A narcolepsy diagnosis requires several tests. A doctor will perform a physical exam and an in-depth medical history to rule out other causes of symptoms. Keep in mind that having some of the major symptoms of narcolepsy doesn't necessarily mean you have narcolepsy.
In addition, several specialized tests, which can be performed in a sleep disorders clinic, usually are required before a diagnosis can be established. Two tests that are considered essential in confirming a diagnosis of narcolepsy are the polysomnogram (PSG) and the multiple sleep latency test (MSLT). In addition, questionnaires, such as the Epworth Sleepiness Scale, are often used to measure excessive daytime sleepiness.
Epworth Sleepiness Scale
During the Epworth Sleepiness Scale test, you will be asked to answer eight questions using a scale from zero (not at all likely to fall asleep) to three (very likely to fall asleep). The resulting total score is between 0 and 24. Scores of 0 to 10 are normal. Total scores 10 or above generally warrant further investigation.
A sleep study, or polysomnogram (PSG), is a test performed in a sleep lab. It electronically transmits and records specific physical actions of the body while you sleep, such as muscle movement, breathing patterns, and brain activity. The recordings are analyzed by a qualified sleep specialist to determine whether or not you have a particular sleep disorder.
What to Expect During a PSG
If you're scheduled for a PSG, you will arrive at the sleep lab about two hours prior to bedtime without making any changes in your daily habits. You will be assigned to a private bedroom in a sleep center or hospital. Near the bedroom will be a central monitoring area, where the technicians will monitor you while you sleep. You will be hooked up to equipment that may look uncomfortable. However, most people fall asleep with little difficulty. Your whole night's sleep will be monitored and recorded.
Multiple Sleep Latency Test
Performed the morning after the overnight polysomnogram, also in a sleep lab, this test measures how long it takes a person to fall asleep (sleep latency) during the day. During this test, you will be asked to take four or five scheduled naps every two hours. The first nap starts two hours after awakening that morning. People with normal sleep and alertness take about 10-20 minutes to fall asleep. People with narcolepsy (and other causes of abnormal sleepiness) take a much shorter time (less than five minutes) to fall asleep.
Two weeks prior to these tests, you will be asked to keep a sleep diary that records bedtime, wakeup times, and nap times. Your doctor will work with you to create a plan to gradually eliminate medications that could affect the sleep test results.