In addition to overnight studies that are conducted in the sleep clinic or at home, there are two other diagnostic tests that are conducted during the daytime at the sleep clinic: Multiple Sleep Latency Test (MSLT) and Maintenance of Wakefulness Test (MWT).
Patients who experience excessive daytime sleepiness or who fall asleep at inappropriate times may be candidates for a MSLT or MWT. The MSLT is designed to measure how long it takes a person to fall asleep during the course of a day. The MWT tests a person’s ability to resist sleep and stay awake for a designated period of time. During these studies, the sleep technologist monitors the patient’s sleep/wake patterns. The MSLT and MWT are used to diagnose narcolepsy or idiopathic hypersomnolence.
The MSLT begins two hours after awakening from a diagnostic polysomnography; it consists of four to five attempts at napping scheduled 2 hours apart. Whereas some of the sensors used in the previous overnight polysomnography are removed, others are retained to record sleep latency (the number of minutes required to fall asleep). During testing, the patient is asked to relax and try to fall asleep. The test measures how quickly the person falls asleep during regular waking hours as well as the kind of sleep experienced during the naps.
Like the multiple sleep latency test, the maintenance of wakefulness test provides an objective measurement of the degree of daytime sleepiness. However, instead of measuring the patient’s ability to fall asleep, the MWT measures the patient’s ability to stay awake for a defined period of time under sleep-inducing circumstances. The MWT may be done following an overnight polysomnography, but it doesn’t necessarily have to follow polysomnography. The test usually begins two hours after awakening and involves a series of 5 naps conducted at 2-hour intervals throughout the day. The test measures the person’s ability to resist sleep and stay awake when instructed to remain awake for 20 minutes.
The MWT is based on the idea that, in some cases, the patient’s ability to stay awake may be more important than his or her ability to fall asleep. The test is generally used to determine whether an individual’s inability to stay awake is a public or personal safety concern. It is also commonly used to document treatment of a sleep-related disorder for the Department of Motor Vehicles or for an employer.