sleep-wake cycle

Non-24-hour sleep-wake syndrome

Non-24-hour sleep-wake syndrome is a rare and chronic circadian rhythm sleep disorder. The International Classification of Sleep Disorders, Chapter VI, Diseases of the Nervous System, defines the disorder as "a chronic steady pattern comprising one- to two-hour daily delays in sleep onset and wake times in an individual living in society." The pattern of delay persists literally "around the clock," typically taking a few weeks to complete one cycle. It affects less than 0.05% of the population (fewer than 1 in 2000 people), which means that it is classified as a "rare disease. Though most often referred to as Non-24, it is also known by the following terms:

Presentation

In people with this disorder, the body essentially insists that the day is longer 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 and hormone secretion. Left untreated, non-24-hour sleep-wake syndrome causes a person's sleep-wake cycle to change every day, the degree determined by how much over 24 hours the cycle lasts. The cycle may go around the clock, eventually returning to "normal" for one or two days before going "off" again. This is known as free-running sleep. Most cases that have been reported in the medical literature have occurred in blind patients. Sighted people with non-24 hour sleep-wake disorder do exist, but are much more rare and the etiology of their circadian disorder is less well understood. At least one case of a sighted person developing non-24 hour sleep-wake disorder was preceded by head injury; another patient diagnosed with the disorder was later found to have a "large pituitary adenoma that involved the optic chiasma. The problem, therefore, appears to be neurological. Specifically, it is thought to involve abnormal functioning of the suprachiasmatic nucleus of the hypothalamus.

There have, however, been several studies of sighted people with the syndrome. McArthur et al reported treating a sighted patient who "appeared to be subsensitive to bright light. In other words, the brain does not react normally to light (people with the disorder may or may not, however, be unusually subjectively sensitive to light; one study found that they were more sensitive than the control group). In 2002 Uchiyama et al examined five sighted Non-24 patients who showed, during the study, a sleep-wake cycle averaging 25.12 hours. That is appreciably longer than the 24.02 h average shown by the control subjects in that study, which was near the average innate cycle for healthy adults, younger and older, of 24.18 hours. The literature usually refers to a "one to two hour" delay per twenty four hour day (i.e. a 25-26 hour cycle).

Uchiyama et al had earlier determined that sighted Non-24 patients' minimum core body temperature occurs much earlier in the sleep episode than the normal two hours before awakening. They suggest that the long interval between the temperature trough and awakening, makes illumination upon awakening virtually ineffective. (See Phase response curve)

In their Clinical Review in 2007, Okawa and Uchiyama reported that people with Non-24 have a mean habitual sleep duration of nine to ten hours and that their circadian periods average 24.8 hours.

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.

Most people with this disorder find that it severely impairs their ability to function socially and occupationally. Typically, they are "partially or totally unable to function in scheduled social activities on a daily basis, and most are unable to work at conventional jobs. 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, to the point of falling into microsleeps, as well as myriad effects associated with acute and chronic sleep deprivation.

Treatment

Common treatments for non-24-hour sleep-wake syndrome are similar to those for delayed sleep phase syndrome. They include light therapy with a full spectrum lamp giving—usually—10000 lux, chronotherapy, acupuncture, hypnotics and/or stimulants (to promote sleep and wakefulness, respectively) and melatonin supplements. Light therapy has been shown useful in treating DSPS; effects on patients with Non-24 are less clear. Melatonin administration has been shown to be effective for mild cases of Non-24, particularly among the blind. It often takes several treatments before any progress is noticed, and for many the treatments may only be marginally effective or not effective at all. In addition, the treatment is not a cure, and the condition may only be managed.

Bright light therapy combined with the use of melatonin as a chronobiotic (see phase response curve, PRC) may be the most effective treatment. However the timing of both is tricky and a lot of determination and experimentation is usually necessary.

References

See also

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