Narcolepsy is a sleep disorder marked by excessive sleepiness during the day or recurring, uncontrollable episodes of sleep during normal waking hours, plus sudden episodes of muscle weakness (cataplexy). Sometimes sleep paralysis, vivid dreams, and hallucinations while falling asleep or waking up from sleep also occur.
Narcolepsy occurs in fewer than 1 of 2,000 people in the United States and Europe. It is equally common among men and women. In some cases, the disorder tends to run in families, but environmental factors also seem to be involved. The cause is unknown. Some evidence suggests that narcolepsy may be caused by an autoimmune reaction (when the immune system attacks the body's own tissues) that destroys nerve cells in a certain area of the brain.
Although narcolepsy has no serious medical consequences, it can be disabling and increases the risk of motor vehicle and other accidents. Narcolepsy persists throughout life but does not affect life expectancy.
Narcolepsy reflects, in part, abnormalities in the timing and control of rapid eye movement (REM) sleep. Many symptoms resemble what happens during REM sleep. The muscle weakness, sleep paralysis, and hallucinations of narcolepsy resemble the loss of muscle tone, paralysis, and vivid dreaming that occur during REM sleep.
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. All have excessive daytime sleepiness (EDS).
People with narcolepsy have EDS, often despite long periods of excessive sleep. Many people are overcome by sudden episodes of uncontrollable sleep that can occur at any time, often without warning (called sleep attacks). Falling asleep can be resisted only temporarily. People may have many episodes or only a few in a single day. Each usually lasts a few minutes or less but may last hours. People can be awakened as readily as from normal sleep. They typically feel refreshed when they wake up even when the sleep episode lasts a few minutes. However, they may fall asleep again in a few minutes.
Episodes of falling asleep are most likely to occur in monotonous situations, as during boring meetings or long periods of highway driving, but may occur while eating, speaking, or writing. Nighttime sleep may be unsatisfying and interrupted periodically by awakenings and vivid, frightening dreams.
While people are awake during the day, 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. People may become limp, drop something being held, or fall to the ground. The jaw may droop, facial muscles may twitch, eyes may close, and the head may nod. People may slur their speech.
These episodes resemble the normal muscle paralysis that occurs during rapid eye movement (REM) sleep and, to a lesser degree, the experience of being “weak with laughter.”
Cataplexy occurs in fewer than 3 of 4 people with narcolepsy.
Occasionally, when just falling asleep or immediately after awakening, people try to move but cannot. This experience, calledsleep paralysis, can be terrifying. The touch of another person may relieve the paralysis. Otherwise, the paralysis disappears on its own after several minutes.
Sleep paralysis occurs in about one fourth of people with narcolepsy. It sometimes occurs in healthy children and, less often, in healthy adults.
When just falling asleep or, less often, when awakening, people may clearly see images or hear sounds that are not there. These extremely vivid hallucinations are similar to those of normal dreaming but are more intense. Hallucinations are called
Hypnagogic hallucinations occur in about one third of people with narcolepsy. They are common among healthy children and occasionally occur in healthy adults.
Doctors suspect narcolepsy when people with excessive daytime sleepiness have had episodes of muscle weakness. However, doctors cannot base the diagnosis on symptoms alone because other disorders can cause some of the same symptoms. Sleep paralysis and similar hallucinations occasionally occur in otherwise healthy adults, in people who have been sleep deprived, and in people with sleep apnea syndrome or depression. These symptoms may also occur when certain drugs are taken. Therefore, testing in a sleep laboratory is necessary.
Sleep testing in a sleep laboratory consists of polysomnography, done overnight, and multiple sleep latency testing, done the next day. These tests involve monitoring and recording the activity of the brain, heart, breathing, muscles, and eyes. Various other body functions, including movement of the limbs, are also monitored and recorded.
Usually, narcolepsy does not result from abnormalities that can be detected by imaging procedures, such as computed tomography (CT) or magnetic resonance imaging (MRI).
There is no cure for narcolepsy. However, for many people, continued treatment results in normal lives.
People should also try to get enough sleep at night and take brief naps (less than 30 minutes) at the same time every day (typically afternoon). If symptoms are mild, these measures may be all that is needed.
For others, drugs that help keep people awake, such as modafinil (or sometimes armodafinil, dextroamphetamine, or methylphenidate), are used to help reduce the sleepiness. The dose of these drugs may have to be adjusted to prevent side effects such as jitteriness, overactivity, nausea, headache, or weight loss. Doctors monitor people closely during drug treatment. Dextroamphetamine and methylphenidate are stimulants, which may cause agitation, high blood pressure, a fast heart rate, and moodiness. These drugs may also be habit-forming. Modafinil and armodafinil, which work in a slightly different way from dextroamphetamine and methylphenidate, may have fewer side effects than the other drugs and are less likely to be habit-forming.
Sodium oxybate, a drug taken while in bed and again during the night, can usually lessen excessive daytime sleepiness and cataplexy. Side effects include nausea, vomiting, dizziness, urinary incontinence (involuntary urination), and sleepiness.
An antidepressant, such as clomipramine, protriptyline, venlafaxine, or fluoxetine, usually helps relieve cataplexy, hallucinations, and sleep paralysis.