Section 6. Brain, Spinal Cord, and Nerve Disorders

Chapter 81. Sleep Disorders

Topics: Introduction | Insomnia | Hypersomnia | Narcolepsy | Sleep Apnea Syndromes | Parasomnias | Sleep Disorders in People With Dementia

Narcolepsy

Narcolepsy is a sleep disorder marked by recurring, uncontrollable episodes of sleep during normal waking hours, as well as by sudden episodes of muscle weakness (cataplexy), sleep paralysis, and hallucinations.

Narcolepsy occurs in about 1 of 200,000 people. The disorder tends to run in families, but its cause is unknown. Although narcolepsy has no serious medical consequences, it can be disabling and may increase the risk of motor vehicle and other accidents.

Symptoms

Symptoms usually begin during adolescence or young adulthood and persist throughout life. Only about 10% of people with narcolepsy have all the symptoms; most people have only a few.

People with narcolepsy are overcome by sudden episodes of uncontrollable sleepiness that can occur at any time. Falling asleep can be resisted only temporarily. A person may have many episodes or only a few in a single day; each usually lasts half an hour or less. Episodes are most likely to occur in monotonous situations, such as during boring meetings or long periods of highway driving. When intentionally taking short naps, the person usually feels refreshed after awakening.

A sudden episode of muscle weakness without loss of consciousness--called cataplexy--may be triggered by a sudden emotional reaction such as anger, fear, joy, laughter, or surprise. The person may become limp, drop something being held, or fall to the ground. These episodes resemble the muscle relaxation that occurs during REM sleep and, to a lesser degree, the experience of being "weak with laughter."

Occasionally, when just falling asleep or immediately after awakening, the person tries to move but cannot. This experience, called sleep paralysis, can be terrifying. The touch of another person may relieve the paralysis. Otherwise, the paralysis disappears on its own after several minutes.

When just falling asleep or, less often, when awakening, the person may clearly see images or hear sounds that are not there. These extremely vivid hallucinations (called hypnagogic hallucinations) are similar to those of normal dreaming but are more intense.

Diagnosis and Treatment

The diagnosis is usually based on the symptoms, but the same symptoms can be caused by other disorders. Sleep paralysis and hallucinations occasionally occur in otherwise healthy adults. If the diagnosis is uncertain, electroencephalography (EEG), which records the brain's electrical activity (see Section 6, Chapter 77), is performed, usually in a sleep laboratory. If a person has narcolepsy, EEG typically shows that REM-type sleep activity occurs as the person falls asleep, rather than later in the sleep cycle as it normally does. Usually, narcolepsy does not result from abnormalities that can be detected by imaging procedures.

Stimulant drugs, such as amphetamine, dextroamphetamine, methylphenidate, modafinil, and pimoline, may help reduce the sleepiness. The dose may have to be adjusted to prevent side effects such as jitteriness, overactivity, or weight loss. Consequently, doctors monitor people closely when they begin drug treatment. Modafinil may have fewer side effects than the other drugs. An antidepressant such as imipramine usually helps relieve cataplexy. Frequent, short (15- to 20-minute) naps during the day often help.