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. This is because narcolepsy is fairly rare. Also, many of the symptoms of narcolepsy are like symptoms of other illnesses, such as infections, depression, and sleep disorders.

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

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

Signs and Symptoms

Tell your doctor about any signs and symptoms of narcolepsy that you have. 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.

For a sample sleep diary, see the National Heart, Lung, and Blood Institute's "Your Guide to Healthy Sleep."

Medical and Family Histories

To learn about your medical and family histories, your doctor may ask whether:

• You're affected by certain factors that can lead to narcolepsy. These include infection, brain injuries, contact with toxins (such as pesticides), or autoimmune disorders.
• 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 examine 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 special sleep studies to find out more about your condition.

Sleep studies usually are done at a sleep center. The results of two tests—a polysomnogram (PSG) and a multiple sleep latency test (MSLT)—are used to diagnose narcolepsy.

Polysomnogram. You usually stay overnight at a sleep center for a PSG. The test records brain activity, eye movements, breathing, heart rate, and blood pressure. This test 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 relax in a quiet room for about 30 minutes. A technician checks your brain activity during this time. The test is repeated three or four times throughout the day.

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 levels of hypocretin in the fluid that surrounds your spinal cord. Most people who have narcolepsy have low levels of hypocretin.

To get a sample of spinal cord fluid, a spinal tap (also called a lumbar puncture) is done. For this procedure, your doctor inserts a needle into your lower back area and then withdraws a sample of your spinal fluid.