Epidemiology

Since many individuals are unaware that excessive sleepiness may be indicative of a disorder (rather than plain exhaustion) narcolepsy often goes unrecognized. It can begin before the age of 10 or as late as 50, however narcolepsy usually occurs between the ages of 15 and 35 (Aldrich, 1990).

Prevalence of narcolepsy has been indicated to be between 0.02% to 0.16% in the adult population. Examples of epidemiological studies, which indicate the prevalence, are as follows:

• In the San Francisco Bay area, Dement, Zarcone, and Varner (1972) have calculated the prevalence as 0.05%.
• Lavie and Peled (1987) found the prevalence of narcolepsy in Japan to be about 1 in 500,000.
• On the other hand, Honda (1988) determined the prevalence of narcolepsy to be 1 in 600 in Japan.
• Dement, Carskadon, and Ley (1973) calculated the prevalence in Europe as 1 in 1000.
• In the USA, Roth (1980) determined the prevalence to be approximately 1 in 10,000.

Studies have found that narcolepsy affects both men and women equally (Aldrich, 1990; DSM-IV, 1994). "Special circumstances, such as an abrupt change of sleep-wake schedule and/or a severe psychological stress (for example, death of a relative or divorce) precede the occurrence of the first symptom in half the cases" (Guilleminault, 1994, p.338).