Narcolepsy

Learn About Narcolepsy

Sleep and wakefulness are behaviorally and physiologically distinct states that are inconsistent with each other.  The region of the brain called the hypothalamus is tasked with keeping sleep and wakefulness apart and usually does so well.  However, some people have a condition called narcolepsy in which sleep suddenly intrudes into wakefulness.  These “sleep attacks” occur at random and without warning, and can last from a few seconds to minutes.  In addition to the sleep attacks many with narcolepsy can experience cataplexy, a condition of the sudden loss of muscle tone occurring during wakefulness.  Other symptoms of narcolepsy include hallucinations (usually vivid images) and paralysis upon awakening or falling off to sleep.

Normally sleep is divided into recurrent cycles, each lasting about 90 minutes.  Sleep becomes increasingly deep then sometimes somewhat lighter before terminating into a period of rapid eye movement, or REM, sleep.  REM sleep distinguishes itself from the remainder of the sleep cycle by heightened brain activity with rapid eye movements clearly visible beneath the closed lids.  During this time people are dreaming, although dreaming also occurs, albeit less frequently, during other portions of the cycle.  During REM sleep the dreamer is kept from acting out his dream by a paralysis of the muscles, especially those responsible for volitional movement and the maintenance of postural set.  Normally it takes about 80 minutes into the first sleep cycle before the first REM episode occurs; however, people with narcolepsy frequently enter REM shortly after falling asleep, referred to as “sleep-onset REM.”

People with narcolepsy uniformly experience excessive daytime sleepiness, or EDS.  The Epworth Sleepiness Scale captures this tendency with a numerical score, with higher numbers indicating increased sleepiness.  While high Epworth scores are not specific to narcolepsy, narcolepsy is almost always accompanied by high scores.  The excessive daytime sleepiness can occur in attacks, called sleep attacks, occurring at inopportune and potentially dangerous times of day.  Microsleeps, or brief episodes of sleep can occur in which people are asleep while performing routine, repetitive activity called automatic behaviors.  During such times the patient is in a state of confusional arousal, in which their behaviors are impaired and can rarely be recalled.  Handwriting can deteriorate into an illegible scrawl; speech may become slurred and incoherent; driving becomes erratic or the driver becomes lost; things can be hidden away in unusual places and cannot be found later.  

Unique to narcolepsy is cataplexy, a period of inappropriate paralysis of the muscles of volitional movement and postural set, indicative of the intrusion of REM sleep muscle tone loss into waking.  During attacks of cataplexy people remain fully conscious even as they experience varying degrees of weakness and impaired ability to respond appropriately to environmental stimuli.  Cataplexy can occur spontaneously, but it is more often triggered by sudden, strong emotions such as fear, anger, stress, excitement, or humor.  Interestingly, laughter is reportedly the most common trigger.  A phenomenon related to cataplexy occurs when falling off to sleep or awakening from sleep, in which instance it is referred to as sleep paralysis.  Occurring under the same conditions are hallucinations (usually visual); they are hypnagogic when occurring at sleep onset and hypnopompic when occurring upon awakening.    These conditions, cataplexy, sleep paralysis, and the hypnagogic and hypnopompic hallucinations can be misdiagnosed as seizures or some other neurological condition, or a psychiatric illness.

Narcolepsy likely has multiple causes.  However, most people with narcolepsy have low levels of the neurotransmitter hypocretin (also known as orexin), which promotes wakefulness.  When cataplexy is present, the cause is most often the destruction of the brain cells that produce hypocretin.  It appears that the body’s immune system mistakenly attacks these healthy cells resulting in the cell loss – that is, the process is autoimmune.  Interestingly, hypocretin has been associated with weight loss in animal models, and weight gain, even obesity, is a common problem amongst those with narcolepsy.  It should be noted, however, that other factors resulting in trauma to the brain such as metabolic, hormonal, or dietary stress, especially during vulnerable periods in development such as puberty and menopause, may exercise a causative role in the genesis of the disease.  

Essential in confirming a diagnosis of narcolepsy is the overnight polysomnogram (nPSG) and the multiple sleep latency test (MSLT).  The nPSG is an overnight test that takes continuous, multiple measurements during sleep to detect abnormalities in the sleep cycle.  The PSG can determine whether REM sleep occurs at abnormal times in the sleep cycle, and can rule out the possibility that an individual's symptoms result from another condition.

The MSLT is performed during the day, measuring a person's tendency to fall asleep and to determine whether REM sleep intrudes at inappropriate times.  The sleep latency test measures the amount of time it takes for a person to fall asleep (this is the sleep latency).  The test involves four or five short naps scheduled two hours apart.  Sleep onset eight minutes or earlier into the nap opportunity suggests a disorder of excessive daytime sleepiness, but is not specific for narcolepsy.  The MSLT also indicates the occurrence of abnormally timed REM episodes.  If a person enters REM sleep either at the beginning or within a few minutes of sleep onset during at least two of the scheduled naps, this is considered an indication of narcolepsy.  Other reasons for REM sleep on the MSLT must be ruled out, such as the effects of medication and sleep deprivation from sleep apnea or an irregular work schedule.

Body fluid tests can be helpful in certain cases of suspected narcolepsy.  Low levels of hypocretin in the cerebrospinal fluid is suggestive, as is a genetic marker test performed on blood and looking for specific type of HLA (human leukocyte antigen DQB1*06:02) indicative of the status of the genetic make-up of chromosome 6.  

Treatment for narcolepsy consists of alerting agent that strengthen and consolidate the waking state, such as Provigil (modafinil) or Nuvigil (armodafinil).  Certain antidepressants can help control cataplexy; although the specific treatment Xyrem (sodium oxybate) for both cataplexy and the excessive daytime sleepiness of narcolepsy is effective and available.  Carefully timed and regularly scheduled short naps can be helpful to maintain wakefulness during the times otherwise.  Finally, support groups also provide individuals with a network of social contacts who can offer practical help and emotional support.

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