Circadian rhythm sleep disorder

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Circadian rhythm sleep disorder
Classification and external resources
ICD-9327.3, 780.55
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Circadian rhythm sleep disorder
Classification and external resources
ICD-9327.3, 780.55

Circadian rhythm sleep disorders (CRSD) 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 also have another sleep disorder, the quality of their sleep is usually normal.

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.

Sleep researcher Yaron Dagan states that "[t]hese disorders can lead to harmful psychological and functional difficulties and are often misdiagnosed and incorrectly treated due to the fact that doctors are unaware of their existence."[1]

Types of circadian rhythm sleep disorders[edit]

Extrinsic type[edit]

One of these disorders is extrinsic (from Latin extrinsecus, from without, on the outside) or circumstantial:

Formerly,[2] Jet lag, too, was classified as an extrinsic type circadian rhythm disorder.

Intrinsic type[edit]

Four of them are intrinsic (from Latin intrinsecus, on the inside, inwardly), "built-in":

Normal circadian rhythms[edit]

Typical features of a normal cicadian rhythm, including a bedtime of 22:00.

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.[3]

Circadian rhythm abnormalities[edit]

Non-24-hour sleep–wake disorder 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 DSPD (Delayed sleep phase disorder), 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."[4]

Circadian rhythm abnormalities are also extremely commonly co-morbid with ADHD, especially in the form of sleep initiation insomnia. These have been genetically linked by findings of polymorphism in genes in common between those apparently involved in ADHD and those involved in the circadian rhythm[5][6] and a high proportion of DSPD among those with ADHD,[7][8] however no specific or further cause-effect relationship has been proven.

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.[9]

Treatment for circadian rhythm sleep disorders[edit]

Possible treatments for circadian rhythm sleep disorders include:

See also[edit]


  1. ^ Dagan, Yaron (February 2002). "Circadian rhythm sleep disorders (CRSD)" (Abstract). Sleep Medicine Reviews (Elsevier) 6 (1): 45–54. doi:10.1053/smrv.2001.0190. PMID 12531141. Retrieved 2010-10-13. 
  2. ^ "Highlights of Changes from DSM-IV-TR to DSM-5" (PDF). American Psychiatric Association. May 17, 2013. Retrieved May 23, 2013. 
  3. ^ National Institutes of Health. "Sleep - Information about Sleep". Retrieved 2007-01-28. 
  4. ^ Cataletto, Mary E.; Hertz, Gila (2005-09-07). "Sleeplessness and Circadian Rhythm Disorder" (Free registration required). eMedicine from WebMD. Retrieved 2008-07-20. 
  5. ^ A polymorphism at the 3′-untranslated region of the CLOCK gene is associated with adult attention-deficit hyperactivity disorder: American Journal of Medical Genetics Part B: Neuropsychiatric Genetics, Volume 147B, Issue 3, pages 333–338, 5 April 2008
  6. ^ “Adult attention-deficit hyperactivity disorder is associated with alterations in circadian rhythms at the behavioural, endocrine and molecular levels” - Molecular Psychiatry , (22 November 2011) doi:10.1038/mp.2011.149 (PubMed ID: 22105622 pre pub)
  7. ^ Van der Heijden KB, Smits MG, Van Someren EJ, Gunning WB (2005). "Idiopathic chronic sleep onset insomnia in attention-deficit/hyperactivity disorder: a circadian rhythm sleep disorder". Chronobiology International 22 (3): 559–70. doi:10.1081/CBI-200062410. PMID 16076654. 
  8. ^ - “About three-fourths of all adults with ADHD report inability to ‘shut off my mind so I can fall asleep at night’.”
  9. ^ First, Michael B. (2005). "New Diagnostic Codes for Sleep Disorders". American Psychiatric Association. Retrieved 2008-08-08. 
  10. ^ "Sleep Hygiene". Sleep Disorders Australia. 2006. p. 1. Retrieved 2011-12-09. 
  11. ^ "Resetting the Body Clock and Other research and insomniac treatment contacts". Flinders University. 2014. p. 1. Retrieved 2014-01-17. 
  12. ^ "Blue light has a dark side" online article from the May 2012 edition of Harvard Health Letter
  13. ^ Food and Drug Administration (January 31, 2014). "FDA approves Hetlioz: first treatment for non-24 hour sleep-wake disorder". FDA. 
  14. ^ The Cleveland Clinic Guide to Sleep Disorders by Nancy Foldvary-Schaefer, DO

External links[edit]