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Tests and diagnosis
By Mayo Clinic staffYour doctor may make a preliminary diagnosis of narcolepsy based on your experience of both excessive daytime sleepiness and sudden loss of muscle tone (cataplexy). After an initial diagnosis, your doctor may refer you to a sleep specialist for more evaluation.
Formal diagnosis may require staying overnight at a sleep center where you undergo an in-depth analysis of your sleep by a team of specialists. Methods of diagnosing narcolepsy and determining its severity include:
- Sleep history. Your doctor will want to obtain from you a detailed history so that the onset of your illness, and any other factors that could help explain your symptoms, are fully considered. A part of the history involves filling out the Epworth Sleepiness Scale, which uses a series of short questions to gauge your degree of sleepiness. You'll rank on a numbered scale how likely it is that you would doze off in certain situations, such as sitting down after lunch.
- Actigraphy. You may be asked to keep a detailed diary of your sleep pattern for a week or two, so that your doctor can compare how your sleep pattern and alertness are related. Often, in addition to this "sleep log," the doctor will ask you to wear an actigraph. This device has the look and feel of a wrist watch and measures how and when you sleep.
- Polysomnogram. This test measures a variety of signals during sleep using electrodes placed on your scalp before you fall asleep. For this test, you must stay overnight for observation at a medical facility. The test measures the electrical activity of your brain (electroencephalogram) and heart (electrocardiogram), the movement of your muscles (electromyogram) and eyes (electro-oculogram), and monitors your breathing.
- Multiple sleep latency test. This examination measures how long it takes for you to fall asleep during the day. You'll be asked to fall asleep for a series of four or five naps, each nap two hours apart. Specialists will observe your sleep patterns. People who have narcolepsy fall asleep easily and enter into rapid eye movement (REM) sleep quickly.
These tests can also help doctors rule out other possible causes of your signs and symptoms. Other sleep disorders, such as sleep apnea, can cause excessive daytime sleepiness.
