How is Narcolepsy Diagnosed?

It can take as long as 10 to 15 years after the first symptoms appear before narcolepsy is recognized and diagnosed. Many doctors are unfamiliar with narcolepsy, even though it affects 1 in 2,000 people. Narcolepsy symptoms are like symptoms of other illnesses, such as infections, depression, and sleep disorders.

Narcolepsy sometimes is mistaken for learning problems, seizure disorders, or laziness, especially in school-aged children and teens. When narcolepsy symptoms are mild, the disorder is even harder to diagnose.

Your doctor will diagnose narcolepsy based on your signs and symptoms, your medical and family histories, a physical exam, and test results.

Diagnosing Narcolepsy

Signs and Symptoms

Tell your doctor about any signs and symptoms of narcolepsy. This is important because your doctor may not ask about them during a routine checkup.

Your doctor will want to know when you first had signs and symptoms and whether they bother your sleep or daily routine. He or she also will want to know about your sleep habits and how you feel and act during the day.

To help answer these questions, you may want to keep a sleep diary for a few weeks. Keep a daily record of how easy it is to fall and stay asleep, how much sleep you get at night, and how alert you feel during the day.

Medical and Family Histories

Your doctor may ask whether:

  • You’re affected by certain factors that can lead to narcolepsy. Examples of these factors include infections, brain injuries, and autoimmune disorders. Some research suggests that environmental toxins may play a role in triggering narcolepsy.
  • You take medicines and which ones you take. Some medicines can cause daytime sleepiness. Thus, your symptoms may be due to medicine, not narcolepsy.
  • You have symptoms of other sleep disorders that cause daytime sleepiness.
  • You have relatives who have narcolepsy or who have signs or symptoms of the disorder.

Physical Exam

Your doctor will check you to see whether another condition is causing your symptoms. For example, infections, certain thyroid diseases, drug and alcohol use, and other medical or sleep disorders may cause symptoms similar to those of narcolepsy.

Diagnostic Tests

Sleep Studies

If your doctor thinks you have narcolepsy, he or she will likely suggest that you see a sleep specialist. This specialist may advise you to have sleep studies to find out more about your condition. Sleep studies are done at sleep centers. Doctors use the results from two tests to diagnose narcolepsy. These tests are a polysomnogram (PSG) and a multiple sleep latency test (MSLT).

Polysomnogram. You usually stay overnight at a sleep center for a PSG. The test records brain activity, eye movements, heart rate, and blood pressure. A PSG can help find out whether you:

  • Fall asleep quickly
  • Go into rapid eye movement (REM) sleep soon after falling asleep
  • Wake up often during the night

Multiple sleep latency test. This daytime sleep study measures how sleepy you are. It’s often done the day after a PSG. During the test, you’re asked to nap for 20 minutes every 2 hours throughout the day. (You will nap a total of four or five times.) A technician checks your brain activity during this time. He or she notes how quickly you fall asleep and how long it takes you to reach various stages of sleep.  An MSLT finds out how quickly you fall asleep during the day (after a full night’s sleep). It also shows whether you go into REM sleep soon after falling asleep.

Other Tests

Hypocretin test. This test measures the level of hypocretin in the fluid that surrounds your spinal cord. Most people who have narcolepsy have low levels of hypocretin. Hypocretin is a chemical that helps promote wakefulness. Please note: spinal taps are rarely used to diagnose narcolepsy.

Video on Narcolepsy Diagnosis