The Multiple Sleep Latency Test (MSLT) is an objective test of physiologic sleepiness that was first employed at Stanford University and has since achieved widespread usage in clinical practice, both because of its intuitive approach to testing sleepiness and its multiple opportunities to test for sleep-onset rapid eye movement sleep periods (SOREMPs), which is useful in the diagnosis of narcolepsy. The American Academy of Sleep Medicine (AASM) has published a report indicating that the MSLT is considered to be the de facto standard for the objective measurement of sleepiness. The MSLT is indicated to rule out:
- Sleep Apnea
- Movement Disorders
- Circadian Rhythm Disorders
- Insufficient/Poor Sleep
- Other sleep disorders
The MSLT technique is standardized. Testing conditions require well-controlled, consistent procedures. Ideally, patients should discontinue therapy with any medication that might affect sleep latency (eg, stimulants, hypnotics, and antihistamines) and rapid eye movement (REM) latency (eg, antidepressants) for at least 15 days before the study. Therapy with such medications should be stopped for at least five half-lives of the drug and the longer acting metabolite. Urine drug screening is performed on the morning of the test to assist in confirming that the pretest conditions are met. Smoking should be stopped at least 30 min before each nap opportunity, and caffeine should be avoided on the test day, although acute withdrawal from caffeine may affect the test results. Vigorous physical activity and bright sunlight should also be avoided.
A polysomnogram should be performed the night before the MSLT to assess nighttime sleep quality and quantity. Untreated obstructive sleep apnea (OSA) or other causes of disrupted sleep should be ruled out or treated before proceeding with the MSLT. If the subject has known OSA, adequate nocturnal positive airway pressure therapy must be administered leading up to the MSLT in order to ensure that untreated OSA does not confound MSLT results. If the patient has a high number of periodic limb movements with arousals observed on overnight observation, the decision to proceed with the MSLT study must be based on clinical judgment. In addition, a minimum of 6 h of nocturnal sleep should be achieved before proceeding with the MSLT when evaluating for narcolepsy, since the use of this test to support a diagnosis of narcolepsy is “suspect” without a prior night of sleep of at least 6 h duration. The 6-h minimum total sleep time over the preceding night is advised whenever the test is performed.
Since MSLT results may be influenced by sleep up to 7 nights before the test, the preceding sleep-wake cycle should be standardized for at least 7 days, and patients should be advised to obtain adequate sleep for 1 to 2 weeks prior to test performance. They may be asked to complete sleep diaries for 1 or 2 weeks prior to testing. Actigraphy has also been suggested as an objective means to document adequate sleep leading up to the study.
On the day of the test, a light breakfast is recommended 1 h before the first trial, and a light lunch is recommended immediately after the second noon trial. The MSLT typically consists of five nap opportunities performed at 2-h intervals; four naps may also be used, but this may limit its usefulness in the diagnosis of narcolepsy. Naps are conducted in a sleep-promoting environment, typically a dark, quiet room that is maintained at a comfortable temperature. The initial nap begins 1.5 to 3 h after awakening from nocturnal sleep. Prior to the start of the nap, the subject should be asked whether they need to go to the bathroom or whether other adjustments are needed for comfort. Subjects should be in bed 5 min before the scheduled start of the test to perform calibrations of recorded parameters. In addition, this step is helpful in standardizing activity before the start of the test, which may influence nap latency. For each nap, the subject is instructed to “please lie quietly, assume a comfortable position, keep your eyes closed, and try to fall asleep.” The start of the test is signaled by turning off the bedroom lights. The test is ended 20 min later if no sleep has occurred or 15 min of “clock time” (not sleep time) after the first epoch of sleep, irrespective of whether REM sleep has occurred or not. Although positive airway pressure therapy is typically not used during the MSLT study itself in those patients with OSA, this matter has not been addressed in the guidelines and clinical judgment is recommended.