Circadian rhythm sleep disorder

Definition

Circadian rhythm sleep disorder is a persistent or recurring pattern of sleep disruption resulting either from an altered sleep-wake schedule or an inequality between a person's natural sleep-wake cycle and the sleep-related demands placed on him or her. The term circadian rhythm refers to a person's internal sleep and wake-related rhythms that occur throughout a 24-hour period. The sleep disruption leads to insomnia or excessive sleepiness during the day, resulting in impaired functioning.

The Fourth Edition Text Revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IVTR, a handbook used by mental health professionals to diagnose mental disorders) defines circadian rhythm sleep disorder as one of several primary sleep disorders . Within the category of primary sleep disorders, it is classified as one of the dyssomnias, characterized by irregularities in an individual's quality, timing, and amount of sleep. In earlier versions of the DSM, the disorder is called sleep-wake schedule disorder.

Description

Circadian rhythm sleep disorder involves an alteration of an individual's circadian system or a mismatch between a person's natural, or endogenous, circadian system and the external, or exogenous, demands placed on it. It can lead to insomnia at certain times of the day or excessive sleepiness throughout the day. The insomnia or excessive sleepiness results in impaired functioning in social, occupational, or other environments.

The DSM-IV-TR lists four types of circadian rhythm sleep disorder: delayed sleep phase type, jet lag type, shift work type, and unspecified type.

Causes and symptoms

Causes

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.

The jet lag type of circadian rhythm sleep disorder is characterized by disruptions arising from a mismatch between a person's circadian cycle and the cycle required by a different time zone. The more time zones that are traveled, the greater the disruption. Eastbound travel, in which sleep-wake hours are advanced, typically causes more problems than westbound travel, in which sleep-wake hours are delayed. People who travel often and cross many time zones when they travel are most susceptible to this type.

The shift work type of circadian rhythm sleep disorder is distinguished by disruptions due to a conflict between a person's endogenous circadian cycle and the cycle required by shift work. Individuals who work the night shift often experience this problem, especially those people who switch to a normal sleep schedule on days off. Also, people who work rotating shifts experience this problem because of the changing sleep-wake schedules they experience. The disruptions caused by shift work result in inconsistent circadian schedules and an inability to adjust to the changes consistently.

The unspecified type of circadian rhythm sleep disorder is characterized by a pattern of sleep-wake disturbance and circadian mismatch that is not due to the causes of the other three types. Examples of other causes include irregular sleep-wake patterns and non-24-hour sleep-wake patterns. If an individual's sleep-wake pattern is based on a period of time of slightly more than 24 hours, their circadian rhythm can become progressively delayed.

Symptoms

Individuals with the delayed sleep phase type of the disorder exhibit habitually late sleep hours and an inability to change their sleeping schedule consistently. They often show sleepiness during the desired wake period of their days. Their actual phase of sleep is normal. Once they fall asleep, they stay asleep for a normal period of time, albeit a period of time that starts and stops at an abnormally late time.

Individuals with the jet lag type of circadian rhythm sleep disorder demonstrate sleepiness during the desired wake portion of the day due to the change in time zone. They have difficulty sleeping during the desired sleep portion of the day. They also have difficulty altering their sleep-wake schedule to one appropriate to the new time zone.

Individuals with the shift work type of the disorder feel sleepy or fall asleep during the desired wake period, which includes the time spent at work. People with rotating shift schedules, especially schedules that gradually change, exhibit sleep disturbance and wake period sleepiness. Insufficient sleep time, family and social expectations, and alcohol use worsen this problem.

Individuals with the unspecified type of circadian rhythm sleep disorder also exhibit daytime and evening sleepiness or insomnia, especially those people who have a non-24-hour sleep pattern. People with irregular sleep patterns have difficulty knowing when they will fall asleep and wake up.

Demographics

The delayed sleep phase type of the disorder usually begins during adolescence and can continue without treatment through adulthood. People with this type may have a family history of delayed sleep phase. The delayed sleep phase type of the disorder is thought to impact up to 4% of adults and up to 7% of adolescents.

The shift work and jet lag types of the disorder often result in more severe symptoms for late-middle-aged and elderly people. It is estimated that up to 60% of night shift workers have the shift work type of circadian rhythm sleep disorder.

Diagnosis

In order to diagnose circadian rhythm sleep disorder, patients are often asked for records of their sleep and wake times in order to determine if a diagnosis is warranted. Interviews and direct observation in a sleep lab may also be utilized. A diagnosis requires a pattern of sleep disruption caused by a mismatch between a person's circadian sleep-wake pattern and the pattern required by that person's environment. The disruption can be persistent or recurrent and leads to impaired functioning, often in a social or occupational context.

To differentiate circadian rhythm sleep disorder from other diagnoses, the sleep disruption must not occur exclusively during the cause of another sleep disorder or other disorder. The disturbance in sleep must not be due to the direct physiological effects of a substance, whether used for medication or abuse, or to a general medical condition.

The delayed sleep phase type of the disorder requires a persistent pattern of delayed sleeping and awakening and an inability to change the pattern. The jet lag type requires sleepiness and wakefulness at inappropriate times relative to the local time zone; there must be repeated travel more than one time zone away. The shift work type requires excessive sleepiness during the desired wake period and an inability to sleep during the desired sleep period, both due to changing shift work or night shift work.

Diagnosis of any type of circadian rhythm sleep disorder must be distinguished from normal adjustments a person makes in reaction to a schedule change. The sleep disruptions must be persistent and recurring and lead to social or occupational problems. People who prefer unusually late or early sleep schedules or people adjusting to a new sleep schedule should not receive this diagnosis unless they meet the other criteria.

Treatments

Treatment of the delayed sleep phase type depends on the severity of the case. Mild cases may be addressed by an individual simply adhering to strict sleep and wake times. Severe cases may require incremental changes in sleep time, where a person sleeps 15 to 30 minutes earlier each day until an appropriate pattern is reached. Other methods of altering delayed sleep patterns include prescribing a night of sleep deprivation or the use of chronotherapy, a method in which sleep is delayed for three hours each night until the sleep pattern is rotated around the clock.

Often, treatment is ignored for persons with the jet lag type because people eventually return to their regular time zone and normal sleep-wake cycle and no longer exhibit symptoms. For people who travel often, it is preferable to adjust to the new time zone by sleeping at times appropriate to that zone if they intend to be there for one week or longer. Diets that target jet lag are also effective for some people, and light therapy , which involves exposure to a lighted device to simulate daytime, may be helpful to some people to adjust to new time zones.

People with the shift work type of the disorder benefit most from a non-changing work schedule. If rotating or changing shifts are unavoidable, rotations that occur in a clockwise direction, where shifts get progressively later and later, are preferable to those in a counter-clockwise direction. Also, when attempting to sleep, it is a good idea to create a comfortable sleeping environment by eliminating daytime noise and light.

Prognosis

Individuals with delayed sleep phase type often have great difficulty changing their sleep patterns and when they are able to change their circadian cycle, they have difficulty maintaining the changes.

People with jet lag type or shift work type can reduce symptoms often by simply decreasing the amount of travel or returning to a normal work schedule. When these changes are not possible, these individuals have trouble making the constant adjustments required to sleep and wake. People with the shift work type often report a reversal of symptoms two weeks after returning to a normal work and sleep schedule.

Prevention

Because circadian rhythm sleep disorder is usually related to environmental stressors, avoidance of these stressors (such as long-distance travel, shift work, and sleep-disrupting lifestyles) can prevent the disorder from beginning or continuing. People who are able to adhere strictly to a normal sleep-wake schedule can also offset circadian rhythm-related problems.

See also Breathing-related sleep disorder; Sleep disorders

Resources

BOOKS

American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th edition, text revised. Washington, DC: American Psychiatric Association, 2000.

Buysse, Daniel J., Charles M. Morin, and Charles F. Reynolds III. "Sleep Disorders." In Treatments of Psychiatric Disorders, edited by Glen O. Gabbard. 2nd edition. Washington, DC: American Psychiatric Press, 1995.

Hobson, J. Allan, and Rosalia Silvestri. "Sleep and Its Disorders." In The Harvard Guide to Psychiatry, edited by Armand M. Nicholi, Jr., M.D. Cambridge, MA: Belknap Press of Harvard University Press, 1999.

Thorpy, Michael J., M.D., and Jan Yager, Ph.D. The Encyclopedia of Sleep and Sleep Disorders. 2nd edition. New York: Facts on File, 2001.

ORGANIZATIONS

American Sleep Disorders Association. 6301 Bandel Road NW, Suite 101, Rochester, MN 55901. <http://www.asda.org>.

Ali Fahmy, Ph.D.

Circadian Rhythm

The circadian rhythm describes the internal biological clock that controls an organism's daily activity cycles. It is well-known that in many species, activity does in fact follow daily patterns. This applies to activities such as feeding or sleeping, as well as to physiological attributes such as metabolic rate, body temperature, blood pressure, and hormone levels. Most animal and plant species have daily rhythms and even fairly simple creatures like bacteria have been known to have natural daily cycles.

Experiments in which organisms are placed in constantly light or constantly dark environments frequently indicate that daily periodicity in activity patterns persists even when the normal day-night cues from sunlight are removed. These circadian rhythms are important in allowing for the timing of important daily activities.

Circadian Cycles

Circadian rhythms typically describe a twenty-four-hour cycle that corresponds to the length of the day on Earth. However, for almost all species, the "natural" cycle is either a little shorter or a little longer than twenty-four hours. This explains the origin of the term "circadian" rhythm: circa means "about" and diem refers to "day." Thus, circadian means "about a day."

Changing light cues from the external environment allow organisms to adjust their natural body clocks and conform to a twenty-four-hour day. Research on circadian rhythms in humans has shown that the human body naturally drifts toward a twenty-five-hour cycle in constant-light conditions.

The ways in which circadian rhythms are controlled vary among biological organisms. In many vertebrate species, circadian rhythms are controlled by the hormone melatonin. Melatonin production follows a daily cycle, high during the night hours and low during daylight hours. (Because increased levels of melatonin production cause sleepiness, it is sometimes used as a sleeping aid.) Melatonin is produced by endocrine cells in the pineal gland, which is located in the central part of the brain. Ultimately, melatonin cycling responds to light cues from the environment.

In some species, such as certain fishes and lizards, a minute hole in the otherwise bony skull allows light to pass directly to the pineal gland. In this way, the pineal gland receives direct information from the external environment on day-night cycles. However, direct exposure of light to the pineal gland is not necessary. In birds, photoreceptors in the eyes as well as in the brain are responsible for transmitting signals to the part of the brain that controls circadian rhythms.

In mammals, the eyes alone appear to be responsible for photoreception related to circadian cycles. This involves a special pigment (a light-absorbing molecule) called crytochrome that is present in mammalian eyes. Crytochrome is distinct from the pigments that are responsible for vision, and is also found in a different part of the retina. In certain cases of blindness, the circadian rhythm is not disrupted because the parts of the retina that contain crytochrome are intact.

Problems Linked to Circadian Rhythm

Circadian rhythms impact everyday human life in many ways.

Jet lag.

Jet lag, which can be the result of travel across several time zones, is caused by discrepancies between an individual's internal clock and signals provided by the external environment. The body generally adjusts to jet lag over the course of a few days as it is exposed to daylight patterns in the new time zone. Working the night shift can also be problematic for humans, because humans are naturally diurnal , that is, active during the day and asleep at night. Data indicate that the majority of industrial accidents occur at night, when the body is programmed to slow down in preparation for sleep.

Seasonal affective disorder (SAD).

Seasonal affective disorder (SAD), which can result in extreme depression during the winter months, may also be related to the operation of circadian clocks. SAD strikes when the days are short and light is scarce. SAD is particularly common at high latitudes, where the days are particularly short during the winter. Short light cycles are likely to disrupt the circadian clock, although the link to depression has not been demonstrated. Regular exposure to artificial bright lights is often effective in treating SAD.

Sleep disorders.

Certain sleep disorders, not surprisingly, are related to problems with circadian rhythms. Older people, for example, produce less melatonin. This may be linked to the sleeping patterns associated with age, such as insomnia, early rising, and sleepiness during the day. Delayed sleep phase syndrome (DSPS), which has also been linked to old age, is a more serious problem that causes people to want to sleep from early morning to noon, instead of during more typical night hours.

Circadian rhythms are only one example of the broader category of biological rhythms. Biological rhythms range widely in duration, with circadian rhythms being among the shortest. Other biological activities follow longer cycles, such as lunar cycles, or even periods of several months or a year. The menstrual cycle and seasonal mating activity are examples of processes that occur cyclicly, but over a longer time period.

see also Diurnal; Nocturnal.

Jennifer Yeh

Bibliography

Gould, James L., and William T. Keeton. Biological Science, 6th ed. New York: W. W. Norton, 1996.

Withers, Philip C. Comparative Animal Physiology. Fort Worth, TX: Saunders College Publishing, 1992.

circadian rhythm The approximately 24-hourly pattern of various metabolic activities seen in most organisms. The rhythmic patterns may persist even when the organism is removed from exposure to 24-hour cycles of light and dark. In a natural habitat the rhythm is 24-hourly; in constant conditions it becomes slightly longer or shorter than 24 hours. The rhythm is controlled by an endogenous biological clock that is reset by cues (e.g. dawn) from the environment. The word is derived from the Latin circa, ‘about’, and dies, ‘day’. The different types of activity rhythm are classified as cathemeral, crepuscular, diurnal, and nocturnal.

circadian rhythm The approximately 24-hourly pattern of various metabolic activities seen in most organisms. The rhythmic patterns may persist even when the organism is removed from exposure to 24-hour cycles of light and dark. In a natural habitat the rhythm is 24-hourly; in constant conditions it becomes slightly longer or shorter than 24 hours. The rhythm is thought to be controlled by an endogenous biological clock, though little is known about the sites and modes of action of the mechanisms involved. The word is derived from the Latin circa, meaning ‘about’ and dies, meaning ‘day’.

circadian rhythm The approximately 24-hourly pattern of various metabolic activities seen in most organisms. The rhythmic patterns may persist even when the organism is removed from exposure to 24-hour cycles of light and dark. In a natural habitat the rhythm is 24-hourly; in constant conditions it becomes slightly longer or shorter than 24 hours. The rhythm is thought to be controlled by an endogenous biological clock, though little is known about the sites and modes of action of the mechanisms involved. The word is derived from the Latin circa, meaning ‘about’ and dies, meaning ‘day’.

circadian rhythm Internal ‘clock’ mechanism found in most organisms. It normally corresponds with the 24-hour day, relating most obviously to waking and sleeping cycles, but is also involved in other cyclic variations, such as body temperature, hormone levels, metabolism and mental performance.

circadian rhythm (diurnal rhythm) Any 24-hour periodicity in the behaviour or physiology of animals or plants. Examples are the sleep/activity cycle in many animals and the growth movements of plants. Circadian rhythms are generally controlled by biological clocks.

circadian rhythm (ser-kay-diăn) n. the periodic rhythm, synchronized approximately to the 24-hour day/night cycle, seen in various metabolic activities of most living organisms (e.g. sleeping, hormone secretion).

circadian rhythm see rhythm, biological .