What is Narcolepsy?
Narcolepsy is a chronic neurological disorder caused by the brain's inability to regulate sleep-wake cycles normally. At various times throughout the day, people with narcolepsy experience fleeting urges to sleep. If the urge becomes overwhelming, patients fall asleep for periods lasting from a few seconds to several minutes. In rare cases, some people may remain asleep for an hour or longer.
Narcoleptic sleep episodes can occur at any time, and thus frequently prove profoundly disabling. People may involuntarily fall asleep while at work or at school, when having a conversation, playing a game, eating a meal, or, most dangerously, when driving an automobile or operating other types of potentially hazardous machinery. In addition to daytime sleepiness, three other major symptoms frequently characterize narcolepsy: cataplexy, or the sudden loss of voluntary muscle tone; vivid hallucinations during sleep onset or upon awakening; and brief episodes of total paralysis at the beginning or end of sleep.
Contrary to common beliefs, people with narcolepsy do not spend a substantially greater proportion of their time asleep during a 24-hour period than do normal sleepers. In addition to daytime drowsiness and involuntary sleep episodes, most patients also experience frequent awakenings during nighttime sleep. For these reasons, narcolepsy is considered to be a disorder of the normal boundaries between the sleeping and waking states.
For most adults, a normal night's sleep lasts about 8 hours and is composed of four to six separate sleep cycles. A sleep cycle is defined by a segment of non-rapid eye movement (NREM) sleep followed by a period of rapid eye movement (REM) sleep. The NREM segment can be further divided into stages according to the size and frequency of brain waves. REM sleep, in contrast, is accompanied by bursts of rapid eye movement (hence the acronym REM sleep) along with sharply heightened brain activity and temporary paralysis of the muscles that control posture and body movement. When subjects are awakened from sleep, they report that they were "having a dream" more often if they had been in REM sleep than if they had been in NREM sleep. Transitions from NREM to REM sleep are governed by interactions among groups of neurons (nerve cells) in certain parts of the brain.
Scientists now believe that narcolepsy results from disease processes affecting brain mechanisms that regulate REM sleep. For normal sleepers a typical sleep cycle is about 100 - 110 minutes long, beginning with NREM sleep and transitioning to REM sleep after 80 - 100 minutes. But, people with narcolepsy frequently enter REM sleep within a few minutes of falling asleep.
Who Gets Narcolepsy?
Narcolepsy is not rare, but it is an underrecognized and underdiagnosed condition. The disorder is estimated to affect about one in every 2,000 Americans. But the exact prevalence rate remains uncerntain, and the disorder may affect a larger segment of the population.
Narcolepsy appears throughout the world in every racial and ethnic group, affecting males and females equally. But prevalence rates vary among populations. Compared to the U.S. population, for example, the prevalence rate is substantially lower in Israel (about one per 500,000) and considerably higher in Japan (about one per 600).
Most cases of narcolepsy are sporadic-that is, the disorder occurs independently in individuals without strong evidence of being inherited. But familial clusters are known to occur. Up to 10 percent of patients diagnosed with narcolepsy with cataplexy report having a close relative with the same symptoms. Genetic factors alone are not sufficient to cause narcolepsy. Other factors-such as Infection, immune-system dysfunction, trauma, hormonal changes, Stress-may also be present before the disease develops. Thus, while close relatives of people with narcolepsy have a statistically higher risk of developing the disorder than do members of the general population, that risk remains low in comparison to diseases that are purely genetic in origin.
* Obstructive sleep apnea is a temporary cessation of breathing that occurs repeatedly during sleep and is caused by a narrowing of the airway. Restless legs syndrome is a neurological disorder characterized by unpleasant sensations-burning, creeping, tugging-in the legs and an uncontrollable urge to move when at rest
