Unknown: Narcolepsy

Definition
Description
Demographics
Causes and Symptoms
Diagnosis
Treatment
Prognosis
Prevention
The Future
For more information

Definition

Narcolepsy is a sleep disorder caused by the brain's inability to regulate normal sleep/wake cycles. People with narcolepsy have sleep episodes in the daytime, hallucinations when falling asleep or awaking, and often awaken at night.

Description

Narcolepsy can affect people in any age group but may not be diagnosed for as long as ten years after onset. It can be a disabling condition. Because people with narcolepsy can fall asleep in the daytime in the middle of other activities—including eating, driving, or operating heavy equipment—they can be involved in serious accidents. Children or adolescents with narcolepsy can fall behind in school or be judged as lazy students even though they are of normal intelligence.

Having narcolepsy does not mean that people with the disorder sleep more than other people. The disorder is better understood as a disturbance of the normal boundaries between sleeping and waking rather than simply sleeping too much. A normal adult who sleeps for about eight hours has between four and six sleep cycles during that time. A sleep cycle is a period of a type of sleep called non-rapid eye movement (NREM) sleep followed by a period of rapid eye movement (REM) sleep. REM sleep is

characterized by increased brain activity, rapid movement of the eyes below the lids, and sleep paralysis. People who say that they were having a dream when they woke up have been awakened from REM sleep. In normal adults, a sleep cycle is about 100–110 minutes long, 80–100 minutes of NREM sleep followed by 10–20 minutes of REM sleep.

In narcolepsy, however, the patient's sleep cycles do not follow this normal pattern. Instead, the person falls into REM sleep very shortly after falling asleep. In addition, the short periods of sleep that the patient has during the daytime are REM sleep. This abnormal occurrence of REM sleep helps to explain such symptoms of narcolepsy as sleep paralysis and cataplexy.

Demographics

It is possible that narcolepsy affects more people than is presently known. The rate of narcolepsy in the general population varies widely around the world. In Israel, for example, only about one person per 500,000 is diagnosed with narcolepsy whereas the rate in Japan is one person in every 600. In the United States, narcolepsy affects about one person in every 2,000. It is slightly more common in African Americans than in members of other races.

Narcolepsy affects men and women equally. It is not thought to be inherited. However, about 10 percent of Americans with narcolepsy have a relative with the condition, but this percentage is low compared to other disorders that are known to be purely genetic in origin.

Most cases of narcolepsy first appear in people between the ages of ten and twenty-five years, but the disorder has been diagnosed in children as young as three and in adults over fifty.

Causes and Symptoms

The basic cause of narcolepsy remains unknown. Progress has been made since the late 1990s in identifying two pieces of the puzzle. The first is a connection between narcolepsy and changes in a set of genes on chromo-some 6 called the HLA complex. It is thought that changes in these genes may be linked to the loss of cells in the brain that secrete hypocretin, a protein that regulates the sleep/wake cycle. Researchers do not know exactly what causes the loss of the brain cells that make hypocretin. Because the HLA complex has been linked to other autoimmune disorders, however, some doctors think that narcolepsy may be an autoimmune disease. No one has been able to prove this theory as of late 2008, however. Other researchers think that the hypocretin-producing cells may be damaged by some type of infection, but this theory has yet to be proved.

Narcolepsy has four primary symptoms:

• Excessive daytime sleepiness (EDS). This symptom may take the form of “microsleeps” of a few seconds, a long-lasting feeling of drowsiness, or daytime episodes of sleep lasting half an hour or longer.
• Cataplexy. Cataplexy refers to a sudden loss of muscle tone that may result in slurred speech, sagging of the facial muscles, general muscle weakness, inability to hold up one's head, buckling of the knees, or loss of strength in the arms. Cataplexy is often triggered by strong emotions, whether positive feelings like laughter or pleasant surprise or negative emotions like fear, shock, or anger. Cataplexy can last from a few seconds to as long as thirty minutes. The person is awake and alert during an episode of cataplexy even though he or she may appear unconscious to others.
• Hypnagogic hallucinations. Hypnagogic refers to the period of partial alertness that people have when they are waking up or falling asleep. People with narcolepsy experience very vivid and sometimes frightening dreams when they are half awake, and they may mistake these dreams for reality.
• Sleep paralysis. Sleep paralysis refers to a temporary inability to move or speak while falling asleep or waking up. These episodes last only one or two minutes and do not affect everyone with narcolepsy, but they can be frightening to patients who do have them.

Other symptoms experienced by some people with narcolepsy include automatic behavior, in which the person performs a routine task like sorting laundry or making a cup of coffee without conscious awareness or later memory of the action. People with narcolepsy may also thrash about in bed at night or act out their dreams by screaming or waving their arms.

Diagnosis

The diagnosis of narcolepsy is often delayed because its symptoms resemble those of such other disorders as depression, seizure disorders, simple lack of sleep, or even illegal drug use. Early diagnosis is important because the impact of the disorder on a person's education, employment, relationships, and self-esteem can be severe. According to one study, 24 percent of adults with narcolepsy had to quit working and 18 percent had been fired from their jobs because of the disease.

The diagnosis of narcolepsy is based on a combination of the patient's history, the results of a screening questionnaire, and overnight testing in a sleep laboratory. The screening questionnaire that is used most commonly is the Epworth Sleepiness Scale, or ESS, which was developed in Australia in the early 1990s. The patient may also be asked to keep a sleep diary for one or two weeks and wear a device called an actigraph. The actigraph resembles a wrist watch and measures the person's sleep.

The patient will usually be tested overnight in a medical center equipped with a polysomnograph. The polysomnograph is a machine that measures the electrical activity of the heart and brain, breathing, and eye movement while the patient is sleeping. Another sleep test is called the multiple sleep latency test or MSLT. The patient is given a chance to sleep every two hours during normal waking time. Observations are made of the time taken to reach various stages of sleep. The MSLT

measures the degree of the patient's daytime sleepiness and also detects how soon REM sleep begins.

Treatment

Treatment of narcolepsy involves a combination of medications, lifestyle changes, and psychotherapy. The most common medications given are stimulants that resemble amphetamine. It is important for persons taking stimulants to notify their employer, because the drugs may show up during pre-employment urine tests. Another type of drug that may be prescribed is a drug called Xyrem, which controls cataplexy and helps patients sleep better at night.

Lifestyle changes that are recommended for patients with narcolepsy include:

• Getting enough sleep at night. Patients are advised to go to bed and get up at the same time every day rather than changing their sleeping schedule frequently.
• Taking scheduled short naps at intervals during waking hours. This practice helps to reduce daytime sleepiness.
• Avoiding the use of alcohol and tobacco. These substances can make it harder to sleep at night.
• Getting regular exercise. Physical exercise four to five hours before bedtime helps many people with narcolepsy sleep better.
• Being careful to avoid driving when tired or sleepy.
• Joining a narcolepsy support group. Finding understanding and support from others with the same disorder is particularly helpful to patients who may have waited years to be diagnosed and suffered the loss of jobs, relationships, or educational opportunities in the meantime.

Prognosis

Narcolepsy cannot be cured but it is not a fatal disease. People with narcolepsy can expect to live normal life spans (barring accidents). They can also expect to lead normally productive and meaningful lives with proper care and periodic consultations with a sleep specialist.

Prevention

There is no way known to prevent narcolepsy.

The Future

New drugs that will help narcoleptic patients remain awake were at the clinical trial stage in late 2008. Some researchers in Germany were experimenting with a nasal spray containing hypocretin that might be beneficial to people with narcolepsy. Another possibility is the use of stem cell transplants to restore the cells in the brain that make hypo-cretin, but that approach will likely take several decades to be successful.

SEE ALSO Restless legs syndrome; Sleep apnea

WORDS TO KNOW

Automatic behavior : Activity that a person with narcolepsy can carry out while partially awake but is not conscious of at the time and cannot recall afterward.

Cataplexy : Sudden loss of tone in the voluntary muscles.

Hypnagogic : Referring to the period of partial alertness on the boundary between sleeping and waking.

Hypocretin : A protein produced by certain brain cells that promotes wakefulness and helps to regulate the sleep/wake cycle. It is also known as orexin.

Non-rapid eye movement (NREM) sleep : The first phase of a sleep cycle, in which there is little or no eye movement.

Rapid eye movement (REM) sleep : The phase of a sleep cycle in which dreaming occurs; it is characterized by rapid eye movements.

Sleep cycle : A period of NREM sleep followed by a shorter phase of REM sleep. Most adults have four to six sleep cycles per night.

For more information

BOOKS

Sutton, Amy L., ed. Sleep Disorders Sourcebook: Basic Consumer Health Information about Sleep and Sleep Disorders. Detroit, MI: Omnigraphics, 2005.

PERIODICALS

Chen, Ingfei. “A Leap Forward, But Hurdles Remain in Narcolepsy.” New York Times, May 10, 2008. Available online at http://health.nytimes.com/ref/health/healthguide/esn-narcolepsy-ess.html (accessed May 21, 2008).

WEB SITES

American Academy of Sleep Medicine (AASM). Fact Sheet: Narcolepsy. Available online in PDF format at http://www.aasmnet.org/Resources/FactSheets/Narcolepsy.pdf (updated 2006; accessed May 21, 2008).

Epworth Sleepiness Scale (ESS). Available online at http://www.narcolepsynetwork.org/do2.php (accessed May 21, 2008). This is the screening questionnaire that has been used since 1991 to evaluate people for narcolepsy.

Narcolepsy Network. Narcolepsy: Frequently Asked Questions. Available online at http://www.narcolepsynetwork.org/faq.php (updated 2003; accessed May 21, 2008).

National Institute of Neurological Disorders and Stroke (NINDS). Narcolepsy Fact Sheet. Available online at http://www.ninds.nih.gov/disorders/narcolepsy/detail_narcolepsy.htm (updated January 11, 2008; accessed May 21, 2008).