Narcolepsy

Narcolepsy is a chronic disorder of unknown etiology. Its usual onset is during the second or third decade of life, and it rarely occurs before age five or after age 50. The disorder is seen with equal frequency in men and women. The case described includes the cardinal features of narcolepsy: excessive daytime somnolence, sleep paralysis, hypnagogic hallucinations (vivid dream-like hallucination at sleep onset) and cataplexy.

However, patients rarely experience the full tetrad of symptoms.

Narcolepsy results, in part, from an inappropriate intrusion of REM sleep, with its properties of atonia and visual hallucinations, into wakefulness and other stages of sleep. Excessive daytime sleepiness is the most common complaint and precedes episodes of daytime sleep attacks. This symptom is often associated with impaired memory, poor attention and concentration and automatic behavior.

Sleep paralysis and hypnagogic hallucinations occur when REM-associated atonia and vivid dream-like visual hallucinations, respectively, intrude into the transition between wakefulness and sleep. During sleep paralysis, the patient is conscious but unable to move the limbs. Hypnagogic hallucinations occur at sleep onset. Hypnopompic hallucinations occur on awakening. Both sleep paralysis and hypnagogic hallucinations can occur in patients without narcolepsy when normal sleep patterns are disrupted.

Cataplexy is a cardinal feature of narcolepsy. It represents the intrusion of REM-associated atonia into wakefulness. For a few seconds or, rarely, a few minutes, a loss of axial and/or appendicular muscle tone occurs without loss of consciousness. The longer the episode, the more likely it is to lead directly into REM sleep. This phenomenon is often precipitated by extremes in emotion, such as anger, fear, excitement or, most commonly, laughter. It may occur several times daily or not at all. Cataplexy is particularly dangerous if it occurs while a patient is driving, bathing or swimming. Disturbed nocturnal sleep, characterized by frequent awakenings and body movements, is a common complaint, but is not a major cause of excessive daytime sleepiness. The incidence of sleep apnea and periodic limb movements of sleep in patients with narcolepsy is higher than that seen in the general population, but treatment of these two conditions does not improve daytime sleepiness.

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