Over the past decade, sleep research has skyrocketed thanks to many organizations who try their best to raise awareness about the importance of sleep.
Unfortunately, despite all effort, it seems that the quality of sleep keeps dropping and sleep disorders become more and more common. Based on the latest survey, over 35 percent of Americans do not get enough sleep; the average number of snoozing is 6.8h. Compared to 1985 there has been an increase of 31 percent when it comes to people who sleep less than six hours.
A fun fact is that a century ago (in 1910) people slept around 9h on average.
Times have changed since then, but we can all agree that the importance of proper rest and sleep hasn’t. That is why many doctors and sleep specialists have decided to develop tests that can help them define disorders and understand them better.
Multiple sleep latency test is one of them.
What is the Multiple Sleep Latency Test?
Multiple sleep latency test is a helpful tool that doctors use to determine a sleep disorder where daytime sleepiness is the leading cause of disrupted sleep. It usually follows Polysomnography or PSG, which is an overnight test that monitors the sleep stages and patterns. PSG test can also help exclude sleep disorders including restless leg syndrome, sleep apnea and others.
Some doctors decide to include tests like:
- CPAP titration testing which helps to determine adequate pressure for those who use CPAP machine
- Split Night Study that helps doctors define if the person is suffering from obstructive sleep apnea
- MWT or maintenance of wakefulness test that measures how awake and alerts a person is while being an environment that is free from stimulations.
How Does MSLT Work?
After conducting a PSG, MSLT is scheduled during the day, but the patient must stop consuming antidepressants and stimulants a few weeks before taking the test.
On the day of the MSLT, the patient will have five naps lasting 15-20 min each and 2h apart. The goal of this test is -to see how fast the person will fall asleep during the daytime in an environment that is relaxing and quiet.
This test also shows when the patient enters the stage of REM sleep. In most cases, people who do not have any disorder will not enter REM sleep while napping for a short time. The stage of REM sleep occurs after more than 1h during the night.
The nap takes place in an environment free from distractions, noise, and stimulations that can prevent them from falling asleep. For Multiple sleep latency test to work, a person must sleep at least 8h the night before, and should not be exposed to strong sunshine and exercise in the morning.
The equipment used for this type of test is similar to the one that is used for PSG. It consists of monitors and electrodes that collect data. Pieces of equipment include:
- Small cup wires attached to the scalp to measure brain activity
- Two elastic belts that go around your stomach and chest to regulate breathing
- Electrodes with wires attached on your face and chin to follow the activity of the muscles and eye movement. The reason why they are attached to your chin is to follow possible teeth grinding.
- Nasal Cannula and heat monitor
- A microphone small in size to detect possible snoring
- Monitor that follows your levels of oxygen attached to your fingers
- Electrodes attached to your legs to track muscle activity
- EKG to track the rhythm and heart rate
What Does MSLT Measure?
The primary function of this test is to determine the time people need to transit from awake to sleepy and how fast ones goes into REM sleep. The idea is that people who are sleepy will fall asleep more quickly compared to those with a sleep disorder.
For most people, it takes five to fifteen minutes to go into light sleep, but for people who have narcolepsy and idiopathic hypersomnia, it happens much faster. For patients with narcolepsy, it takes less than five minutes, while those who have idiopathic hypersomnia fall asleep in less than eight minutes.
People who sleep normally REM sleep usually occurs after one hour, and it is the same for idiopathic hypersomnia. But that is where IH and narcolepsy differ from one another. People with narcolepsy fall into REM sleep in less than fifteen minutes.
After the treatment, clinical neurophysiologist or sleep specialist read the results and then send them to the doctor that ordered this kind of test. It can take about two weeks to get the results.
The cost of a multiple sleep latency test can vary depending on the sleep clinic. The ones that some hospitals provide are offering lower expenses compared to the ones in the sleep clinic. The price ranges from 600 dollars to 2200 dollars.
Many professionals respect this test because the results that it provides are consistent, but it does not offer a 100% diagnosis for any disorder mostly because normal sleep latency is yet to be confirmed. But on the other hand, it can provide valuable insight to symptoms of sleep disorders that cause seizures, sleep apnea and distinguish narcolepsy from idiopathic hypersomnia.
Since we mentioned many times PSG test and disorders like narcolepsy and idiopathic hypersomnia, we will provide you with some facts about it.
What is Polysomnography?
PSG or polysomnography is a test that is you take while you are sleeping. A doctor supervises you as you sleep, and record information about the pattern of your sleep and possible symptoms of sleep disorders. These are the things that will be measured:
- Eye movement
- Breathing and heart rate
- Levels of blood oxygen
- The activity of the skeletal muscles
- Brain waves
Polysomnography notices the shift between non-REM and REM sleep. Non-REM sleep is separated into light and deep sleep. When you are in REM sleep the brain activity is very high. This is also the stage when dreams occur. In non-REM sleep, the activity of the brain is slower. A typical sleeper experiences 4-6 cycles each night.
As the sleep specialist observes your sleeping cycle, possible changes and how your body reacts to them, he/she can detect sleep disruptions and help you identify them.
How Does Polysomnography Work?
Major hospitals or sleep centers offer this kind of testing, and it occurs in the evening 2h before your sleep time (as we mentioned the night before MSLT). Since you will stay overnight, the center will provide you with a room similar to a room in a hotel. Of course, you can bring your own PJ and everything that is essential for your bedtime routine. A specialist observes the patient while sleeping, and because the specialist will hear and see inside the room, you will be able to consult during the night.
In order to measure stated parameters and record them, the specialist will have to put wired electrodes on your scalp, legs, chest, and temples. The sensors have patches that are adhesive so that they won’t fall off during the night and those sensors have thin wires that send information to a computer. Some sleep centers offer a possibility to record a video of that data. That way you and your doctor can review changes in the position of your body during your sleep.
To be fair, you probably won’t feel that comfortable enough to stay asleep as you would back home but don’t worry that won’t affect the results of the test.
Once you wake up the specialist will take off the sensors; you can leave and continue with your daily activities.
What is the Purpose of Polysomnography?
Polysomnography is used to monitor your sleep and determine when and why are your sleep patterns disrupted. During REM sleep, the waves in your brain slow down drastically based on EEG.
In non-REM stage, your eyes do not move as much but after a few hours the brain waves speed up, and the REM stage begins where most dreams occur. You usually enter many sleep cycles, and a cycle between non-REM and REM takes about ninety minutes, but sleep disorders can disrupt that process.
The doctor might recommend this test if he or she thinks there might be a chance that you have:
- Narcolepsy – If you feel overwhelming daytime drowsiness and experience sudden sleep attacks.
- Sleep apnea – If your breathing occasionally stops during sleep.
- REM sleep behavior disorder – If you start to act out your dreams while you sleep.
- Periodic limb movement disorder – If you move your limbs uncontrollably similar to restless leg syndrome.
- Strange behavior while sleeping – such as sleepwalking or sleep talking
- Chronic insomnia – If you experience difficulty falling or staying asleep.
This sleep disorder belongs in a category called Central Disorders of Hypersomnolence. The ICSD- 3 explains that most people with this disorder complain that despite regular sleep they feel sleepy during the day. Also, it makes waking up in the morning or after a nap harder.
The difference between other sleep disorders and hypersomnolence is that other disorders are caused by disruption of sleep while this disorder does not have an external cause. However, even if a person sleeps normally, he or she cannot feel rested or refreshed.
The feeling of being sleepy can occur at any time like at work or while you’re driving which is why idiopathic hypersomnia can be dangerous.
Idiopathic hypersomnia symptoms:
- Excessive daytime sleepiness
- The difficulty of waking up in the morning despite multiple alarms
- Sleep inertia – a state of feeling confused and disoriented after waking up
- Long naps after which a person doesn’t feel refreshed
- Memory problems and difficulty with attention and concentration.
Difference Between Idiopathic Hypersomnia and Narcolepsy
To understand the difference between IH and narcolepsy, it is best to use the MSLT. The first type of narcolepsy can be distinguished easily because cataplexy is usually linked to it. In the second type of narcolepsy, the cataplexy is non-existent. The multiple sleep latency tests can help understand the difference between those the two.
In people who have idiopathic hypersomnia and narcolepsy, sleep latency happens at a faster pace, but the difference is that narcolepsy patients have a shorter sleep latency of five or less minutes (that is eighty percent shorter than in other people).
Patients that have narcolepsy also have rapid experience of sleep onset REM stage. It is quite common for a person to experience sleep paralysis immediately, but in most cases, narcoleptics go to REM stage in less than 15 min. Unlike the people who have idiopathic hypersomnia have normal sleep onset REM period from seventy to ninety minutes.