(See also Overview of Sleep.)
Narcolepsy occurs in about 1 of 2,000 people in the United States, Europe, and Japan. It is equally common among men and women.
What causes narcolepsy is unknown. Some people with narcolepsy have a similar group of genes, but the cause is not thought to be genetic. Environmental factors seem to be involved and may trigger the disorder. Some evidence suggests that narcolepsy may be caused by an autoimmune reaction that destroys nerve cells in a certain area of the brain. (An autoimmune reaction occurs when the immune system attacks the body's own tissues.)
People with narcolepsy sleep a lot during the day. As a result, narcolepsy 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.
Idiopathic hypersomnia, like narcolepsy, results in excessive daytime sleepiness. Polysomnography and a multiple sleep latency test are needed to help determine which of the two disorders is causing excessive daytime sleepiness.
Symptoms of narcolepsy usually begin during adolescence or young adulthood and persist throughout life.
The main symptoms are
Only about 10% of people with narcolepsy have all the symptoms. Most people have only a few. All have excessive daytime sleepiness.
People with narcolepsy have excessive daytime sleepiness, 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.
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. Vision may be blurred. 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 causes significant problems in about one fifth of people with narcolepsy.
Occasionally, when just falling asleep or immediately after awakening, people try 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.
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.
People with narcolepsy often have difficulty functioning and concentrating. They are more likely to injure themselves—for example, if they fall asleep while driving. Narcolepsy can cause stress. Productivity and motivation may decrease, and concentration may be poor. People may withdraw from others and thus damage personal relationships. Many become depressed.
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 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 is usually done in a sleep laboratory, which may be located in a hospital, clinic, hotel room, or other facility that is equipped with a bed, bathroom, and monitoring equipment. Electrodes are pasted to the scalp and face to record the brain's electrical activity (electroencephalography, or EEG) as well as eye movements. Applying these electrodes is painless. The recordings help provide doctors with information about sleep stages. Electrodes are also attached to other areas of the body to record heart rate (electrocardiography, or ECG), muscle activity (electromyography), and breathing. A painless clip is attached to a finger or an ear to record oxygen levels in the blood. Polysomnography can detect breathing disorders (such as obstructive sleep apnea), seizure disorders, narcolepsy, periodic limb movement disorder, and unusual movements and behaviors during sleep (parasomnias). Polysomnography is now commonly done in the home to diagnose obstructive sleep apnea, but not any other sleep disorders.
A multiple sleep latency test is done to distinguish between physical fatigue and excessive daytime sleepiness and to check for narcolepsy. People spend the day in a sleep laboratory. They are given the opportunity to take five naps at 2-hour intervals. They lie in a darkened room and are asked to take a nap. Polysomnography is used as part of this test to assess how quickly people fall asleep. It detects when people fall asleep and is used to monitor the stages of sleep during the naps and to determine whether REM (dreaming) sleep occurs. During multiple sleep latency testing, people with narcolepsy typically fall asleep quickly and have at least two REM naps.
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 brain imaging procedures, such as computed tomography (CT) or magnetic resonance imaging (MRI). However, doctors may use brain imaging and blood and urine tests to rule out other disorders that can cause excessive daytime sleepiness.
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, armodafinil, solriamfetol, pitolisant, or sodium oxybate are used to help reduce the sleepiness. Doctors monitor people closely during drug treatment.
Dextroamphetamine and methylphenidate, which are stimulants, are used only if other narcolepsy drugs are ineffective or cause intolerable problems. These drugs can cause agitation, high blood pressure, a fast heart rate, and moodiness. They may also be habit-forming.
Modafinil, armodafinil, solriamfetol, and pitolisant work in a slightly different way from dextroamphetamine and methylphenidate, have fewer side effects, and are less likely to be habit-forming. Thus, these four drugs are the preferred treatment for people who have narcolepsy without cataplexy. Pregnant women should not take modafinil because it may cause severe birth defects, including heart defects.
Sodium oxybate, a drug taken while in bed and again during the night, can usually lessen excessive daytime sleepiness and cataplexy. Sodium oxybate is the preferred treatment for people with narcolepsy and cataplexy. Side effects include nausea, vomiting, dizziness, urinary incontinence (involuntary urination), sleepiness, and sometimes sleepwalking.