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Narcolepsy Exams and Tests
Epworth Sleepiness Scale
Questionnaires are used to measure excessive sleepiness. The most commonly used questionnaire is the 8-question Epworth Sleepiness Scale (1991).
For this exam, one needs to come to a sleep laboratory about two hours prior to bedtime without making any changes in the daily habits. Then, the whole night's sleep is monitored and recorded. The following parameters are monitored:
These parameters are monitored as one passes through the various sleep stages (see Sleep: Understanding the Basics).
If a person has narcolepsy, the polysomnograph shows short sleep latency of usually less than five minutes and an abnormally short latency prior to the first sleep onset REM sleep (SOREMPs). During a daytime sleep study or nap study called a Multiple Sleep Latency Test (MSLT), more than two SOREMPs and a mean sleep latency of less than five minutes strongly suggest narcolepsy.
Multiple Sleep Latency Test
In this test, the time taken by a person to fall asleep (sleep latency) during the day while lying in a quiet room is measured. This test is performed the morning after the overnight polysomnogram. The person takes 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 10-20minutes to fall asleep. Persons with narcolepsy (and other causes of abnormal sleepiness) take a much shorter time (less than five minutes) to go from wakefulness into sleep.
This test is not routinely done in isolation, but may be part of a full evaluation of a patient for hypersomnia. Two weeks prior to these tests, the patient is asked to keep a sleep diary that records bedtime, wake-up times, and nap times. Their physician will inform them to gradually eliminate medications that could affect the sleep tests.
CSF (cerebrospinal fluid) hypocretin test
This has not yet become part of the routine diagnostic tools for narcolepsy, but is being used more frequently. For this test a sample of cerebrospinal fluid is removed by lumbar puncture and sent to the laboratory for analysis. The specificity and sensitivity of the CSF hypocretin test are high enough that it should have clinical usefulness for diagnosis. Thus, defining the precise criteria for the diagnosis of narcolepsy and other sleep disorders is an evolving process.
Medically Reviewed by a Doctor on 2/1/2016
Selim R Benbadis, MD
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