Narcolepsy is a difficult syndrome to diagnose because of its similarities to other sleep disorders. It must be differentiated from normal variations in sleep, sleep disorders, or mental illness. Essential features include "repeated irresistible attacks of refreshing sleep, cataplexy, and recurrent intrusions of elements of rapid-eye-movement (REM) sleep into the transition period between sleep and wakefulness" (DSM-IV, 1994).
Three tests have been designed to evaluate sleepiness objectively: Electronic pupillogram (EPG), the Multiple Sleep Latency Test (MSLT), and polysomngrapic monitoring.
1. Electronic Pupillogram (EPG): The EPG has been used as a means to measure decreased levels of sleepiness in those experiencing symptoms of narcolepsy. The data obtained from this test is difficult to interpret and diagnoses sleepiness rather than narcolepsy.
2. Multiple Sleep Latency Test (MSLT): Carskadon and Demnet designed the MSLT in 1982. Clinically, the MSLT is the most useful technique for diagnosing narcolepsy. For this test, a measurement of physiological sleep tendencies is obtained by calculating the latency between the time the lights go out and the time of sleep. Sleep is monitored during two-hour periods (Aldrich, 1990). "More than 80 percent of patients with narcolepsy have a mean sleep latency of less than five minutes and at least two REM periods at the onset of sleep during the procedure" (Aldrich, 1990, p.392). Scores for the MSLT vary with age and are rated as follows:
3. Polysomnographic Monitoring: This is a continuous 24-36 hour monitoring which "provides information about the actual number, duration, times, and types of daytime sleep episodes as well as disrupted night sleep" (Guilleminault, 1994, p.341).
Although each of these tests are beneficial, they should not be used as the sole item for a positive diagnosis of narcolepsy.
The positive diagnosis of narcolepsy requires sleepiness and/or cataplexy and must occur daily over a 3-month period (see the diagnostic requirement of the DSM-IV). The sleep attack is often the result of unintended sleep in inappropriate situations (i.e.: while driving). Typically these sleep attacks will last 10 to 20 minutes and will occur 2 to 6 times per day when untreated. Also, the sleep attacks may be accompanied by hallucinations, before sleep onset or immediately after awakening. Sleep paralysis may also occur.
Cataplexy, one of the two main symptoms of narcolepsy, occurs in approximately 70% of individuals with the disorder (DSM-IV, 1994). Usually cataplexy develops later on in life, years after being diagnosed with narcolepsy. A cataplexic attack last anywhere from a few seconds to a half and hour and is usually triggered by a strong emotional stimulus. (See "Symptoms")