sections include: causes and mechanisms, diagnosis and treatment
The most visible symptom of narcolepsy is daytime sleepiness. We all feel sleepy sometimes, of course. But people with narcolepsy can suffer frequent and overwhelming sleep attacks, forcing them to nap often during the day. They or their families may interpret this pattern as indicating fatigue or depression. Such sleepiness can cause people great trouble at school or work and is usually what brings them to their doctors.
Narcolepsy’s other prominent symptom is cataplexy, a brief and sudden loss of muscle strength triggered by strong emotions. It is very important in diagnosing narcolepsy because it does not show up in any other disorder; however, not all narcoleptics experience cataplexy. Typically, people feel weak in the knees and have to sit down when they are emotionally excited. Any strong emotion can cause this reaction, from laughing at a funny joke to getting angry. Other attacks of muscle weakness may affect the head (head dropping), jaw (jaw dropping), face, or arms. Cataplexy is frequently mild. It may occur only a few times per month or several times a day. Strong attacks may escalate to complete body paralysis lasting a few minutes. Cataplexy may be confused with epilepsy or other neurological and psychiatric problems, but people remain awake and conscious during cataplexy. Cataplexy can also be confused with catalepsy, a symptom characterized by increased muscle tone and body rigidity, most often in the context of schizophrenia.
Other symptoms of narcolepsy include sleep paralysis, hypnagogic hallucinations, and insomnia. But people with other sleep disorders can have these experiences, too, as do normal individuals on occasion. Sleep paralysis is an inability to move when waking up or falling asleep; the first episode is often frightening, but the feeling always ends after a few seconds or a few minutes. Hypnagogic hallucinations (hypnagogic means “when falling asleep”) are dreamlike visions or perceptions of noise that occur when patients are tired or actually falling asleep. People with vivid dreamlike hallucinations have occasionally been misdiagnosed as schizophrenic.
Contrary to popular belief, people with narcolepsy do not typically sleep more than others. Rather, they fall asleep easily many times during the day and night but have great difficulties staying asleep at night. In other words, they are unable to stay either awake or asleep for long periods of time. Insomnia is thus common for people with narcolepsy. But their total amount of sleep across the 24-hour day is usually normal.
As you would guess, a child who easily falls asleep at school often has trouble following the lessons and receives little sympathy from teachers who do not realize the true problem. Falling asleep on the job is equally troublesome. Less careful observers might assume a narcoleptic has been drinking or taking drugs. Narcolepsy can thus be socially isolating. Unfortunately, it usually takes many years for the disorder to be diagnosed—14 years from onset is the typical lag. Early detection and treatment can help children receive appropriate schooling and adults function more normally in their daily lives.
Causes and Mechanisms
Narcolepsy typically starts when a person is between 15 and 25 years of age, but it may affect children before puberty and older adults as well. Once established, it is a lifelong condition; genuine remissions are exceptional. In the West, approximately 1 person in every 2,000 has narcolepsy with cataplexy, and many more may have narcolepsy without cataplexy. Most cases of narcolepsy are nonfamilial, but first-degree relatives (parents, children, and siblings) of people diagnosed with the disease have 20 to 40 times the risk of developing it.
Many of the symptoms of narcolepsy are due to abnormal transitions from wakefulness to rapid eye movement (REM) sleep. Normally people enter REM sleep 90 to 120 minutes after they fall asleep and return to that state periodically all through the night. Normal REM sleep is associated with vivid dreaming, rapid eye movements, and complete muscle paralysis. It normally occurs in the middle of the night. People with narcolepsy experience abrupt transitions from wakefulness to REM sleep, often before they are completely asleep. This problem produces “dissociated” states in which a person is half awake and half in REM sleep. For example, in sleep paralysis a person is conscious, but his or her muscles are still paralyzed. In hypnagogic hallucinations a person is awake but dreaming as if in REM sleep. Cataplexy is considered similar to REM sleep paralysis but occurs when the brain is excited by an emotion.
Narcolepsy-cataplexy is most often due to a lack of the brain hormone called hypocretin, or orexin. The hormone is synthesized by approximately 20,000 cells in the hypothalamus that help control sleep. Most narcoleptics have lost these cells, so their sleep is not normally regulated. How these crucial cells have been destroyed is still unknown, but most researchers believe an abnormal immune response is involved. In other words, people’s immune systems have mistakenly attacked cells in their own brains. If this hypothesis is confirmed, narcolepsy will be classified as an autoimmune disorder like multiple sclerosis or juvenile-onset diabetes mellitus.
Diagnosis and Treatment
The diagnosis of narcolepsy is usually made by sleep specialists, generally neurologists in a sleep laboratory. If you are seeking such an evaluation, look for laboratories accredited by the American Academy of Sleep Medicine and physicians board certified in sleep medicine; they usually have more experience with the condition. After listening to a person’s experiences, a specialist arranges for him or her to sleep in the lab for a night. Observing sleep can exclude the possibility of sleep apnea and other sleep disorders.
The next day the specialist performs a multiple sleep latency test. This starts with asking the patient to nap four to five times for 20 minutes every two hours. The doctor measures how fast the person falls asleep and notes the presence or absence of REM sleep, using scalp electrodes. Normal individuals either do not fall asleep in these short periods or sleep for a long time, though not long enough to enter REM sleep. In contrast, people with narcolepsy generally fall asleep for short periods and often experience REM sleep in these short naps. The criteria for diagnosing narcolepsy are naps that occur on average less than eight minutes, with two or more REM episodes occurring in the four or five naps.
Physicians may also run a test to look for the human leukocyte antigen (HLA) in a person’s blood, searching for specific types. HLA is only weakly predictive of narcolepsy, however. Another possible test is a lumbar puncture (spinal tap) to measure hypocretin levels in the person’s cerebrospinal fluid (CSF); the result of this test demonstrates narcolepsy very specifically, but it is more invasive and uncomfortable, and doctors usually perform it only when they are doing research on the disorder.
Some people with narcolepsy find their conditions improve when they make changes in their lifestyle, such as napping on schedule and avoiding specific foods. These steps are rarely enough to control the problem, however. Most patients are prescribed medications for their symptoms:
- stimulants (modafinil and amphetamines) for sleepiness
- antidepressant compounds for cataplexy, sleep paralysis, and hypnagogic hallucinations
- sleep-inducing agents for insomnia
These medications help control the symptoms of narcolepsy but do not treat the cause of the disease. They have many side effects and are often only partially effective. Support groups such as the Narcolepsy Network are very helpful for people dealing with the condition.
New treatments aimed at replacing the missing hypocretin hormone are being developed and will probably become very effective. Additionally, researchers are exploring the destruction of the hypocretin-containing cells in the brain. We must understand this process before we can truly prevent or cure narcolepsy.
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