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Narcolepsy
ICD-10 G47.4
ICD-9 347
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DiseasesDB {{{DiseasesDB}}}
MedlinePlus {{{MedlinePlus}}}
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MeSH {{{MeshNumber}}}

Narcolepsy (aka hypnolepsy) is a neurological condition characterized by severe fatigue, irresistible episodes of sleep and general sleep disorder. It is a kind of dyssomnia.

Symptoms of narcolepsy Edit

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. Drowsiness may persist for prolonged periods of time. In addition, night-time sleep may be fragmented with frequent wakenings.

Three 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.
    Narcoleptic Minute 006 0001

    A narcoleptic teenager waiting for cataplexy to pass

  • Sleep paralysis: temporary inability to talk or move when falling asleep or waking up. It may last a few seconds to minutes.
  • Hypnagogic hallucinations: vivid, often frightening, dream-like experiences that occur while dozing, falling asleep and/or while awakening.

Daytime sleepiness, cataplexy, 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.

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 disruptions in a person's social, personal, and professional lives and severely limit activities.

What happens in narcolepsy Edit

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, even though the person is in deep sleep. This sleep state, called rapid eye movement (REM) sleep, is when 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.

In narcolepsy, 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
  • Narcoleptics 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

Narcoleptics may dream even when they only fall asleep for a few seconds.

Causes Edit

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 depolarization 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.[How to reference and link to summary or text]

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 some cases of narcolepsy might be caused by autoimmune disease.[1]

Narcolepsy is strongly associated with HLA DQB1*0602 genotype.[2] There is also an association with HLA DR2 and HLA DQ1. 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.

Some cases are associated with genetic diseases such as Niemann-Pick disease[3] or Prader-Willi syndrome[4].

Epidemiology Edit


It is estimated that as many as 3 million people worldwide are affected by narcolepsy. In the United States, it is estimated that this condition afflicts as many as 200,000 Americans [How to reference and link to summary or text], 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. It can also be mistaken for poor sleeping habits, recreational drug use, or laziness.

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 this neurologic disorder.

Narcolepsy has its typical onset in adolescence and young adulthood. There is an average 15-year delay between onset and correct diagnosis which 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 is about 1 per 2,000 persons[5]. 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 an underdiagnosed condition in the general population. This is partly because its severity varies from obvious to barely noticeable. Some people with narcolepsy do not suffer from loss of muscle control. Others may only feel sleepy in the evenings.

Diagnosis Edit

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. It is also possible for cataplexy to occur in isolation.

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 (sleep latency). 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 Edit

The drowsiness is normally treated using amphetamine-like stimulants such as methylphenidate, racemic amphetamine, dextroamphetamine, and methamphetamine, or modafinil, a new stimulant with a different pharmacologic mechanism. In Fall 2007 an alert for severe adverse reactions to modafinil was issued by the FDA [1].

Other medications used are codeine[6] and selegiline. Another drug that is used is atomoxetine[7] (Strattera), a non-stimulant and Norepinephrine reuptake inhibitor (NRI), that has little or no abuse potential[8]. In many cases, planned regular short naps can reduce the need for pharmacological treatment of the EDS to a low or non-existent level. Cataplexy is frequently treated with tricyclic antidepressants such as clomipramine, imipramine, or protriptyline. Venlafaxine, a newer antidepressant which blocks the reuptake of serotonin and norepinephrine, has shown usefulness in managing symptoms of cataplexy. Gamma-hydroxybutyrate (GHB), a medication recently approved by the US Food and Drug Administration, is the only medication specifically indicated for cataplexy. Gamma-hydroxybutyrate has also been shown to reduce symptoms of EDS associated with narcolepsy. While the exact mechanism of action is unknown, GHB is thought to improve the quality of nocturnal sleep.

Treatment is tailored to the individual based on symptoms and therapeutic response. The time required to achieve optimal control of symptoms is highly variable, and may take several months or longer. Medication adjustments are also frequently necessary, and complete control of symptoms is seldom possible. While oral medications are the mainstay of formal narcolepsy treatment, 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.

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 between the health care provider, patient, and the patient's family members is important for optimal management of narcolepsy.

Finally, a recent study reported that transplantation of hypocretin neurons into the pontine reticular formation in rats is feasible, indicating the development of alternative therapeutic strategies in addition to pharmacological interventions [9]

Coping with narcolepsy Edit

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 disorder, 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.

To imagine what a person with narcolepsy copes with daily, keep in mind that while many are not sleep-deprived (in the classical sense), a major symptom of narcolepsy is akin to sleep deprivation in a normal person; as a normal person, imagine going years functioning off just 3-4 hours of sleep per night. While lifestyle changes and drug therapy can help largely mitigate many symptoms of narcolepsy, there currently exists no complete and permanent solution, therefore patience, empathy and self-education are excellent coping tools.

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

  • Narcolepsy is a life-long condition that may require 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 with proper medical care and lifestyle changes.
  • A major physiological and physical effect of narcolepsy is roughly akin to the effects of sleep deprivation; such effects can often be controlled and minimized through a combination of lifestyle changes and drug therapy.
  • Individuals with narcolepsy should avoid jobs that require driving long distances or handling hazardous equipment or that require alertness for lengthy periods (especially where the consequences of falling asleep are dangerous to themselves or others).
  • 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, co-workers 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.
  • Take several short walks during the day.
  • Carry a tape recorder, if possible, to record important conversations and meetings.


See also Edit

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