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Diseases » Narcolepsy » Wikipedia
 

Narcolepsy in Wikipedia

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Narcolepsy". (Source - Retrieved 2006-09-07 14:17:20 from https://en.wikipedia.org/wiki/Narcolepsy)

Introduction

Narcolepsy is a neurological condition most characterized by Excessive Daytime Sleepiness (EDS), episodes of sleep and disorder of REM or rapid eye movement sleep. It is a kind of dyssomnia.

Symptoms of narcolepsy

The main characteristic of narcolepsy is overwhelming excessive daytime sleepiness (EDS), even after adequate nighttime sleep. A person with narcolepsy is likely to become drowsy or to fall asleep, often at inappropriate times and places. Daytime naps may occur with or without warning and may be irresistible. These naps can occur several times a day. They are typically refreshing, but only for up to a couple hours. Drowsiness may persist for prolonged periods of time. In addition, night-time sleep may be fragmented with frequent wakenings.

Four other classic symptoms of narcolepsy, which may not occur in all patients, are:

  • Cataplexy: sudden episodes of loss of muscle function, ranging from slight weakness (such as limpness at the neck or knees, sagging facial muscles, or inability to speak clearly) to complete body collapse. Episodes may be triggered by sudden emotional reactions such as laughter, anger, surprise, or fear, and may last from a few seconds to several minutes. The person remains conscious throughout the episode.
  • Sleep paralysis: temporary inability to talk or move when waking up. It may last a few seconds to minutes. Often frightening but not dangerous.
  • Hypnagogic hallucinations: vivid, often frightening, dream-like experiences that occur while dozing, falling asleep and/or while awakening.
  • Automatic behavior: Automatic behavior occurs when a person continues to function (talking, putting things away, etc.) during sleep episodes, but awakens with no memory of performing such activities. It is estimated that up to 40 percent of people with narcolepsy experience automatic behavior during sleep episodes.

Daytime sleepiness, sleep paralysis, and hypnagogic hallucinations also occur in people who do not have narcolepsy, more frequently in people who are suffering from extreme lack of sleep. Cataplexy is generally considered to be unique to narcolepsy.

In most cases, the first symptom of narcolepsy to appear is excessive and overwhelming daytime sleepiness. The other symptoms may begin alone or in combination months or years after the onset of the daytime naps. There are wide variations in the development, severity, and order of appearance of cataplexy, sleep paralysis, and hypnagogic hallucinations in individuals. Only about 20 to 25 percent of people with narcolepsy experience all four symptoms. The excessive daytime sleepiness generally persists throughout life, but sleep paralysis and hypnagogic hallucinations may not.

The symptoms of narcolepsy, especially the excessive daytime sleepiness and cataplexy, often become severe enough to cause serious problems in a person's social, personal, and professional lives and severely limit activities.

What happens in narcolepsy

Normally, when an individual is awake, brain waves show a regular rhythm. When a person first falls asleep, the brain waves become slower and less regular. This sleep state is called non-rapid eye movement (NREM) sleep. After about an hour and a half of NREM sleep, the brain waves begin to show a more active pattern again. This sleep state, called rapid eye movement (REM) sleep, is when most remembered dreaming occurs.

In narcolepsy, the order and length of NREM and REM sleep periods are disturbed, with REM sleep occurring at sleep onset instead of after a period of NREM sleep. Thus, narcolepsy is a disorder in which REM sleep appears at an abnormal time. Also, some of the aspects of REM sleep that normally occur only during sleep -- lack of muscular control, sleep paralysis, and vivid dreams -- occur at other times in people with narcolepsy. For example, the lack of muscular control can occur during wakefulness in a cataplexy episode. Sleep paralysis and vivid dreams can occur while falling asleep or waking up.

Simply put, the brain does not pass through the normal stages of dozing and deep sleep but goes directly into (and out of) rapid eye movement (REM) sleep. This has several consequences:

  • Nighttime sleep does not include much deep sleep, so the brain tries to "catch up" during the day, hence EDS
  • People with narcolepsy fall quickly into what appears to be very deep sleep
  • They wake up suddenly and can be disoriented when they do
  • They have very vivid dreams, which they often remember

People with narcolepsy may dream even when they only fall asleep for a few seconds.

Causes of narcolepsy

While the cause of narcolepsy has not yet been determined, scientists have discovered conditions that may increase an individual's risk of having the disorder. Specifically, there appears to be a strong link between narcoleptic individuals and certain genetic conditions. One factor that may predispose an individual to narcolepsy involves an area of Chromosome 6 known as the HLA complex. There appears to be a correlation between narcoleptic individuals and certain variations in HLA genes, although it is not required for the condition to occur.

Certain variations in the HLA complex are thought to increase the risk of an auto-immune response to protein producing neurons in the brain. The protein produced, called hypocretin or orexin, is responsible for controlling appetite and sleep patterns. Individuals with narcolepsy often have reduced numbers of these protein producing neurons in their brains.

The neural control of normal sleep states and the relationship to narcolepsy are only partially understood. In humans, narcoleptic sleep is characterized by a tendency to go abruptly from a waking state to REM sleep with little or no intervening non-REM sleep. The changes in the motor and proprioceptive systems during REM sleep have been studied in both human and animal models. During normal REM sleep, spinal and brainstem alpha motor neuron hypopolarization produces almost complete atonia of skeletal muscles via an inhibitory descending reticulospinal pathway. Acetylcholine may be one of the neurotransmitters involved in this pathway. In narcolepsy, the reflex inhibition of the motor system seen in cataplexy is believed identical to that seen in normal REM sleep.

In 2004 researchers in Australia induced narcolepsy-like symptoms in mice by injecting them with antibodies from narcoleptic humans, the research has been published in the Lancet providing strong evidence suggesting that Narcolepsy might be an autoimmune disease.

Narcolepsy is strongly associated with HLA DQB1*0602 genotype. This may represent linkage disequilibrium.

Despite the experimental evidence in human narcolepsy that there may be an inherited basis for at least some forms of narcolepsy, the mode of inheritance remains unknown.

Prevalence of narcolepsy

It is estimated that there are as many as 3 million people worldwide affected by narcolepsy. In the United States it is estimated that narcolepsy afflicts as many as 200,000 Americans, but fewer than 50,000 are diagnosed. It is as widespread as Parkinson's disease or multiple sclerosis and more prevalent than cystic fibrosis, but it is less well known. Narcolepsy is often mistaken for depression, epilepsy, or the side effects of medications.

Narcolepsy can occur in both men and women at any age, although its symptoms are usually first noticed in teenagers or young adults. There is strong evidence that narcolepsy may run in families; 8 to 12 percent of people with narcolepsy have a close relative with the disease.

Narcolepsy has its typical onset in adolescence and young adulthood. There is an average 15-year delay between onset and correct diagnosis, that may contribute substantially to the disabling features of the disorder. Cognitive, educational, occupational, and psychosocial problems associated with the excessive daytime sleepiness of narcolepsy have been documented. For these to occur in the crucial teen years when education, development of self-image, and development of occupational choice are taking place is especially damaging. While cognitive impairment does occur; it may only be a reflection of the excessive daytime somnolence.

The prevalence of narcolepsy in the United States has been estimated to be as high as one per 1,000. It is a reason for patient visits to sleep disorder centers, and with its onset in adolescence, it is also a major cause of learning difficulty and absenteeism from school. Normal teenagers often already experience excessive daytime sleepiness because of a maturational increase in physiological sleep tendency accentuated by multiple educational and social pressures; this may be disabling with the addition of narcolepsy symptoms in susceptible teenagers. In clinical practice, the differentiation between narcolepsy and other conditions characterized by excessive somnolence may be difficult. Treatment options are currently limited. There is a paucity in the literature of controlled double-blind studies of possible effective drugs or other forms of therapy. Mechanisms of action of some of the few available therapeutic agents have been explored but detailed studies of mechanisms of action are needed before new classes of therapeutic agents can be developed.

Narcolepsy is much more common among men than among women. It is an underdiagnosed condition in the general population. This is partly because its severity varies from obvious down to barely noticeable. Some narcoleptics do not suffer from loss of muscle control. Others may only feel sleepy in the evenings.

Diagnosis

Diagnosis is relatively easy when all the symptoms of narcolepsy are present. But if the sleep attacks are isolated and cataplexy is mild or absent, diagnosis is more difficult.

Two tests that are commonly used in diagnosing narcolepsy are the polysomnogram and the multiple sleep latency test. These tests are usually performed by a sleep specialist. The polysomnogram involves continuous recording of sleep brain waves and a number of nerve and muscle functions during nighttime sleep. When tested, people with narcolepsy fall asleep rapidly, enter REM sleep early, and may awaken often during the night. The polysomnogram also helps to detect other possible sleep disorders that could cause daytime sleepiness.

For the multiple sleep latency test, a person is given a chance to sleep every 2 hours during normal wake times. Observations are made of the time taken to reach various stages of sleep. This test measures the degree of daytime sleepiness and also detects how soon REM sleep begins. Again, people with narcolepsy fall asleep rapidly and enter REM sleep early.

Treatment

Several treatments are available for narcolepsy. These treat the symptoms, not the underlying cause. The drowsiness is normally treated using stimulants such as methylphenidate (Ritalin®), amphetamines (Adderall®), dextroamphetamine (Dexedrine®), methamphetamine (Desoxyn®), modafinil (Provigil®), etc. Other medications used are codeine (see references to clinical studies) and selegiline. In many cases, planned regular short naps can reduce the need for pharmacological treatment of the EDS to a low or non-existent level. The cataplexy is treated using clomipramine, imipramine, or protriptyline but this need only be done in severe cases. A new medication is gamma-hydroxybutyrate (GHB) (Xyrem®), recently approved in the USA by the Food and Drug Administration. It is thought to be effective because it increases the quality of nocturnal sleep.

Treatment is individualized depending on the severity of the symptoms, and it may take weeks or months for an optimal regimen to be worked out. Complete control of sleepiness and cataplexy is rarely possible. Treatment is primarily by medications, but lifestyle changes are also important. The main treatment of excessive daytime sleepiness in narcolepsy is with a group of drugs called central nervous system stimulants. For cataplexy and other REM-sleep symptoms, antidepressant medications and other drugs that suppress REM sleep are prescribed. Caffeine and over-the-counter drugs have not been shown to be effective and are not recommended.

In addition to drug therapy, an important part of treatment is scheduling short naps (10 to 15 minutes) two to three times per day to help control excessive daytime sleepiness and help the person stay as alert as possible. Daytime naps are not a replacement for nighttime sleep.

Ongoing communication among the physician, the person with narcolepsy, and family members about the response to treatment is necessary to achieve and maintain the best control.

Research

Studies supported by the National Institutes of Health (NIH) are trying to increase understanding of what causes narcolepsy and improve physicians' ability to detect and treat the disease. Scientists are studying narcolepsy patients and families, looking for clues to the causes, course, and effective treatment of this sleep disorder.

Recent discovery of families of dogs that are naturally afflicted with narcolepsy has been of great help in these studies. Some of the specific questions being addressed in NIH-supported studies are the nature of genetic and environmental factors that might combine to cause narcolepsy and the immunological, biochemical, physiological, and neuromuscular disturbances associated with narcolepsy.

Scientists are also working to better understand sleep mechanisms and the physical and psychological effects of sleep deprivation and to develop better ways of measuring sleepiness and cataplexy.

Examples of areas of potential research include studies on the pathophysiology of narcolepsy; abnormalities of circadian rhythms, particularly anatomical and biochemical substrates; the molecular genetics of narcolepsy; and the development of new therapies. New, more sensitive, and specific objective diagnostic procedures need to be developed and validated.

While studies in the naturally occurring narcoleptic dog model suggest an autosomal recessive mode of transmission in that model, genetic analysis of cohorts of narcoleptic patients and identification of informative families are needed to define the mode of inheritance and to facilitate the search for gene markers.

Coping with narcolepsy

Learning as much about narcolepsy as possible and finding a support system can help patients and families deal with the practical and emotional effects of the disease, possible occupational limitations, and situations that might cause injury. A variety of educational and other materials are available from sleep medicine or narcolepsy organizations.

Support groups exist to help persons with narcolepsy and their families.

Individuals with narcolepsy, their families, friends, and potential employers should know that:

  • Narcolepsy is a life-long condition that requires continuous medication.
  • Although there is no cure for narcolepsy at present, several medications can help reduce its symptoms.
  • People with narcolepsy can lead productive lives if they are provided with proper medical care.
  • If possible, individuals with narcolepsy should avoid jobs that require driving long distances or handling hazardous equipment or that require alertness for lengthy periods.
  • Parents, teachers, spouses, and employers should be aware of the symptoms of narcolepsy. This will help them avoid the mistake of confusing the person's behavior with laziness, hostility, rejection, or lack of interest and motivation. It will also help them provide essential support and cooperation.
  • Employers can promote better working opportunities for individuals with narcolepsy by permitting special work schedules and nap breaks.

Doctors generally agree that lifestyle changes can be very helpful to those suffering with narcolepsy. Suggested self-care tips, from the National Sleep Foundation, University at Buffalo, and Mayo Clinic, include:

  • Take several short daily naps (10-15 minutes) to combat excessive sleepiness and sleep attacks.
  • Develop a routine sleep schedule – try to go to sleep and awaken at the same time every day.
  • Alert your employers, coworkers and friends in the hope that others will accommodate your condition and help when needed.
  • Do not drive or operate dangerous equipment if you are sleepy. Take a nap before driving if possible. Consider taking a break for a nap during a long driving trip.
  • Join a support group.
  • Break up larger tasks into small pieces and focusing on one small thing at a time.
  • Stand whenever possible.
  • Take several short walks during the day.
  • Carry a tape recorder, if possible, to record important conversations and meetings.

See also

References

  • Smith, et al., A J (June 2004). "A functional autoantibody in narcolepsy". Lancet: 2122-2124.
 

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