What is narcolepsy?

Narcolepsy is a malfunction of the sleep/wake regulating system in the brain which until recently was of unknown origin. Its most common manifestation is Excessive Daytime Sleepiness and sleep attacks.

The other conspicuous symptom is a sudden loss of muscular control triggered by amusement, anger or excitement which is called cataplexy.

Other symptoms of narcolepsy are:

  • Temporary paralysis on falling asleep or awakening (sleep paralysis). The periods of paralysis are usually brief - a few minutes - but can persist for up to 30 minutes. Episodes of sleep paralysis may alarm patients, particularly those who experience the sensation of being unable to breathe.
  • Hallucinations - vivid images or sounds - on falling asleep or awakening (Hypnagogic and hypnopompic hallucinations respectively). These hallucinations frequently combine elements of dream sleep and consciousness and are often very disturbing to patients.
  • Moments (but sometimes extended periods) of trance-like behaviour in which routine activities are continued on 'auto-pilot' (Automatic behaviour).
  • Interruption of night-time sleep by frequent waking periods, marked by quickening of the heart rate, over-alertness, hot flushes, and agitation. This disturbed sleep can contribute to a feeling of tiredness in the morning.

The condition appears to be associated with faulty control of a phase of sleep called Rapid Eye Movement (REM) Sleep.  REM sleep is associated with profound brain activity, dreaming and loss of muscle tone.  In people who do not have narcolepsy REM sleep does not normally start until sleep has been underway for about an hour or so. Following the first occurrence of REM sleep sleep reverts back to non-REM sleep.  REM sleep then re-occurs at approximately 90 minute intervals. However, in people with narcolepsy REM sleep starts very quickly - even at the start of sleep.  This results in quite marked symptoms when falling asleep and a loss of muscle tone. Some people with narcolepsy even have 'intrusion' of some of the signs of REM sleep into their waking moments.

The concept of narcolepsy as being a disease of REM sleep may be too simplistic and does not explain the daytime sleepiness associated with the condition.  As stated above, most probably, narcolepsy results from the disruption of the mechanisms controlling both sleep and wakefulness. This would explain why, in people with narcolepsy, night-time sleep is very fragmented - even to the point of producing insomnia, and they cannot stay awake for prolonged periods.

Narcolepsy usually begins in adolescence but instances of onset earlier, or as late as middle age, are on record. The type and severity of symptoms vary from person to person and may either improve or worsen with time.

The prevalence of narcolepsy is not accurately known as it is significantly under-reported. However, the reported prevalence of narcolepsy in the population ranges from 5 in 10,000 (0.05%) in Europe and North America, to 16 in 10,000 in Japan.

An inheritable factor has been identified which can increase the likelihood of developing narcolepsy by up to 10 times in persons with the factor compared with those without it. Indeed, there there is a very strong correlation between narcolepsy with cataplexy and this factor - about 90% of those with narcolepsy have it.  However, this factor is also very commonly found in the general population and is thus neither specific nor sensitive for narcolepsy. This factor may be detected by looking for a particular 'tissue type' (HLA DQB1 *0602) in the subjects' blood. This test is regarded as being of little value in confirming or excluding the diagnosis of narcolepsy and may lead to an inappropriate diagnosis.

Narcolepsy is far from being a trivial condition and has a profound effect on well-being.  'Quality of Life' studies have shown the impact of narcolepsy to be as significant as that of Parkinson's disease.