What is Narcolepsy?
Narcolepsy is a sleep disorder in the hypersomnia family. People with narcolepsy may get enough sleep at night and feel rested in the morning, but can fall asleep spontaneously throughout the day. Like other hypersomnias, the main symptom of narcolepsy is excessive daytime sleepiness. In addition, characteristics of narcolepsy include spontaneous “sleep attacks” lasting anywhere from a few seconds to several minutes or longer.
People with narcolepsy may experience changes in normal REM sleep cycles, fragmented sleep, vivid or intense sleep-related hallucinations, and sleep paralysis. Narcolepsy is a neurological disorder with a severe impact on an individual’s ability to function normally and carry out basic daily tasks, including driving and performing job duties.
There are two types of narcolepsy:
Type 1 narcolepsy (or narcolepsy with cataplexy) involves suddenly becoming limp or unable to move while awake (cataplexy). This sudden muscle weakness is often triggered by strong emotions. People with type 1 narcolepsy have excessive daytime sleepiness and may also experience sleep hallucinations and sleep paralysis.
Type 2 narcolepsy (or narcolepsy without cataplexy) is also characterized by excessive daytime sleepiness, but does not feature the sudden loss of muscle tone (cataplexy) or sleep attacks.
Type 1 and type 2 narcolepsy are not caused by another illness or medical condition. Secondary narcolepsy occurs as a result of an injury to the hypothalamus, located deep inside the brain.
How Common is Narcolepsy?
Narcolepsy is relatively rare, affecting an estimated 200,000 people in the United States. The disorder affects males and females equally and often appears in childhood or young adulthood, most commonly between ages 7 and 25.
Symptoms of Narcolepsy
Excessive Daytime Sleepiness. The primary symptom of narcolepsy is EDS, or the urge to go to sleep throughout the day despite sleeping enough at night. In people with narcolepsy, the drive to sleep can be overwhelming.
Cataplexy. Some people with narcolepsy experience sudden limpness or loss of muscle tone, often immediately after strong emotions like happiness, fear, anger or excitement. Cataplexy occurs on a spectrum from mild, involving minor muscle weakness or loss of muscle tone, to severe, in which the entire body suddenly goes limp. Cataplexy resembles the paralysis or inhibition of muscle activity that typically occurs during REM sleep. However, during episodes of cataplexy, the individual is fully awake.
Sleep attacks. Some people with narcolepsy can experience brief “sleep attacks” or episodes of sleep that occur spontaneously. These episodes can last anywhere from a few seconds to several minutes or longer.
Hallucinations. People with narcolepsy may experience dream-like hallucinations while awake. These images can be frightening or intense, and may involve all the body’s senses.
Sleep paralysis. Narcolepsy can sometimes involve the sleep paralysis, the temporary inability to speak or move during transitions between sleep and arousal.
Fragmented sleep. Individuals with narcolepsy may experience arousals during sleep and have difficulty staying asleep at night. These arousals may be caused by periodic leg movements, sleep apnea, or insomnia.
Automatic behaviors. Narcoleptics may experience brief episodes (lasting a few seconds) of spontaneous sleep during routine daily activities like talking, cooking, or driving, and continue performing that activity while asleep. Afterward, the person usually has no memory of the sleep episode.
What Causes Narcolepsy?
Narcolepsy is a neurological disorder caused by abnormalities in brain chemistry. Most people with narcolepsy have lower levels of hypocretin, a brain chemical that promotes wakefulness. People with type 1 narcolepsy (or narcolepsy with cataplexy) have especially low levels of hypocretin.
This deficit in hypocretin may have several causes:
- Fewer hypocretin-producing neurons in the brain. Hypocretin (also called orexin) is a neuropeptide involved in sleep-wake regulation and appetite. In people with narcolepsy, the neurons that produce hypocretin may be missing or damaged.
- An autoimmune disorder. Researchers believe that narcolepsy, particularly type 1 narcolepsy, may be caused when the body’s immune system attacks hypocretin-producing neurons in the brain.
- Family history. Though narcolepsy most often occurs spontaneously, without family history, as many as 10 percent of narcoleptics have an immediate family member with similar symptoms. Mutations in a gene (hypocretin receptor 2 gene or Hcrtr 2) can cause familial narcolepsy in dogs.
- Brain injuries. In rare cases, trauma to the hypothalamus region of the brain, involved in regulating sleep, may cause narcolepsy. Brain tumors or lesions in this brain region may play a role as well.
Diagnosis of Narcolepsy
The diagnosis of narcolepsy begins with a comprehensive medical evaluation to rule out other medical conditions that may cause excessive daytime sleepiness. Patients may be asked to keep a sleep journal to track sleep patterns for several weeks.
The next step in diagnosing narcolepsy is evaluating sleep abnormalities using one or more diagnostic tools:
- A polysomnogram, or overnight sleep study, allows clinicians to evaluate heart, brain and lung activity during sleep. This test can help determine whether REM sleep cycles fit the characteristics of narcolepsy. In people with narcolepsy, REM sleep generally begins within 15 minutes of falling asleep; people without narcolepsy enter REM sleep after 60 to 90 minutes of sleep.
- A multiple sleep latency test is a nap test in which people are asked to take multiple naps over the course of a day. This generally happens the day offer an overnight sleep study. The MSLT can help determine the extent of excessive daytime sleepiness.
- Laboratory tests of spinal fluid can measure the amount of hypocretin present. Low levels of hypocretin almost always indicate narcolepsy.
Narcolepsy is a chronic, lifelong disease. While narcolepsy cannot be cured, symptoms can be managed. Symptoms of narcolepsy can lessen and improve over time.
Narcolepsy treatment drugs include stimulants, antidepressants and sedatives.
Drugs that promote wakefulness may be used to correct primary symptom of narcolepsy, excessive daytime sleepiness. The most common stimulants used to treat narcolepsy are dextroamphetamine, pemoline methamphetamine, and methylphenidate (Ritalin). These are classified as Central Nervous System (CNS) stimulants.
Another medication, Modafinil, is marketed as Provigil and Nuvigil. Modafinil promotes wakefulness with fewer side effects than stimulant medications.
Tricyclic and SSRI antidepressants may be used to treat narcolepsy. These medications generally have fewer side effects and less potential for abuse than stimulants. Sodium oxybate is a strong sedative sometimes prescribed for narcolepsy. This medication is intended to promote more restful sleep at night in order to reduce daytime sleepiness.
The multiple sclerosis drug baclofen may be useful in treating narcolepsy. Baclofen is a GABA agonist and works in a manner similar to sodium oxybate.
In some people with narcolepsy, drug therapies are ineffective. Physicians recommend behavioral changes to help manage narcolepsy symptoms. Behavioral changes can include:
- Taking frequent naps throughout the day
- Maintaining a consistent sleep routine and schedule
- Avoiding alcohol and large meals before bed