What is a Multiple Sleep Latency Test?

A MSLT is a diagnostic test used to determine sleep disorders in which excessive daytime sleepiness is the primary complaint.

It is always a follow-up test to the overnight PSG which is used to rule out other sleep disorders such as sleep apnea, restless leg syndrome, parasomnias, and others.

The most common sleep disorders that MSLTs diagnose are narcolepsy and idiopathic hypersomnia. A MSLT is also useful in differentiating between the two sleep disorders as their symptoms are very similar in nature.

How is the test Conducted?

Shortly after having a PSG, patients come in during the daytime for their sleep test during which they are given 5 scheduled naps each 20 minutes long and separated by 2 hours apart. The purpose of the tests are to determine how likely and quickly a patient falls asleep during the day in a relaxed and quiet environment.

During these nap periods, patients are in a dark, quiet, comfortable atmosphere devoid of any distractions, stimulations, or environmental factors that may prevent them from sleeping.

Patients are hooked up to the same monitoring equipment during their nap times as they are during an overnight PSG. The equipment is composed of electrodes and monitors that collect a variety of data including:

• Wires with small cup electrodes attached to your scalp with a conductive paste to measure brain activity. This lets the tech know if you are sleeping, and what stage of sleep you are in.
• Wire electrodes that are taped to your face near the eyes and chin to show muscle activity. These electrodes are used to measure eye movements, which also give clues to sleep stages, as well as chin movements which can observe possible nocturnal teeth grinding as well as other sleep disorders related to muscle activity.
• 2 elastic belts around your chest and stomach to measure breathing effort.
• A nasal cannula (clear plastic tubing) and small heat monitor to measure all breathing activity.
• A wire electrode on each leg to measure body movement/muscle activity.
• A monitor taped to your finger to detect oxygen levels during the study.
• 2-3 lead EKG monitors to show heart rate and rhythm.
• A small  mic applied to your throat to detect snoring.

A registered polysomnographic technologist (RPSGT) will monitor and record the data in an adjacent room and will wake the patient up at the 20 minute mark that concludes each nap period.

What does it measure?

The idea behind the multiple sleep latency test is that sleepy people are more likely fall asleep faster than others, especially when a sleep disorder is the root cause of the problem.

The main function of the test is to determine sleep latency (the time it takes to transition from wakefulness to sleep) and sleep onset REM periods (how quickly the patient enters REM sleep).

In most people, sleep latency takes approximately 5-15 minutes to pass from wakefulness into the first stages of sleep. For patients with idiopathic hypersomnia (IH) and narcolepsy, sleep latency occurs much more quickly. Patients with IH usually have a sleep latency of 8 minutes or less, and patients with narcolepsy have a sleep latency of 5 minutes or less.

For normal sleepers, the first cycle of REM sleep occurs around 70-90 minutes after sleep begins. The same is true for those with idiopathic hypersomnia. However, one of the most telling differences between narcolepsy and IH is that those suffering from narcolepsy experience very quick sleep onset REM periods at under 15 minutes.

In the absence of cataplexy (a very common symptom of narcolepsy type 1) a multiple sleep latency test is often the best way to differentiate between narcolepsy and idiopathic hypersomnia.

Based on the findings of the sleep test, a sleep specialist or the patient’s primary care provider can determine the best course of treatment for the sleep disorder.

If you are suffering from excessive daytime sleepiness and believe that you may have narcolepsy, idiopathic hypersomnia, or any other sleep disorder, discuss your symptoms with your primary care physician.

If you live in Alaska and are ready to have a sleep study to get to the root of your sleep troubles, contact The Alaska Sleep Clinic to receive a free 10-minute phone call with one of our sleep educators who can quickly determine if a sleep study is right for you.