What is Sleep Medicine?
Narcolepsy
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 approximately 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 significantly 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 diaphragm 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 irresistible urge to sleep, despite having had an apparently adequate amount of sleep during the previous night. Naps, which are generally 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 a sudden 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 hypocretinorexin 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 hypocretinorexin levels are very low or absent. There may also 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 minutes and if REM sleep appears in two or more of the naps, the diagnosis of narcolepsy is confirmed.
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 antidepressants, 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.
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Sleep Apnea
Sleep apnea is a very common disorder (up to 10% of men and up to 5% of women) of sleep in which breathing stops while a person is asleep. There are two types of sleep apnea, obstructive and central.
In obstructive sleep apnea, the upper airway becomes obstructed or blocked by the collapse of the soft palate, the tongue and the airway above the voice box (larynx). In people who are predisposed, these tissues sag into the airway as the muscles relax during sleep. As a result, the flow of air is impeded (hypopnea) or stops completely (apnea). As the brain continues to drive breathing movements, the airway collapse becomes worse. Similar in concept is the collapse of a paper soda-straw when one sucks too hard in drinking a thick drink.
Eventually, the brain is forced to arouse itself in order to restart breathing. During the apneas and hypopneas, the blood oxygen level, measured by the oxygen saturation, falls. There may be other events such as irregular heart rhythms or limb movements as well. Because the obstruction/apneas can be very frequent through the sleep period, sleep becomes fragmented.
Sleep is a very orderly process, normally progressing through early, more superficial stages to the deeper more restful, restorative stages. With each arousal the process must start all over again, which interrupts the flow of sleep and may deprive the patient of the more restorative stages and continuity of sleep.
Symptoms of sleep apnea can be predicted with this process in mind. Snoring is the most common problem and is usually reported by spouses, bedmates, roommates, family and sometimes neighbors. Patients awaken in the morning feeling un-refreshed, as though they have not slept well or at all. Spouses may observe pauses in the breathing which represent apneas. Patients usually have some degree of of increased or excessive daytime sleepiness especially when inactive (ex. reading, doing paperwork or driving). Patients often have get up from sleep at night to urinate and may note that they have been sweating in their sleep. There may also be morning headaches. Inability to concentrate and memory disturbance is common.
Much less frequently, the brain may simply not stimulate an effort to breathe. This is central apnea. Occasionally, this may be from unknown causes or may be the result of neurologic disorders such as stroke or other neuromuscular disorders.
The excessive daytime sleepiness causes a loss of life quality, and the apneas and snoring may cause marital distress due to the impact on the spouse's sleep. There is mounting evidence that sleep apnea is also associated with heart attack, stroke hypertension and trauma (from falling asleep at the wheel or in some other inappropriate situation in which to sleep), resulting in an increased mortality rate.
The diagnosis of sleep apnea is confirmed by doing a sleep study (polysomnogram) which demonstrates the apneas and/or hypoppneas.Generally, a second sleep study is done in which CPAP (continuous positive airway pressure) is introduced. CPAP opens the airway much as one blows air into a balloon to inflate the dome of the balloon. Air pressure and airflow is generated by an air pump which is connected to a mask via flexible tubing. The mask fits over the nose (multiple mask types are available for the nose, mouth or the whole face) and is held in place by soft straps around the head.
CPAP is currently the most effective form of treatment. Usually, there is significant improvement in the patient's symptoms. The snoring relieved and the apneas stop. As a result, the person's sleep improves and the daytime sleepiness and fatique clear. The risk of stroke, heart attack and trauma drop to level that would be experienced without the sleep apnea. Other treatment options include surgery to remove excessive tissue from the airway or open the nasal passages. Also, a device can be fitted to pull the lower jaw forward to increase the front-to-back diameter of the airway.
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What is Sleep Medicine?
Literally, sleep medicine deals with the clinical problems of disturbed sleep. Since the first truly clinical sleep disorders centers and laboratories were developed in the late ‘60’s’ and early 70’s, over three hundred sleep disorder diagnoses have been identified and codified. This incredible explosion of information and direct application to the diagnosis and treatment of patients has lead to the establishment of this specialty of medicine. At the same time a parallel development in technology has allowed us to more easily and accurately study the processes of sleep and apply it to the problems that patients present.
Recognition of these problems is now accepted as an important part of the overall treatment and health of patients. Not only do sleep disorders affect other medical problems, but they have a strong impact on the cost of medical care. As an example, Undiagnosed or untreated sleep apnea my double the money spent on healthcare. New information shows that some undiagnosed or untreated sleep disorders may have a life or death impact.
In any give sleep laboratory, the most common diagnosis that leads to a sleep study is sleep apnea. Sleep apnea results in the obstruction of the upper airway when the patient falls asleep. Breathing can resume only on arousal from sleep. As a result of frequent arousals over the night’s sleep, normal sleep is fragmented and inefficient. The appropriate amounts of essential stages of sleep cannot be achieved and sleep deprivation occurs.
There are many other dramatic and colorful, even bizarre problems that occur with sleep. Fortunately, most if not all can be diagnosed and usually treated successfully. While there are a few sleep disorders that are definitely life threatening, most of these disorders affect the quality of one’s life. Certainly, a good night’s sleep helps us all to feel and function at our peak.
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