Narcoleptics are very sleepy except during the minutes after they awaken from sleep. Their nighttime sleep is fragmented by repeated awakenings. In cataplexy emotional excitement triggers the abrupt onset of twitching of small face muscles, inarticulate speech, drooping of upper eyelids, limpness of the neck, sagging in a chair or sinking to the floor with preserved consciousness. Laughter, surprise, and anger are common precipitants. Muscle weakness typically occurs for seconds or minutes. The narcoleptic is likely to fall asleep if this weakness persists for more than two minutes. Sleep paralysis is the temporary inability to talk or move while falling asleep or awakening. It is commonly accompanied by dream-like images or, less frequently, accompanied by hallucinations of touch, voices, or the sense that there is an intruder in the sleep environment. These are called hypnogogic when they occur as one is going to sleep or hynopompic when awakening. The symptoms of narcolepsy, except for cataplexy, which occurs only very rarely in non-narcoleptics, also occur in people who do not have narcolepsy. They tend to persist throughout life from the time of onset. Most often excessive sleepiness begins months or years before the onset of cataplexy.
200,000 Americans have narcolepsy, however, only a quarter are diagnosed. Often there is an interval of many years between the onset of symptoms and the establishment of the correct diagnosis. During this time, incorrect diagnoses are often made and inappropriate treatments initiated.
Narcolepsy occurs in a roughly equal number of males and females and may begin at any age. However, the most common age of onset is the teens or twenties.
Unlike non-narcoleptics who typically develop dreaming or rapid eye movement (REM) sleep an hour or more after they fall asleep, narcoleptics tend to enter REM sleep within minutes of sleep onset. REM sleep is characterized by paralysis of voluntary muscles except for the small muscles that move the hands, toes, and eyes. Dreams are more likely to occur during REM compared with non-REM sleep. The sleep paralysis and cataplexy of narcoleptics along with the hallucinations, closely resemble the normal events of REM sleep.
The diagnosis of narcolepsy is highly likely when severe sleepiness is associated with cataplexy. The presence of other cardinal symptoms and positive results of sleep testing support the diagnosis, especially when cataplexy is absent. Diagnostic testing typically includes an overnight polysomnogram (PSG) to investigate other possible causes of excessive sleepiness (e.g., sleep apnea or periodic limb movements during sleep) and to make sure that the patient is not lacking REM sleep. Following the overnight, the patient completes a mean sleep latency test (MSLT) during which the patient is given four to five nap opportunities to sleep. The patient is not allowed to sleep for more than 15 minutes during each nap opportunity. Narcoleptics usually have the onset of Stage REM during two or more of the MSLT naps. Importantly, if there is a lack of Stage REM during the night immediately prior to an MSLT, sleep onset REM activity may represent a normal rebound of Stage REM rather than narcolepsy. Even with a normal amount of Stage REM the night before, as documented by the PSG , narcoleptics tend to have two or more sleep onset REM periods during an MSLT.
Only one to two percent of narcoleptics with cataplexy have immediate family members with narcolepsy. Eight to twelve percent of people with excessive sleepiness and other associated symptoms of narcolepsy without cataplexy have a higher incidence of hypersomnolence and associated symptoms in their immediate family. Although the genetics of human narcolepsy, as opposed to dog narcolepsy, appear to be complex, 90% or more of narcoleptics with cataplexy, and a smaller majority of those without cataplexy, have a narcolepsy susceptibility gene. When one identical twin has narcolepsy with cataplexy, the other twin has a one of three chance of having narcolepsy. Therefore, genes do not alone determine whether an individual will develop narcolepsy.
There is no cure for narcolepsy however, the symptoms can be partially relieved. Sleepiness can be reduced by stimulants or by twice nightly doses of oxybate, a natural substance that consolidates sleep. A variety of antidepressant medications can reduce cataplexy however, oxybate is more potent. A regular sleep wake schedule and taking periodic naps during the day and evening can also be helpful.