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Narcolepsy

Description

An in-depth report on the causes, diagnosis, and treatment of narcolepsy.

Introduction

The word narcolepsy comes from two Greek words roughly translated as "seized by numbness". The two primary symptoms in narcolepsy reflect this phrase:

• Excessive daytime sleepiness, with frequent daily sleep attacks or a need to take several naps during the day.
• Temporary and sudden muscle weakness (called cataplexy ), usually brought on by strong emotions.

Some, but not all patients experience other symptoms:

• Microsleep episodes, in which the patient behaves automatically but without conscious awareness.
• A sense of paralysis that occurs between wakefulness and sleep (called atonia ).
• Dream-like states between waking and sleeping (called hypnagogic hallucinations ).
• Periodic leg movements during sleep ( periodic limb movement disorder ).

REM (rapid eye movement) sleep is abnormal in narcolepsy. In fact, narcolepsy is sometimes defined as the loss of boundaries between wakefulness, non-REM sleep, and REM sleep. REM sleep is the active, dreaming phase of sleep.

Primary Symptoms of Narcolepsy

Excessive Sleepiness. All people with narcolepsy experience excessive sleepiness during the day with episodes of falling asleep rapidly and inappropriately, even when fully involved in an activity. These events may be characterized by the following behaviors:

• Periods of drowsiness may occur every 3 or 4 hours and usually end in short naps.
• Patients may sleep for a few minutes, particularly if they are in an awkward position or for a few hours if they are lying down.
• Patients often underestimate the duration of their drowsy periods and may not recall clearly their behavior during that time.

Cataplexy. Cataplexy is an abrupt loss of muscle tone or strength that results in an inability to move and always occurs during wakefulness. It occurs in about two-thirds of narcolepsy patients and may be triggered by the following events:

• Sudden emotion, usually anger or laughter (the most common trigger)
• Following a heavy meal
• During periods of stress

Muscle reflexes are completely absent during a cataplectic attack. Cataplectic attacks can be very minimal and appear as passing weakness or affecting only the eyelids and face. They may, on the other hand, be so severe that they weaken the whole body. The most severe form is called status cataplectics, which occurs repeatedly for hours or days. Abrupt withdrawal from certain drugs used to treat narcolepsy, notably clomipramine, can cause status cataplectics.

Cataplexy may have the following characteristics:

• Most attacks last less than 30 seconds and can be missed by even skilled observers. However, on severe cases, a person may fall and remain paralyzed for as long as several minutes.
• Typically the patient's head will suddenly fall forward, the jaw becomes slack, and the knees will buckle.
• Speech may become suddenly loud or broken and stutter-like.

Other Symptoms of Narcolepsy

Atonia. Atonia is a sense of paralysis that occurs between wakefulness and sleep, usually upon waking or sometimes at the onset of sleep. The person is conscious but cannot speak, move (cannot even open the eyes), and cannot breathe deeply. Atonia rarely lasts beyond 20 minutes, but when it first occurs, this experience can be terrifying, particularly if the patient also develops hallucinations.

Hypnagogic Hallucinations. Hypnagogic hallucinations are dreams that intrude on wakefulness, which can cause visual, auditory, or touchable sensations. They occur between waking and sleeping, usually at the onset of sleep, and can also occur about 30 seconds after a cataplectic attack.

• Visual hallucinations have been described as a "film running through the head" or as a waking dream with strong emotional content. Images can be intrusive. More commonly they may involve seeing colored forms that shift in size and shape.
• Auditory hallucinations may include random sounds or elaborate melodies.
• A person may also hallucinate feelings of rubbing or light touches, even levitation.

Such symptoms may also appear in other sleep disorders and are probably related to extreme sleepiness. In general, cataplexy must also be present for a clear diagnosis of narcolepsy. Some experts believe, however, that some patients with narcolepsy may experience hypnagogic hallucinations and daytime sleepiness and not cataplexy.

Microsleep and Automatic Behavior. In some cases, patients have so-called microsleep episodes, in which they behave automatically without conscious awareness. Such automatic behavior may not be recognized as part of a disorder by either patients or the people around them. Some examples include:

• People with narcolepsy can be driving or walking competently but end up in a location different from the intended one.
• A narcolepsy patient can be carrying on a conversation and jump from one unrelated topic to another or just trail off and stop talking altogether.
• The patient may suddenly perform bizarre actions, such as putting socks in the refrigerator.
• Patients may experience severe forgetfulness.
• Their movements may suddenly become slow or clumsy.
• In some cases, their behavior may resemble some forms of epileptic seizures.

Disturbed Sleep. Nighttime sleep is often disturbed in narcolepsy, but it is usually mild to moderate and does not account for the daytime sleepiness experienced by people with narcolepsy.

Periodic Limb Movement Disorder. Many patients with narcolepsy experience periodic limb movement disorder, also called PLMD (formerly known as nocturnal myoclonus). In PLMD, the leg muscles involuntarily contract every 20 to 40 seconds during sleep, occasionally arousing the patient. The patient is usually unaware of the cause of the interruption.

Healthy Sleep In sleep studies, subjects spend about one-third of their time asleep, suggesting that most people need about 8 hours of sleep each day. Individual adults differ in the amount of sleep they need to feel well rested, however. (Infants may sleep as many as 16 hours a day.) The daily cycle of life, which includes sleeping and waking, is called a circadian (meaning "about a day") rhythm, commonly referred to as the biologic clock. Hundreds of bodily functions follow biologic clocks, but sleeping and waking comprise the most prominent circadian rhythm. The sleeping and waking cycle is approximately 24 hours. (If confined to windowless apartments, with no clocks or other time cues, sleeping and waking as their bodies dictate, humans typically live on slightly longer than 24-hour cycles.) It usually takes the following daily patterns: Humans are designed for daytime activity and nighttime rest. Additionally, there is a natural peak in sleepiness at mid-day, the traditional siesta time. In addition, daily rhythms intermesh with other factors that may interfere or change individual patterns: The fraction-of-a-second-firing of nerve cells in the brain may be faster or slower in different individuals. The monthly menstrual cycle in women can shift the pattern. Light signals coming through the eyes reset the circadian cycles each day, so changes in season or various exposures to light and dark can unsettle the pattern. The importance of sunlight as a cue for circadian rhythms is dramatized by the problems experienced by people who are totally blind. They commonly suffer trouble sleeping and other rhythm disruptions. The Response in the Brain to Light Signals The response to light signals in the brain is an important key factor in sleep: Light signals travel to a tiny cluster of nerves in the hypothalamus in the center of the brain, the body's master clock, which is called the supra chiasmatic nucleus or SCN.

This nerve cluster takes its name from its location, which is just above (supra) the optic chiasm, which is a major junction for nerves transmitting information about light from the eyes. The approach of dusk each day prompts the SCN to signal the nearby pineal gland (named so because it resembles a pine-cone) to produce the hormone melatonin. Melatonin is thought to act as the body's time-setting hormone. The longer a person is in darkness the longer the duration of melatonin secretion. Secretion can be diminished by staying in bright light. Melatonin also appears to trigger the need to sleep. Sleep Cycles Sleep consists of two distinct states that alternate in cycles and reflect differing levels of brain nerve cell activity: Non-Rapid Eye Movement Sleep (NonREM). NonREM sleep is also termed quiet sleep. NonREM is further subdivided into three stages of progression: Stage 1 (light sleep) Stage 2 (so-called true sleep) Stage 3 to 4 (deep "slow-wave" or delta sleep) With each descending stage, awakening becomes more difficult. It is not known what governs NonREM sleep in the brain. A balance between certain hormones, particularly growth and stress hormones, may be important for deep sleep. Rapid Eye-Movement Sleep (REM). REM sleep is termed active sleep. Most vivid dreams occur in REM sleep. REM-sleep brain activity is comparable to that in waking, but the muscles are virtually paralyzed, possibly preventing people from acting out their dreams. In fact, except for vital organs like lungs and heart, the only muscles not paralyzed during REM are the eye muscles. REM sleep may be critical for learning and for day-to-day mood regulation. When people are sleep-deprived, their brains must work harder than when they are well rested.

The REM/NREM Cycle. The cycle between quiet (NonREM) and active (REM) sleep generally follows this pattern: After about 90 minutes of NonREM sleep, eyes move rapidly behind closed lids, giving rise to REM sleep. As sleep progresses the NonREM/REM cycle repeats. With each cycle, NonREM sleep becomes progressively lighter, and REM sleep becomes progressively longer, lasting from a few minutes early in sleep to perhaps an hour at the end of the sleep episode.

• Review Date: 7/13/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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