How Is Narcolepsy Diagnosed?

Doctors will base a diagnosis of narcolepsy on the patient’s symptoms, family history of narcolepsy, physical exam, and test results. The symptoms people have are often distinct enough for doctors to diagnose narcolepsy. But laboratory tests are needed to confirm the diagnosis and determine the best treatment. These tests may require the patient to visit a sleep disorders center for an overnight evaluation.

Symptoms and Family History

If your doctor suspects you have narcolepsy, he or she will ask whether you have:

• Daytime sleepiness and sleep attacks
• Sudden and temporary losses of muscle tone and control (cataplexy)
• Vivid dreams while falling asleep or waking up (hallucinations)
• An inability to move or speak while falling asleep or waking up (sleep paralysis)

If you have any of these symptoms, your doctor will want to know when you first developed them and if they interfere with sleep or daily activities. The doctor may also ask questions about your sleep habits and how you feel and act during the daytime. To help you answer those questions, you may be asked to keep a sleep diary for a few weeks. In this daily dairy you may be asked to write:

• When you go to bed and get up
• How long it takes you to fall asleep, and how often you wake up during the night
• If you snore loudly and frequently, or wake up gasping or feeling out of breath
• How refreshed you feel when you wake up, and how tired you feel during the day
• How often you doze off or have trouble staying awake during the day

Doctors also usually ask whether you have symptoms of other sleep disorders that cause daytime sleepiness. You may also be asked if you have any relatives with narcolepsy.

Physical Exam

Your doctor will examine you to see if you have signs of other possible causes for your symptoms. These causes include:

• Infections
• Certain thyroid diseases
• Drug or alcohol use
• Other medical or sleep disorders

This part of the diagnosis usually requires your doctor to do a complete physical exam.

Sleep Specialist

If your doctor suspects you have narcolepsy, he or she will likely suggest you see a sleep specialist who may recommend special sleep tests. The sleep specialist will confirm a diagnosis of narcolepsy, diagnose another sleep disorder, or rule out a specific sleep disorder as the cause of your symptoms, based on:

• The results of your sleep tests
• Your symptoms
• Your sleep habits as recorded in a sleep diary

Narcolepsy is easier to diagnose if you have more symptoms than just daytime sleepiness and sleep attacks.

Sleep Tests

Sleep tests are usually done at a sleep disorders center. For some sleep tests, you may need to sleep overnight at the center. Other sleep tests can be done during the day. The three tests most often used to diagnose narcolepsy are:

• Polysomnogram (PSG)
• Multiple sleep latency test (MSLT)
• Hypocretin test

Polysomnogram

For this study, you sleep overnight at a sleep center. While you are sleeping, the staff at the center use various devices to measure your brain activity, breathing, and movements. The signs of narcolepsy this test can reveal include:

• Falling asleep quickly
• Entering rapid eye movement (REM) sleep soon after falling asleep
• Waking up often during the night

Multiple Sleep Latency Test

This test is usually done during the day after an overnight PSG. Also called a nap study, the MSLT measures how easy it is for you to fall asleep during the day. You are asked to take short naps about every 2 hours. The test records eye movements, muscle tone, and brain activity with small devices attached to the head. The signs of narcolepsy this test can reveal are quickly falling asleep during the day (after a full night’s sleep) and entering REM sleep soon after falling asleep.

Hypocretin Test

This test measures the levels of hypocretin in the fluid that bathes your spinal cord. Low levels of hypocretin make it likely that you have narcolepsy.