Non-24-hour sleep–wake disorder
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Non-24-hour sleep–wake disorder (non-24[1] or N24SWD[2]) 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 a society".[3] Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light–dark cycle in nature. Although this sleep disorder is more common in blind people, affecting up to 70% of the totally blind,[4] it can also affect sighted people. Non-24 may also be comorbid with bipolar disorder, depression, and traumatic brain injury.[2] The American Academy of Sleep Medicine (AASM) has provided CRSD guidelines since 2007 with the latest update released in 2015.[2][5]
This article possibly contains original research. (November 2018) |
Non-24-hour sleep–wake disorder | |
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Other names | Hypernychthemeral syndrome, free-running disorder |
Specialty | Neurology |
Symptoms | Progressively shifting nighttime |
Complications | None if sleeping according to biological clock, sleep deprivation otherwise |
Duration | Lifetime |
Causes | Blindness for the blind, unknown cause for the sighted |
Diagnostic method | Sleep diary, actigraphy |
Treatment | Medication |
Medication | Tasimelteon, melatonin |
Frequency | 50–70% of totally (without light perception) blind people, less prevalent in sighted |
People with non-24 experience daily shifts in the circadian rhythm such as peak time of alertness, body temperature minimum, metabolism and hormone secretion. These shifts do not align with the natural light–dark cycle. 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. This is known as free-running sleep.[citation needed]
People with the disorder may have an especially hard time adjusting to changes in "regular" sleep–wake cycles, such as vacations, stress, evening activities, time changes like daylight saving time, travel to different time zones, illness, medications (especially stimulants or sedatives), changes in daylight hours in different seasons, and growth spurts, which are typically known to cause fatigue. They also show lower sleep propensity after total sleep deprivation than do normal sleepers.[6]
Non-24 can begin at any age, not uncommonly in childhood. It is sometimes preceded by delayed sleep phase disorder.[7]
Most people with this disorder find that it severely impairs their ability to function in school, in employment, and in their social lives. Typically, they are "partially or totally unable to function in scheduled activities on a daily basis, and most cannot work at conventional jobs".[3] Attempts to keep conventional hours by people with the disorder generally result in insomnia (which is not a normal feature of the disorder itself) and excessive sleepiness,[3] to the point of falling into microsleeps, as well as myriad effects associated with acute and chronic sleep deprivation. People with non-24 who force themselves to live to a normal workday "are not often successful and may develop physical and psychological complaints during waking hours, i.e. sleepiness, fatigue, headache, decreased appetite, or depressed mood. Patients often have difficulty maintaining ordinary social lives, and some of them lose their jobs or fail to attend school."[6]