What is it?

Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. People with narcolepsy often find it difficult to stay awake for long periods of time, regardless of the circumstances. Narcolepsy can cause serious disruptions in your daily routine.

Contrary to what some people believe, narcolepsy isn't related to depression, seizure disorders, fainting, simple lack of sleep or other conditions that may cause abnormal sleep patterns.

Narcolepsy is a chronic condition for which there's no cure. However, medications and lifestyle changes can help you manage the symptoms. Talking to others — family, friends, employer, teachers — can help you cope with narcolepsy.

Symptoms

Symptoms of narcolepsy may worsen for the first few years, and then continue for life. They include:

• Excessive daytime sleepiness. The primary characteristics of narcolepsy are overwhelming drowsiness and an uncontrollable need to sleep during the day. People with narcolepsy fall asleep without warning, anywhere, anytime. For example, you may suddenly nod off while working or talking with friends. You may sleep for a few minutes or up to a half-hour before awakening and feeling refreshed, but eventually you fall asleep again. You also may experience decreased alertness throughout the day. Excessive daytime sleepiness usually is the first symptom to appear and is often the most troublesome, making it difficult for you to concentrate and function fully.
• Sudden loss of muscle tone. This condition, called cataplexy, can cause a number of physical changes, from slurred speech to complete weakness of most muscles, and may last for a few seconds to a few minutes. Cataplexy is uncontrollable and is often triggered by intense emotions, usually positive ones such as laughter or excitement, but sometimes fear, surprise or anger. For example, your head may droop uncontrollably or your knees may suddenly buckle when you laugh. Some people with narcolepsy experience only one or two episodes of cataplexy a year, while others have numerous episodes daily.
• Sleep paralysis. People with narcolepsy often experience a temporary inability to move or speak while falling asleep or upon waking. These episodes are usually brief — lasting one or two minutes — but can be frightening. You may be aware of the condition and have no difficulty recalling it afterward, even if you had no control over what was happening to you. This sleep paralysis mimics the type of temporary paralysis that normally occurs during rapid eye movement (REM) sleep, the period of sleep during which most dreaming occurs. This temporary immobility during REM sleep may prevent your body from acting out dream activity. Not everyone with sleep paralysis has narcolepsy, however. Many people without narcolepsy experience some episodes of sleep paralysis, especially in young adulthood.
• Hallucinations. These hallucinations, called hypnagogic hallucinations, may occur when falling quickly into REM sleep, as you do when you first fall asleep, or upon waking. Because you may be semi-awake when you begin dreaming, you experience your dreams as reality, and they may be particularly vivid and frightening.

Other characteristics

People with narcolepsy may have other sleep disorders, such as obstructive sleep apnea, in which breathing starts and stops throughout the night, restless legs syndrome and even insomnia. People with narcolepsy may also act out their dreams at night by flailing their arms or kicking and screaming.

Some episodes of sleep attacks are brief, lasting seconds. Some people with narcolepsy experience automatic behavior during these brief episodes. For example, you may fall asleep while performing a task you normally perform, such as writing, typing or driving, and you continue to function while asleep. When you awaken, you can't remember what you did, and you probably didn't do it well. For instance, if you were writing, what you wrote asleep may look like scribbling.

The signs and symptoms of narcolepsy can begin anytime up to your 50s, but they most commonly begin between the ages of 10 and 25. Symptoms often are more severe for those who develop them early in life, rather than in adulthood.

Causes

The exact cause of narcolepsy isn't known. Genetics may play a role. Other factors, such as infection, stress or exposure to toxins, may contribute to the development of narcolepsy.

Normal sleep pattern vs. narcolepsy

The normal process of falling asleep begins with a phase called non-rapid eye movement (NREM) sleep. During this phase, your brain waves slow considerably. After an hour or two of NREM sleep, your brain activity picks up again, and REM sleep begins. Most dreaming occurs during REM sleep.

In narcolepsy, however, you may suddenly enter into REM sleep without first experiencing NREM sleep, both at night and during the day. Some of the characteristics of REM sleep, such as sudden lack of muscle tone, sleep paralysis and vivid dreams, occur during other sleep stages in people with narcolepsy.

The role of brain chemicals

Hypocretin is an important chemical in your brain that helps regulate wakefulness and REM sleep. People with narcolepsy have low levels of this neurochemical in their spinal fluid. It's particularly low in those who experience cataplexy. Exactly what causes the loss of hypocretin-producing cells in the brain isn't known, but experts suspect it's due to an autoimmune reaction.

Complications

Public misunderstanding of the condition

Narcolepsy may cause serious problems for you professionally and personally. Others might see you as lazy, lethargic or rude. Your performance may suffer at school or work.

Interference with intimate relationships

Extreme sleepiness may cause low sex drive or impotence, and people with narcolepsy may even fall asleep while having sex. The problems caused by sexual dysfunction can be further complicated by emotional difficulties. Intense feelings, such as anger or joy, can trigger some signs of narcolepsy such as cataplexy, causing affected people to withdraw from emotional interactions.

Physical harm

Sleep attacks may result in physical harm to people with narcolepsy. You're at increased risk of a car accident if you have an attack while driving. Your risk of cuts and burns is greater if you fall asleep while preparing food.

Diagnosis

Your doctor may make a preliminary diagnosis of narcolepsy based on your excessive daytime sleepiness and sudden loss of muscle tone (cataplexy). After an initial diagnosis, your doctor may refer you to a sleep specialist for more evaluation.

Formal diagnosis may require staying overnight at a sleep centre, where you undergo an in-depth analysis of your sleep by a team of specialists. Methods of diagnosing narcolepsy and determining its severity include:

• Sleep history. Your doctor will ask you for a detailed sleep history. A part of the history involves filling out the Epworth Sleepiness Scale, which uses a series of short questions to gauge your degree of sleepiness. For instance, you indicate on a numbered scale how likely it is that you would doze off in certain situations, such as sitting down after lunch.
• Sleep records. You may be asked to keep a detailed diary of your sleep pattern for a week or two, so your doctor can compare how your sleep pattern and alertness are related. Often, in addition to this sleep log, the doctor will ask you to wear an actigraph. This device has the look and feel of a wristwatch and measures how and when you sleep.
• Polysomnogram. This test measures a variety of signals during sleep using electrodes placed on your scalp. For this test, you must spend a night at a medical facility. The test measures the electrical activity of your brain (electroencephalogram) and heart (electrocardiogram) and the movement of your muscles (electromyogram) and eyes (electro-oculogram). It also monitors your breathing.
• Multiple sleep latency test. This examination measures how long it takes you to fall asleep during the day. You'll be asked to take four or five naps, each nap two hours apart. Specialists will observe your sleep patterns. People who have narcolepsy fall asleep easily and enter into rapid eye movement (REM) sleep quickly.

These tests can also help doctors rule out other possible causes of your signs and symptoms. Other sleep disorders, such as sleep apnea, can cause excessive daytime sleepiness.

Another test your doctor might recommend is a hypocretin test, which measures the levels of hypocretin in the fluid that surrounds your spinal cord. Most people with narcolepsy have low levels of this brain chemical that regulates REM sleep. A sample of your spinal fluid is obtained with a lumbar puncture (spinal tap), during which a needle is inserted into your lower spine to withdraw spinal fluid.

References

http://www.webmd.com/sleep-disorders/guide/narcolepsy

http://www.medicinenet.com/narcolepsy/article.htm

http://emedicine.medscape.com/article/1188433-overview

http://healthysleep.med.harvard.edu/narcolepsy/diagnosing-narcolepsy/narcolepsy-testing