What are circadian sleep disorders?

Updated: Oct 09, 2018
  • Author: Sufen Chiu, MD, PhD; Chief Editor: Caroly Pataki, MD  more...
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A circadian clock or oscillator located in the suprachiasmatic nuclei of the anterior hypothalamus influences the wakefulness or alertness phase. A circadian clock potentiates alternate or diurnal phases of the sleep-wake cycle. A free-running human sleep-wake cycle is 25 hours; however, the cycle entrained by the environment results in a 24-hour cycle.

In patients with circadian sleep disorders, sleep and associated processes are at opposite phases or periods. These disorders may represent a poor compensatory ability for sleep loss and include failure to adequately synchronize sleep-wake behaviors and adapt to environmental demands, such as school. They are frequently observed in adolescents with delayed sleep phase.

Circadian rhythm sleep-wake disorder as defined by DSM-5 is a persistent or recurrent pattern of sleep disruption that is primarily due to an alteration of the circadian system or to misalignment between the circadian rhythm and the sleep-wake schedule required. This sleep disruption leads to excessive sleepiness and/or insomnia. These symptoms cause significant impairment in functioning. Subtypes to be specified include the following:

  • Delayed Sleep Phase Type

  • Advanced Sleep Phase Type

  • Irregular Sleep-Wake Type

  • Non-24-Hour Sleep-Wake Type

  • Shift Work Type

  • Unspecified Type

The history usually consists of a delay in the timing of onset of sleep by more than 2 hours. When individuals are allowed to set their sleep schedule, sleep is normal in quality and duration. There is an increasing prevalence during adolescence, which may related to physiological and behavioral factors.

Some individuals may be hypersensitive to evening light, which delays their sleep onset. Others are hyposensitive to morning light and do not respond to the phase-advancing effects. There may be familial and sporadic forms involving mutations in circadian genes such as PER3 and CKIe.

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