Narcolepsy is a neurological condition characterized by irresistible episodes of sleep and general sleep disorder. It is a kind of dyssomnia.
Table of contents |
2 What happens in narcolepsy 3 Causes of narcolepsy 4 Prevalence of narcolepsy 5 Diagnosis 6 Treatment 7 Research 8 External links |
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 sleep attacks may occur with or
without warning and may be irresistible. These attacks can
occur repeatedly in a single day. Drowsiness may persist
for prolonged periods of time. In addition, nighttime sleep
may be fragmented with frequent wakenings.
Three other classic symptoms of narcolepsy, which may not
occur in all patients, are:
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 sleep attacks. 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.
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 muscle tone, sleep
paralysis, and vivid dreams--occur at other times in people
with narcolepsy. For example, the lack of muscle tone 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) REM sleep. This has several consequences:
Narcolepsy may be associated with damage to the amygdala. A gene associated with it in dogs (perhaps one of many) has been identified; it is also more common among certain human genotypes than others.
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 rapid eye movement (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.
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.
Although it is estimated that narcolepsy afflicts as many as
200,000 Americans, 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 major 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 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.
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), methamphetamine or Modafinil. However in many cases, planned regular short naps, can reduce the need for drowsiness treatment to a low or non-existent level. The loss of muscle control is treated using clomipramine, impramine, or protryptiline but this need only be done in severe cases.
In the US the approval of GHB (Xyrem) has added another drug to the armamentum available to physicians. It is thought to be effective because it increases the quality of nocturnal sleep.
Although there is no cure for narcolepsy, treatment options
are available to help reduce the various symptoms.
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.
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.
== How Can Individuals and Their Families and Friends Cope 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:
Symptoms of narcolepsy
Daytime sleepiness, sleep paralysis, and hypnagogic hallucinations can also occur in people who do not have narcolepsy.What happens in narcolepsy
A person with narcolepsy can dream even when they fall asleep for only a few seconds. Causes of narcolepsy
Prevalence of narcolepsy
Diagnosis
Treatment
Research
See also: Orexin