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What Is Narcolepsy?

Excessive Sleepiness May Be Due to Neurologic Condition

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Updated September 19, 2012

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Narcolepsy is a neurologic condition that results in excessive daytime sleepiness and other symptoms due to a failure to regulate the states of sleep and wakefulness. This failure results in abrupt transitions from one state into the other. This may lead to sudden weakness while awake (called cataplexy) or even complete paralysis, as would normally occur to prevent a person from acting out her dreams. Unfortunately, when this occurs at inappropriate times it may cause injury.

Additionally, people with narcolepsy may experience intense hallucinations while transitioning to sleep (called hypnagogic hallucinations) as the brain generates dreams while the narcoleptic remains awake.

Although only one in three people with narcolepsy will have all four symptoms, these four defining features are characteristic of the disorder. Cataplexy is not known to occur in any other disorder, so its presence is very helpful in identifying narcolepsy as the cause of the other symptoms.

How Common is Narcolepsy?

Narcolepsy was first described by the French physician Jean Gelineau in 1880. It is now thought to affect about 1 in 2,000 people. The symptoms of narcolepsy usually begin in the teens or early twenties, but it may rarely first occur in children or even the elderly. It affects men as commonly as women.

There may be some ethnic variation, as it is quite uncommon among Israeli Jews (with a prevalence of only 0.002%) and occurs relatively frequently among the Japanese (with a prevalence of 0.15%). A study of 18,000 people in five European countries found an estimated prevalence of 0.047%.

There may be a genetic component to the disorder as narcolepsy can be more commonly found among relatives of people with the disorder. However, the environment seems to have an important role as well (only 25 percent of identical twins will both have the disorder).

What Causes Narcolepsy?

Narcolepsy appears to occur because of a loss of the chemical hypocretin in an area of the brain called the hypothalamus. The nerve cells (or neurons) in the brain that rely on this chemical regulate sleep and alertness. Hypocretin is thought to promote wakefulness and maintain normal muscle tone, so it makes sense that its loss would lead to the sudden weakness seen in cataplexy.

It is thought that the body's immune system, which typically is responsible for fighting infection, may turn against the hypocretin-containing neurons. In narcoleptics, studies have shown that 85 to 95 percent of these neurons are lost. When these cells are damaged, there are frequent, inappropriate transitions between sleep and wakefulness.

Narcolepsy may also be caused by rare lesions within the brain that result because of tumors, strokes, or other insults.

Diagnosis and Treatment of Narcolepsy

If you believe you may be suffering from narcolepsy, it is important to speak with your doctor and a sleep specialist. After a careful evaluation and examination, you may need to undergo other testing to establish the diagnosis of narcolepsy. In general, these tests will include an overnight sleep study called a polysomnogram and a study the next day called a multiple sleep latency test (MSLT).

In addition, there may be laboratory tests (including a genetic test). If your sleep studies are negative but there is still a strong suspicion for narcolepsy, it may be important to test your cerebrospinal fluid for the chemicals orexin and hypocretin.

There is no cure for narcolepsy, but treatments may help to alleviate some of the symptoms. Excessive daytime sleepiness may be alleviated with stimulants such as Ritalin, Provigil, and Nuvigil. A medication called sodium oxybate can effectively treat the sleepiness as well as cataplexy.

If you have narcolepsy, it is best to review the treatment options with your physician to ensure that the appropriate medication is selected to manage your particular symptoms.

Sources:

American Academy of Sleep Medicine. "International classification of sleep disorders: Diagnostic and coding manual." 2nd ed. 2005.

Culebras, A. "Update on idiopathic narcolepsy and the symptomatic narcolepsies." Rev Neurol Dis 2005;2(4):203-310.

Ohayon, MM, et al. "Prevalence of narcolepsy symptomatology and diagnosis in the European general population." Neurology 2002; 58:1826.

Okun, ML, et al. "Clinical aspects of narcolepsy-cataplexy across ethnic groups." Sleep 2002;25:27.

Thorpy, M.J. "Narcolepsy." Continuum Lifelong Learning Neurol 2007;13(3):101-114.

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