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What is narcolepsy?

Narcolepsy is a chronic disease of the Central Nervous System. Its cause is not fully understood and it cannot be cured. However, there are now various treatments that make it possible in many patients to live a more normal life. Narcolepsy is a persistent sleep disorder thought to be associated with a disturbance of the sleep regulating system in the brain. Excessive Daytime Sleepiness is the main symptom and is present in 100% of patients with narcolepsy. Some People with narcolepsy tend to become drowsy or fall asleep without warning at inappropriate times, such as at work, or when eating or driving, and this can lead to dangerous accidents. It can also have a severe impact on their ability to live a normal life, and may lead to job loss, educational or emotional problems such as depression.

Narcolepsy affects men and women. It most often starts in the age range 15-25 years, although it may appear at younger or older ages. It is a life-long condition and no curative treatment is known yet.

What causes narcolepsy?

Narcolepsy is a sleep disorder with an underlying cause that is related to how the brain regulates sleep and wakefulness. It is clearly a physical disease, and not a mental one. The mechanisms of sleep regulation in the brain are extremely complex and are only partially understood. It is clear, however, that different areas of the brain regulate different kinds of sleep.
Recently, a team at the Stanford Centre for Narcolepsy have studied hypocretin (also known as orexin) - a newly discovered chemical transmitter in the brain. They suggested that narcoleptic dogs do not respond normally to the release of the hypocretin in the brain.
Another team, from the University of Texas, has shown that, in mice, a disturbance of the hypocretin system leads to the animals developing symptoms of narcolepsy.

Hypocretin is found mainly in a part of the brain known as the anterior hypothalamus, an area known to play an important role in regulating sleep. Currently, this is the subject of intense research.

What are the symptoms of narcolepsy?

Excessive sleepiness
Excessive sleepiness is usually the first symptom of narcolepsy to develop.

Cataplexy
This is exclusive to narcolepsy and is a sudden loss of muscular control, ranging from slight weakness (such as a drooping jaw) to total collapse, and lasting for a few seconds to a few minutes, during which the person is awake and aware of what is happening. It is usually triggered by strong emotions, such as laughter, fear, anger, or surprise.

Sleep paralysis
This involves being unable to talk or move for up to several minutes while falling asleep or waking up. It tends to disappear if the person is touched.

Hallucinations
Vivid images or sounds that occur when falling asleep or upon waking respectively. Such hallucinations, which appear very real, may be confused with symptoms of mental illness.

Other symptoms
The four symptoms described above are the "classic" symptoms of narcolepsy, but do not always occur together. Other symptoms may also occur, including: automatic behaviours (carrying on routine tasks as if in a trance), disturbed night-time sleep, double vision, and memory and concentration problems.

How is narcolepsy recognised?
Not all people with narcolepsy show all four of the "classical" symptoms, and diagnosis may require specific tests as well as verbal history-taking and examination.
The main tests used (carried out in a specialist sleep laboratory or clinic) are:

Overnight polysomnogram
This painless procedure, in which brain, muscle, eye and heart activity is recorded throughout the night using recording electrodes, shows whether there is disruption to the normal characteristic stages of sleep. It also enables measurement of the total time asleep and the number of awakenings and sleep disturbances during the night. Normal sleep onset passes through four well recognised stages, and dreaming occurs (in a fifth stage, called "rapid eye movement" or REM sleep) after about 90 minutes. In narcolepsy, REM sleep frequently occurs near sleep onset - a phenomenon called Sleep-Onset REM or SOREM. There may also be repeated awakenings during the night.

Multiple Sleep Latency Test (MSLT)
This test of daytime sleepiness is usually carried out the day after polysomnography. The subject (wearing recording electrodes) is asked to lie down in a comfortable, darkened, sound-proof bedroom and attempt to fall asleep. The time taken to fall asleep (sleep latency) and the presence of SOREM sleep are recorded over a 20-minute period, before waking the patient again. The test is usually repeated four or five times, at 2-hourly intervals. Normal sleepers usually take 10-20 minutes to fall asleep, but more than 80% of those with narcolepsy have a mean sleep latency of less than five minutes. In addition, SOREM periods are also common during the MSLT.

Tissue-type testing
Since most cases of narcolepsy are associated with a certain tissue type (HLA DR2 DQw1), many doctors will test for this to help reach a diagnosis. This test involves taking of a small blood sample from the patient.

Dr. Bruno Baconnet
Senior Director
Medical Affairs
Cephalon Europe
(08/04/11)