November 27, 2015
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Narcolepsy (cont.)

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What is narcolepsy?

Narcolepsy is a chronic disease of the central nervous system. Excessive daytime sleepiness (EDS) is the main symptom and is present in 100% of patients with narcolepsy. Other primary symptoms of narcolepsy include:

  • loss of muscle tone (cataplexy),
  • distorted perceptions (hypnagogic hallucinations), and
  • inability to move or talk (sleep paralysis).

Additional symptoms include disturbed nocturnal sleep and automatic behavior (patients carry out certain actions without conscious awareness). A 2014 study in the Journal of Sleep Medicine also reported that nightmares may be more prevalent in people with narcolepsy than in the general population. All the symptoms of narcolepsy may be present in various combinations and degrees of severity.

Narcolepsy usually begins in teenagers or young adults and affects both sexes equally. The first symptom of narcolepsy to appear is excessive daytime sleepiness, which may remain unrecognized for a long time in that it develops gradually over time. The other symptoms can follow excessive daytime sleepiness by months or years. Cataplexy may appear before symptoms of narcolepsy.

How common is narcolepsy?

The prevalence of narcolepsy is similar to that of Parkinson's disease and multiple sclerosis. In the United States, the National Institute of Neurological Disorders and Stroke estimates narcolepsy affects one in every 3,000 people.

Narcolepsy often remains undiagnosed or misdiagnosed for several years. This may occur because physicians do not consider the diagnosis of narcolepsy frequently enough. They may think of narcolepsy only in people who have the main symptom of excessive daytime sleepiness. Narcolepsy may not be considered in the evaluation of patients who come to doctors complaining of fatigue, tiredness, or problems with concentration, attention, memory, and performance, and other illnesses (seizures, mental illness, etc.)

What causes narcolepsy?

Advances have been made in the last few years in determining the cause of narcolepsy. The newest discovery has been the finding of abnormalities in the structure and function of a particular group of nerve cells, called hypocretin neurons, in the brains of patients with narcolepsy. These cells are located in a part of the brain called the hypothalamus and they normally secrete neurotransmitter substances (chemicals released by nerve cells to transmit messages to other cells) called hypocretins.

Abnormalities in the hypocretin system may be responsible for the daytime sleepiness and abnormal REM sleep found in narcolepsy. (See the section below on sleep laboratory tests for a discussion of REM sleep.)

Experiments in dogs and mice with narcolepsy suggest an abnormal hypocretin system as a cause for the development of their narcolepsy. People with narcolepsy have been found to have a markedly decreased number of hypocretin nerve cells in the brain. They also have a decreased level of hypocretins in the cerebrospinal fluid (the fluid that surrounds the brain and the spinal cord).

Narcolepsy is associated with a specific type of human leukocyte antigen (HLA). HLAs are genetically determined proteins on the surface of white blood cells. They are a part of the body's immune (defense) system. The finding of a very high HLA- association in narcolepsy led to the proposal that narcolepsy is an autoimmune disease, similar to other HLA-associated diseases such as multiple sclerosis and ankylosing spondylitis.

It is theorized that an autoimmune reaction causes the loss of nerve cells in the brain in patients with narcolepsy. The environment (for example, infection or trauma) might trigger an autoimmune reaction where normal brain cells are attacked by the body's own immune system. As a result, the neurons are damaged and ultimately destroyed, and they and their neurotransmitter chemicals disappear. Whether narcolepsy is an autoimmune disease remains to be proven.

The role of heredity in humans with narcolepsy is not completely understood. No consistent pattern of heredity has been recognized in families so far. It is estimated that relatives of patients with narcolepsy may have a higher predisposition to develop narcolepsy or sleep-related abnormalities, such as increased daytime sleepiness, increased REM sleep, or others. In dogs with narcolepsy, the disease is inherited in a predictable pattern. In these animals, the narcolepsy is caused by a mutation in a particular gene that is normally responsible for producing a receptor (binder) in the brain for the hypocretin neurotransmitter.

What are the symptoms of narcolepsy?

Symptoms of narcolepsy include (each of these are discussed in detail):

  • excessive daytime sleepiness
  • cataplexy
  • hypnagogic hallucinations
  • sleep paralysis
  • disturbed nocturnal sleep
  • automatic behavior
  • other complaints such as blurred vision, double vision, or droopy eyelids

Excessive daytime sleepiness (EDS)

The main symptom of narcolepsy, excessive daytime sleepiness (EDS), causes the patient to tend to fall asleep easily. This can happen in relaxed situations and also at inappropriate times and places. Patients may fall asleep while watching TV, reading a book, driving, attending a meeting, or engaging in a conversation. The daytime sleepiness is present even after normal nighttime sleep. Patients may describe this symptom as being tired, fatigued, sleepy, feeling lazy, or having low energy.

Excessive daytime sleepiness is present throughout the day but the patient, with extreme effort, may be able to resist the sleepiness for some time. Finally, it becomes overwhelming and results in a sleep episode of varied duration (seconds to minutes). In addition to daytime sleepiness, repetitive, irresistible, and unintentional, sudden attacks of sleep may occur throughout the day. Excessive daytime sleepiness usually impairs a patient's functioning because it reduces motivation and vigilance, interferes with concentration and memory, and increases irritability.


Cataplexy is a sudden, temporary loss of muscle control in a person with narcolepsy. An attack of cataplexy usually is triggered by strong emotional reactions such as laughter, excitement, surprise, or anger. Factors that contribute to the attacks of cataplexy include physical fatigue, stress, and sleepiness.

Severe attacks of cataplexy may result in a complete physical collapse with a fall to the ground and risk of injury. Milder forms of cataplexy are more common. These involve regional muscle groups and result in symptoms such as a drooping head, sagging jaw, slurred speech, buckling of the knees, or weakness in the arms. This muscle weakness can be quite subtle. The patient is conscious but usually unable to speak.

Cataplectic attacks may last from a few seconds to several minutes. They may vary from a few per year to numerous attacks per day that could disable the patient. Cataplexy is present in nearly 75% of patients with narcolepsy, according to the National Institutes of Health. The onset of cataplexy may coincide with the onset of excessive daytime sleepiness, but cataplexy often develops years later, so the absence of cataplexy should not rule out the diagnosis of narcolepsy.

Other symptoms may seem unrelated, but may accompany cataplexy. A study in the American Academy of Sleep Medicine also found that nearly one-quarter of patients with narcolepsy/cataplexy reported binge eating at least twice a week.

Medically Reviewed by a Doctor on 9/25/2015


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