Multiple Sleep Latency Test
A multiple sleep latency test (MSLT) is a daytime sleep study used to diagnose possible sleep disorders in individuals who experience excessive sleepiness during the day. This test usually begins about two hours after the patient awakens. Electrodes are attached to the patient's head, and over the course of a 5 to 30 minute period, the patient will lie in a quiet, darkened room. A technician will record whether the patient falls asleep and, if so, how long the process takes. During this nap period, the patient is not only monitored for brain activity, but also for heart rhythm, respiration, oxygen levels, muscle tone and movement of eyes and extremities.
The stages and duration of sleep are carefully monitored as well. This procedure is typically repeated five times during the day to allow for differences in body rhythms. The sleep periods are approximately two hours apart and the patient must remain awake during these intervals.
The multiple sleep latency test can determine not only whether the patient actually does sleep during the day, but whether or not the patient is experiencing rapid eye movement (REM) sleep. Determining the type of sleep being experienced is a diagnostic tool in differentiating the two sleep disorders involving daytime sleepiness: narcolepsy and idiopathic hypersomnia.
Both sleep disorders occur in spite of sufficient nighttime sleep and neither is caused by prescription medication or substance abuse. Narcolepsy is characterized by inability to stay awake during the day. Patients with narcolepsy may fall asleep inappropriately and sometimes dangerously -- while having a conversation, while eating, or even while driving. Idiopathic hypersomnia is characterized by excessive sleepiness during the day with no identifiable cause.