What tests are used to diagnose narcolepsy?

It's not unusual for people suffering from narcolepsy to visit a variety of healthcare professionals for years before they receive an accurate diagnosis. To get an accurate diagnosis, you should be seen in an accredited sleep center by a sleep specialist.

Two tests are used to diagnose narcolepsy. The nocturnal polysomnogram (sleep study) involves continuous recording of brain waves and several nerve and muscle functions during nighttime sleep. It also includes monitoring your breathing pattern and oxygen levels while you sleep. When tested, people with narcolepsy fall asleep rapidly, enter REM (rapid eye movement) sleep early and may wake often during the night. The polysomnogram also helps detect other possible sleep disorders such as sleep apnea that could cause daytime sleepiness.

The multiple sleep latency test (MSLT) measures the degree of daytime sleepiness and detects when REM sleep occurs. During this test, you're given a chance to sleep every two hours during normal wake times. A sleep specialist observes how long it takes you to fall asleep. People with narcolepsy fall asleep rapidly and enter REM sleep very early in their sleep cycle.
Dr. Mehmet Oz, MD
Cardiology (Cardiovascular Disease)
The following tests are used to diagnose narcolepsy:

1. Sleep Study or Polysomnogram (PSG): This painless test is done at night, usually at a sleep center. While you're sleeping, electrodes measure breathing, any breathing difficulty, oxygen levels, brain waves, eye and muscle movement, and your heart rate.

If there are any abnormalities to your sleep cycle—for example, you experience REM (rapid eye movement, which occurs when you're dreaming) at abnormal times—this will help the healthcare provider rule out other causes.

2. Multiple Sleep Latency Test (MSLT): The MSLT is completed during the day. It measures how long it takes you to fall asleep. You'll take a short nap a few times during the day. If you're able to fall asleep within 8 minutes and/or you achieve REM within a couple minutes of falling asleep, you may have narcolepsy.

Together, these two tests go a long way to helping determine whether you have narcolepsy, but they don't tell the whole story. If you don't experience cataplexy (sudden muscle tone loss) too, we need to rule out other potential causes of your sleepiness.

There is a third test—but it's not for everyone. It's called a human leukocyte antigen typing. It measures hypocretin, the brain chemical that is thought to cause narcolepsy in some cases. The test involves taking a sample of cerebrospinal fluid through your lumbar spine.

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