Non-24-hour sleep-wake disorder
| Non-24-hour sleep–wake disorder | |
|---|---|
| Classification and external resources | |
| Specialty | neurology |
| ICD-10 | G47.24 |
| ICD-9-CM | 327.34 |
| MeSH | D021081 |
Non-24-hour sleep–wake disorder (non-24), is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in society." Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light/dark cycle in nature.
The sleep pattern can be quite variable. People with a circadian rhythm that is quite near to 24 hours may be able to sleep on a conventional, socially acceptable schedule, that is, at night. Others, with a "daily" cycle upwards of 25 hours or more may need to adopt a sleep pattern that is congruent with their free-running circadian clock, shifting their sleep times daily, thereby often obtaining satisfactory sleep but suffering social and occupational consequences.
The majority of people with non-24 are totally blind, and the failure of entrainment is explained by an absence of photic input to the circadian clock. These people's brains may have normal "body clocks", but the clocks do not receive input from the eyes about environmental light levels, as that requires a functioning retina, optic nerve and visual processing center.
The disorder also occurs in sighted people for reasons that are not well understood. Their circadian rhythms are not normal, often running to more than 25 hours. Their visual systems may function normally but their brains are incapable of making the large adjustment to a 24-hour schedule.
Though often referred to as non-24, for example by the FDA, the disorder is also known by the following terms:
The disorder in its extreme form is an invisible disability that can be "extremely debilitating in that it is incompatible with most social and professional obligations".
In people with non-24, the body essentially insists that the length of a day (and night) is appreciably longer (or, very rarely, shorter) than 24 hours and refuses to adjust to the external light–dark cycle. This makes it impossible to sleep at normal times and also causes daily shifts in other aspects of the circadian rhythms such as peak time of alertness, body temperature minimum, metabolism and hormone secretion. Non-24-hour sleep–wake disorder causes a person's sleep–wake cycle to move around the clock every day, to a degree dependent on the length of the cycle, eventually returning to "normal" for one or two days before "going off" again. This is known as free-running sleep.
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Wikipedia