Intrinsic sleep disorders: Narcolepsy
Narcolepsy is a disorder of the control of sleep, particularly REM sleep.29 Patients with narcolepsy develop symptoms related to the inability to control the onset and offset of sleep or its fragments. The traditional tetrad of narcolepsy is
- excessive daytime sleepiness
- sleep paralysis
- hypnagogic hallucinations
Cataplexy, sleep paralysis, and hypnagogic hallucinations are features or fragments of REM sleep.
Patients may present with excessive daytime sleepiness alone. This sleepiness occurs despite relatively normal nocturnal sleep. These patients have irresistible bouts of sleep and fall asleep in inappropriate situations (e.g., in the middle of a conversation or while driving or eating).
Cataplexy, a second major symptom, consists of an abrupt decrease in muscle tone without loss of consciousness. Individuals who have severe attacks may fall or experience varied degrees of weakness. Strong emotional stimuli may provoke a cataplectic attack. Cataplectic attacks usually last less than 30 seconds.
Sleep paralysis is an inability to move during the transition into or out of sleep. These episodes may last several minutes and can be accompanied with the feeling of impending doom.
Occasionally, patients may have concurrent hallucinations. Hypnagogic hallucinations are vivid dreams that are difficult to distinguish from reality.
Narcolepsy is a genetic, nonprogressive disorder that appears in early adolescence and persists throughout life. Narcolepsy has a strong link to the DR2 (DR15) major histocompatibility complex and a weaker link to DQW1. HLA DQB1*0602 has demonstrated an even stronger linkage for narcolepsy. 30 This gene so far appears in 36% of those who were HLA-DR2 negative.
Narcolepsy is diagnosed by an appropriate history and physical examination and supported by short sleep latency and the presence of REM sleep in two or more naps on a multiple sleep latency test.