|Circadian rhythm sleep disorder|
|Classification and external resources|
Circadian rhythm sleep disorders are a family of sleep disorders affecting, among other things, the timing of sleep. People with circadian rhythm sleep disorders are unable to sleep and wake at the times required for normal work, school, and social needs. They are generally able to get enough sleep if allowed to sleep and wake at the times dictated by their body clocks. Unless they have another sleep disorder, their sleep is of normal quality.
Humans, like most animals and plants, have biological rhythms, known as circadian rhythms, which are controlled by a biological clock and work on a daily time scale. These affect body temperature, alertness, appetite, hormone secretion etc. as well as sleep timing. Due to the circadian clock, sleepiness does not continuously increase as time passes. A person's desire and ability to fall asleep is influenced by both the length of time since the person woke from an adequate sleep, and by internal circadian rhythms. Thus, the body is ready for sleep and for wakefulness at different times of the day.
The circadian rhythm sleep disorders are:
Among people with healthy circadian clocks, there is a continuum of chronotypes from "larks", "morning people", who prefer to sleep and wake early, to "owls", "evening people" or "night people", who prefer to sleep and wake at late times. Whether they are larks or owls, people with normal circadian systems:
Researchers have placed volunteers in caves or special apartments for several weeks without clocks or other time cues. Without time cues, the volunteers tended to go to bed an hour later and to get up about an hour later each day. These experiments appeared to demonstrate that the "free-running" circadian rhythm in humans was about 25 hours long. However, these volunteers were allowed to control artificial lighting and the light in the evening caused a phase delay. More recent research shows that adults of all ages free-run at an average of 24 hours and 11 minutes. To maintain a 24-hour day/night cycle, the biological clock needs regular environmental time cues or Zeitgebers, e.g., sunrise, sunset, and daily routine. Time cues keep the normal human circadian clock aligned with the rest of the world.
Non-24-hour sleep-wake syndrome and other persistent circadian rhythm sleep disorders are believed to be caused by an inadequate ability to reset the sleep/wake cycle in response to environmental time cues. These individuals' circadian clocks might have an unusually long cycle, and/or might not be sensitive enough to time cues. People with DSPS, more common than Non-24, do entrain to nature's 24 hours, but are unable to sleep and awaken at socially preferred times, sleeping instead, for example, from 4 a.m. to noon. According to doctors Cataletto and Hertz at WebMD, "Altered or disrupted sensitivity to zeitgebers is probably the most common cause of circadian rhythm disorder."
As of October 1, 2005, the diagnostic codes for circadian rhythm sleep disorders were changed from the 307-group to the 327-group in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR). The DSM updated to agree with the International Classification of Diseases (ICD-9). The new codes reflect the moving of these disorders from the Mental Disorders section to the Neurological section in the ICD.
Possible treatments for circadian rhythm sleep disorders include: Behavior therapy where the patient is told to avoid naps, caffeine and other stimulants. They are also told to not be in bed for anything besides sleep and sex. Bright Light Therapy is used to advance or delay sleep depending on how the circadian rhythm is shifted. Patients are exposed to high intensity light (10,000 lux) for a duration of 30-60 minutes at a time, several times a day. Medications such as melatonin, a naturally occurring sleep aid, or other wake promoting agents or short term sleep aids can be beneficial. Chronotherapy progressively advances or delays the sleep time by 1-2 hours per day 
| The English used in this article or section may not be easy for everybody to understand.
You can help Wikipedia by making this page or section simpler.
Cause The delayed sleep phase type of circadian rhythm sleep disorder is marked by a delay of the sleep-wake cycle as it relates to the demands of society. It is often due to a psychosocial stressor (an event in a person's environment that causes stress or discomfort), especially for adolescents. The delayed sleep-wake cycle leads to chronic sleep deprivation and habitually late sleeping hours. Individuals with this type often have difficulty changing their sleeping patterns to an earlier and more socially acceptable time. Their actual sleep, once it begins, is normal. It is the timing of their sleeping and waking that is persistently delayed.
Jet Lag often affects people who have travelled several hours east or west, through several time zones. It may take many days for the body to adjust to the new environment. The name comes from travelling by jet aircraft.
Intrinsic refers to something which happens or is caused within a system or an organism. There are four circadian rhythm sleep disorders of the intrinsic type. Unless they are caused by a head injury or by a disease, they are usually genetic, that is, people are born with them. They are generally chronic; they do not go away, but they may to some degree be treated.
Advanced sleep-phase syndrome (ASPS) is very rare. People with this syndrome are sleepy very early in the evening and they sleep from about 19:00-20:00 in the evening to about 03:00-04:00 in the early morning. Their sleep is usually normal. There are often several people in the same family who have ASPS.
Delayed sleep-phase syndrome (DSPS) is the opposite of ASPS, and it is more common, affecting about 0.15% of adults. It usually starts in early childhood or at puberty. Some cases which start at puberty go away when the person is about 20 years old. Otherwise, the syndrome does not go away, that is, it is chronic.
People with DSPS cannot go to sleep before 03:00-06:00 in the morning, or even later. They sleep normally for 8-9 hours, but they cannot wake up in time for school or a job which starts in the morning. They can go to sleep at the same time every night and get up at the same time each day. This means that they are entrained (adjusted, synchronized) to the daily light/dark cycle. Even when they try to sleep at acceptable times, they are most alert in the late evening and the nighttime hours.
Non-24-hour sleep-wake syndrome (Non-24) is quite rare. Some people who can see have it, but it is more common among the blind. People with Non-24 sleep well for 8-9 hours, but they do not adjust to the daily light/dark cycle at all. Therefore, they go to sleep 1-2 hours later each day and wake up 1-2 hours later than the day before. This is called freerunning sleep. Their times of best alertness, appetite, body temperature rhythm and hormone cycles all move continuously around the clock, coming back to the same time after a few weeks.
Irregular sleep-wake disorder is quite rare, and it is often possible to find out what causes it, for example, a head injury, a mental handicap, dementia or some other sicknesses. People with this disorder sleep and wake several times a day, but not at the same times every day. Altogether they sleep the same number of hours as other people of the same age.
Treatment for these disorders is similar, and it often does not work very well. In addition, it can be difficult to find a doctor who knows much about circadian rhythms, as the field of study is quite new.
Treatment with bright light is also called phototherapy or light therapy. People with ASPS need a lot of light in the evening and they should avoid bright light in the morning. People with DSPS need bright light as soon as they wake up and should try to avoid bright light in the evening.
Melatonin is a hormone produced in the pineal gland in the brain. It is normally only produced in the evening and at night. People with ASPS can take melatonin by mouth in the morning. People with DSPS can take melatonin in the afternoon or evening, and this treatment works also for some people with Non-24.
Similar treatments can be tried for the other disorders.