The multiple sleep latency test is a diagnostic apparatus test in sleep medicine, it is used especially for sleep disorders, sleep onset and sleep through disorders, and narcolepsy diagnosis.
What is the multiple sleep latency test?
If patients present to the doctor suffering from increased daytime sleepiness, then in addition to polysomnography in the so-called sleep laboratory, the multiple sleep latency test is also used to clarify the cause. The multiple sleep latency test is a development of American sleep researchers and is therefore originally also called multiple sleep latency test, in the German language use the English designation could not become generally accepted however. The first clinical use of the multiple sleep latency test was in 1976, when it was used to investigate a tendency to increased daytime sleepiness. Soon, so-called sleep onset periods of REM sleep could be detected, which are still significant in narcolepsy diagnostics today. MSLT is the most important sleep medicine test for the reliable detection of narcolepsy. In sleep medicine, the multiple sleep latency test is also abbreviated MSLT. If patients present to the doctor suffering from increased daytime sleepiness, the multiple sleep latency test is used to clarify the cause in addition to polysomnography in the so-called sleep laboratory. In particular, narcolepsy, which can lead to spontaneous deep sleep even during the day, is typically associated with prematurely occurring REM periods. These can be visualized in the graphic evaluation using the multiple sleep latency test to confirm the diagnosis.
Function, effect, and goals
In sleep medicine, the multiple sleep latency test is usually performed in parallel with polysomnography. For this purpose, the patient is called into a sleep laboratory in the evening, connected to measuring devices via multiple electrodes, and then asked to fall asleep as if he or she were in his or her own bed. The electrosensors can record whether, when and how deeply a subject falls asleep when the test is performed. MSLT consists of multiple rounds. Unlike ambulatory polysomnography, the multiple sleep latency test does not have a portable recording device that the patient can take home. Thus, MSLT must necessarily be performed in a sleep laboratory. Most sleep laboratories in German hospitals are affiliated with internal medicine departments. The German Society for Sleep Medicine recommends five runs in a 2-hour interval, these measurement intervals begin about three hours after the nocturnal polysomnography, which is thus usually preceded by a multiple sleep latency test. In order to be able to reliably assess the sleep-wake rhythm of a test person, it is necessary to keep a so-called sleep diary. In the detailed version of the MSLT, a continuous sleep period of six hours should precede the actual test performance. The shortened test version will only be meaningful if at least two shortened REM sleep periods, SOREM, had already occurred in it. Before performing the test, all stimulant or sedative medications must be discontinued in order to obtain an unbiased result. Food intake or caffeine consumption can also falsify the test values. On the day of the test, heavy physical work should be avoided, as should too long exposure to the sun. The MSLT includes EEG, EOG, EMG and ECG as a full test. Thus, the brain waves are measured, the twitching movements of the eyelids during REM sleep, the reaction of the skeletal muscles as well as the excitation conduction of the heart. After the patient has assumed a comfortable position, he is asked to fall asleep. If this is successful, the patient is woken up again after the measurement and asked to leave the bed in order to be prevented from sleeping until the next run. The evaluation includes in particular the analysis of REM sleep behavior, as well as fall asleep latency and sleep stages. If the patient cannot fall asleep, then a measurement cycle ends after 20 minutes. A visual image, the so-called hypnogram, is created from all measurement parameters of the MSLT. The clinical assessment of daytime sleepiness in narcolepsy will never be based on the results of the MSLT alone, but also on certain blood values, physical examinations and medical history.
Risks, side effects and dangers
The correct performance of the MSLT depends on the general conditions in the sleep laboratory and on the preanalytics, whereby the test-compliant behavior of the patient is of particular importance. The German Society for Sleep Medicine has published guidelines for the correct performance of the test, but not every sleep laboratory adheres to them, so that there may well be variations in the test performance. The performance of the MSLT is considered to be particularly personnel-intensive, because the patient must be constantly observed before, during and also after the test. Only medical and non-medical personnel with sufficient experience in sleep medicine should be entrusted with the performance of the MSLT. If the measurement deviations are too large, the test can also be repeated, which has already become standard practice at some sleep centers, in order to exclude as many sources of error as possible. Especially the test results after a first night in the sleep laboratory are often not usable, sleep physicians also speak of the first night phenomenon. The MSLT differs from the so-called multiple wakefulness test mainly in the lying posture, the room brightness and in the request to stay awake instead of falling asleep. In order to obtain truly valid test results, standardized test conditions must be adhered to according to the specifications of the German Society for Sleep Medicine. Adherence to the test specifications should be worked through and documented using a list for each patient. The sleeping room itself is also important. It should be possible to darken it completely, without any residual light simply from open curtains or streetlight illumination. Absolute quiet in the sleeping room is also imperative. Since this cannot always be guaranteed, earplugs can also be used to eliminate residual noise. Also of high importance for valid results is an optimal temperature control of the sleeping room.
