Multiple Sleep Latency Test

The Multiple Sleep Latency Test (MSLT) is a sleep disorder diagnostic tool. It is used to measure the time elapsed from the start of a daytime nap period to the first signs of sleep, called sleep latency. The test is based on the idea that the sleepier people are, the faster they will fall asleep.

The MSLT is used extensively to test for narcolepsy, to distinguish between physical tiredness and true excessive daytime sleepiness, or to assess whether treatments for breathing disorders are working. Its main purpose is to discover how readily a person will fall asleep in a conducive setting, how consistent or variable this is, and the way they fall asleep in terms of REM sleep and other brain patterns. This can be used to identify and differentiate between various sleep problems.

The test consists of four or five 20-minute nap opportunities set two hours apart, often following an overnight sleep study. During the test, data such as the patient's brain waves, EEG, muscle activity, and eye movements are monitored and recorded. The entire test normally takes about 7 hours during the course of a day.

History
The Multiple Sleep Latency Test was created in 1977 by sleep pioneers William C. Dement and Mary Carskadon. It developed out of repeating a project done in 1970 by Dr. Dement called the 90-minute day. They informally called the 0–5 minute range the twilight zone due to its indication of extreme physical and mental impairment.

Typical procedure
Preparation: On the day of the test the patient is asked not to consume any stimulants, such as tea, coffee, colas, and chocolate.
 * Often a formal sleep study has been performed the night before.
 * Sometimes urine screening is done to make sure no substances exist in the subject's body that might interfere with sleep.
 * The patient may be asked to fill out a pre-test questionnaire.
 * Electrodes are attached to the patient's head to record brain waves.
 * Electrodes are attached by the eyes to record eye movement.
 * Electrodes are attached to the chin to detect muscle tone.
 * Heart beat may also be monitored.
 * The patient is asked to perform simple tasks to test that the equipment is working properly.
 * The patient is asked to nap for 20 minutes, and then is awakened.
 * The nap process is repeated every 2 hours for a total of four or five times.
 * The patient may be asked to fill out a post-test questionnaire.

A clinical neurophysiologist, neurologist or sleep specialist will review the results and inform the patient or the patient's primary care physician of the interpretation of the test result in the context of the clinical problem.