Sleep Lab Tests to Diagnose Narcolepsy
To confirm a diagnosis of narcolepsy, your doctor may order 2 different types of sleep studies. These sleep tests take place in a sleep lab located in a hospital or sleep clinic. Theses test are usually ordered after your doctor performs a physical exam, looks at your sleep diary, and has you take a questionnaire about daytime sleepiness.
These tests often include polysomnography, a multiple sleep latency test, and actigraphy.1,3
What is polysomnography?
Polysomnography (PSG or sleep study) is an overnight sleep test that records brain and muscle activity, breathing, and eye movements. This test can tell your doctor whether your REM sleep is happening at the right times. It will also tell your doctor if you have other sleep disorders such as sleep apnea or periodic limb movement disorder.
During a sleep study, sensors record brain waves, oxygen levels in the blood, heart rate, breathing, body position, body temperature, and any eye, leg, or arm movements. Sleep cycles and sleep stages are also measured. Video may be used to record sound and movements.
You will sleep in a bed in a room more like a private hotel room than a hospital. This is to help you feel comfortable enough to sleep more naturally.
You will need to get enough sleep in days before the PSG. On the day of the test, you will be asked to avoid any sleep medicines, alcohol, caffeine, vigorous exercise, and naps. You may be asked to stop certain medicines up to 3 to 6 weeks before your sleep study.1,4
For a study at a sleep center, you will be asked to arrive 2 hours early. Once you are in bed, you will have sensors placed on your head, eyes, mouth, nose, chin, chest, legs, and arms. These sensors will measure everything from heart rate and eye movement to breathing. A technologist will monitor your sleep.
The sensors will measure:1,3-5
- How long it takes you to fall asleep
- How long it takes you to enter REM sleep
- How long you remain in each stage of sleep
- How often you wake up and how long it takes you to fall back asleep
- Whether you stop breathing or struggle to breathe
- Whether you move your arms or legs during sleep
What is the multiple sleep latency test (MSLT)?
A multiple sleep latency test (MSLT) usually takes place after the day after a PSG. It is also called a daytime nap study. It is a sleep lab test that measures how quickly someone falls asleep, and when and if they enter REM sleep.
Over the course of 1 day, there are 5 scheduled naps separated by 2-hour breaks. For each nap, the room gets dark and the person is asked to lay down and sleep for 20 minutes. Sensors record the sleep and its stages. Falling asleep within 8 minutes or going into REM sleep within 15 minutes suggests narcolepsy.1,6
MSLT results may not be accurate for people with Type 2 narcolepsy (without cataplexy), older adults, shift workers, and those with untreated sleep apnea.3
What is actigraphy?
Actigraphy is a device worn on your wrist. Your doctor may ask you to wear one for 2 weeks before your sleep lab test. Actigraphy helps your doctor understand your sleep patterns and rule out other sleep disorders.2
Other tests for narcolepsy
The results from a PSG and MSLT usually provide enough information to diagnose narcolepsy. However, some people involved in research studies or who have unusual symptoms may also need a spinal tap (lumbar puncture). A spinal tap will collect fluid that is tested to see if you have low levels of a brain chemical called hypocretin. Hypocretin is often low in people who have narcolepsy with cataplexy, called Type 1 narcolepsy.1,3
There is a genetic test for narcolepsy, but it is rarely used outside of research studies. More than 90 percent of people with Type 1 narcolepsy with cataplexy test positive for the gene group DQB1*0602. However, many healthy people also test positive for DQB1*0602.3