Narcolepsy/Cataplexy is a disorder of sleep in which the mechanisms which control sleep and arousal are abnormal. The cause is unknown. The components of narcolepsy include excessive daytime drowsiness, cataplexy, hypnogogic hallucinations and sleep paralysis. New medications have introduced recently which have significantly improved the treatment of narcolepsy.
REM SLEEP
To understand Narcolepsy, one must know something about the qualities of rapid-eye movement sleep (REM sleep). REM is a basic component of normal sleep which occurs in discreet episodes throughout the night, occupying approximaterly 20% of a young adult's normal sleep, and is associated with the vivid dreams which contain a plot. The first episode of REM occurs with remarkable regularity approximately 90 minutes after a normal adult goes to sleep for the night. If this REM latency is significcantly shorter or longer, a cause should be determined. The EEG pattern of REM appears more like that of an awake individual; thus, the older term of "paradoxic sleep". During REM, striking and rapid movements of the eyes can be seen and recorded in the sleep study, giving the name to this stage of sleep. The voluntary or skeletal muscles become temporarily atonic or temporarily paralyzed during REM sleep. Only the eye movements and respiratory movements of the diagphragm continue during REM sleep. One concept of narcolepsy is to consider these elements of REM sleep as appearing inappropriately in wakefulness or early sleep.
The excessive daytime sleepiness of narcolepsy produces an irresistable urge to sleep, despite having had an apparently adequate amount of sleep during the previous night. Naps, which are generaaly only for a few minutes, are refreshing and allow the narcoleptic to function for a short time. However, several naps or short involuntary sleep episodes may intrude during the day.
If a daytime nap study such as the multiple sleep latency study (MSLT) is done, the average time to fall asleep in the narcoleptic subjects is less than five minutes. Usually there are two or more REM episodes during the naps study. Since the naps are limited to 20 minutes, the REM latency is very shortened.
Cataplexy, which represents the atonia of REM sleep, is a sudden loss of muscle tone and strength which may be localized to a region of the body such as the legs or the head and neck or can be generalized and affect the whole body. The weakness is generally the result of asudden startle or surprise. Most often cataplexy is preceded by laughter. In a narcoleptic, a joke can not only cause laughter, but may result in severe weakness or a temporary collapse. Even though the events are brief, in some situations such as driving or climbing a ladder, the cataplexy can be very dangerous.
Sleep paralysis which occurs at the onset of sleep is also suggestive of narcolepsy. Sleep paralysis on awakening may not be as significant. The sleep paralysis suggests the appearance of REM-related muscle atonia, which like cataplexy, occurs at an inappropriate time.
Hypnogogic hallucinations are dream-like sequences occurring at the onset of sleep.
The causes of narcolepsy are not well understood yet. However, recently a novel neurotransmitter system, the hypocretin/orexin system, with neuronal cell bodies in the lateral hypothalamus of the brain have been discovered. These cells project widely to areas of the brain and to areas in the brainstem which control arousal. In certain animal models of narcolpsy/cataplexy and in human patients with narcoplexy/cataplexy, the hypocretin/orexin levels are very low or absent. There may lso be genetic, environmental or auto-immune factors as well.
DIAGNOSIS
The diagnosis of narcolepsy in a patient with symptoms suggestive of narcolepsy should include a history and physical examination and a sleep study. A full night polysomnogram(PSG) is done to rule other conditions which can mimic the extreme sleepiness of narcolepsy. If no explanation for the daytime symptoms are seen on the sleep study, an MSLT is done, beginning the morning following the sleep study. in the MSLT, the patient is given four or five nap opportunities, each lasting 20 minutes at two hour intervals. If the mean sleep latency (the time it takes to fall asleep) is less than five minutesand if REM sleep appears in two or more of the naps, the diagnosis of narcolepsy is confirmend.
TREATMENT
The current treatment is to use a stimulant, most often modafinil, to maintain alertness; and another medication to prevent the cataplexy. In the past, tricyclic anti-depressants were very helpful in treating the cataplexy, but they had significant side effects such as drowsiness. Newer antideprressants, the selective serotonin re-uptake inhibitors (SSRI's) have also been used. A new medication, sodium oxybate, has been released for the treatment of cataplexy. Sodium oxybate is the first drug to have a specific FDA approval for the treatment of cataplexy. The mode of action in treating the cataplexy is not well known, but it has been the most effective treatment for the cataplexy yet. Because of its beneficial effects on nocturnal sleep, it may also help the severe daytime sleepiness as well. Behavioral treatments such as scheduled naps may also be very helpful in controlling the excessive sleepiness.