trial MWT 20-minute (AASM Guidelines recommendation is 40 min)
protocol is recommended at 2hour intervals.
• First trial begins 1.5 to 3 hours after the patient’s usual
• Room should be maximally insulated from external light.
• Light source should be positioned slightly behind
• patient’s head (out of field of vision)
• Room temperature should be set based on the patient’s
• Patient should be seated in bed, with the back & head
supported by a bedrest/bolster pillow such that the neck
is not uncomfortably flexed or extended.
Procedure &Patient instructions
• The MWT varies from the MSLT in the recording
conditions and the instruction to the patient.
• The recording is performed with the patient
sitting in a chair in a dark room.
• The patient is instructed to sit quietly with eyes
open and remain awake during the recording to
assess an individual’s capability not be
overwhelmed by sleepiness- that’s is the
underlying functioning of the wakefulness
system is assessed
Instructions to patients
• ‘Please sit still and remain awake for as long
as possible. Look directly ahead of you, and do
not look directly at the light.’ Patients should
be disallowed from using extraordinary
measures such as slapping the face, pinching
• Trials are ended after 20 minutes if no sleep
occurs, or after unequivocal sleep.
• The first occurrence of sustained sleep is
defined as 3 consecutive 30 s epochs of stage
1 or any single 30 s epoch of another sleep
stage (II, III, IV, or REM).
• The MWT has proved useful in evaluating
treatment effects in patients with narcolepsy
and sleep related breathing disorders.
• MWT often reveals improvement in treated
patients who continue to physiological sleepy.
The major drawback in the use of Maintenance of
wakefulness test is that it has lack of normative
• AASM Practice Parameter: Practice Parameters for
• Clinical Use of the Multiple Sleep Latency Test and the
Maintenance of Wakefulness Test, Sleep, Vol. 28, No.
• Electroencephalography, Basic principles, clinical
applications, and Related fields, by Ernst Niedermeyer,
4TH Edi, vol 2 page 872-3
• Aldrich MS. Narcolepsy. N Engl J Med 1990;323:389-94.
• Thorpy MJ, Goswami M. Treatment of narcolepsy. In: