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).

• Response to each question on a scale from 0 (not at all likely to fall asleep) to 3 (very likely to fall asleep) is obtained.
  
  
• The resulting total score is between 0 and 24.
  
  
• Although what score constitutes abnormal sleepiness is controversial, total scores above 10 generally warrant investigation.
  
  
• You can take the Epworth Sleepiness Scale Test.

Polysomnography

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:

• Electrical activity of the brain (electroencephalogram)
  
  
• Electrical activity of the heart (electrocardiogram)
  
  
• Movements of the muscles (electromyogram)
  
  
• Eye movements (electrooculogram)
  
  
• Respirations (oral thermistor or nasal pressure transducer)

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). 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 10-20 minutes 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. 

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.