Causes and Diagnoses

Causes and Diagnoses of Narcolepsy

The cause of narcolepsy is still unknown, but research suggests many people who have narcolepsy with cataplexy have low levels of the neurotransmitter hypocretin, the chemical that regulates arousal, wakefulness and appetite.


  1. Have you ever had the sudden urge to sleep during the day even though you get enough sleep at night?
  2. Have you fallen asleep while working, eating or speaking with someone?
  3. Have you felt alert after a brief nap, but then your alertness quickly changes to sleepiness?

If you answered yes to any of these three questions, there is a chance that you have narcolepsy. Narcolepsy is not a common sleep problem and many physicians have difficulty diagnosing it. Northwestern Medicine can help make the proper diagnosis.

Sleep medicine specialists may use a variety of diagnostic tests to determine if you have narcolepsy. Tests include:

Also known as a polysomnogram, a sleep study requires you to stay overnight at a Northwestern Medicine sleep center so a specialist can observe and measure your sleep. You will sleep with sensors attached to different parts of your body that record your brain waves, heartbeat and other aspects of your sleep.

Multiple sleep latency test (MSLT)

The multiple sleep latency test (MSLT), also known as a nap study, measures your daytime sleepiness. The test requires you to attempt to take multiple naps at a sleep lab at set times throughout the day. It is used to see how quickly you fall asleep in quiet daytime situations. For each nap trial, you are asked to lie quietly in bed in a dark room and try to go to sleep. Most people with narcolepsy fall asleep in an average of three minutes during the MSLT.

Hypocretin level measurement

In rare cases, your specialist will need to measure your hypocretin (orexin) levels. Hypocretin is the neurotransmitter that controls arousal, wakefulness and appetite. People with narcolepsy with cataplexy usually have a lack of hypocretin. Because this exam requires a lumbar puncture (spinal tap), it is rarely used.

Diagnostic Tests