Non-24-hour sleep-wake syndrome

Non-24-hour sleep-wake syndrome, also termed circadian rhythm sleep disorder - free-running type, circadian arrhythmia, non-24-hour circadian rhythm disorder or hypernychthemeral syndrome, is a 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."

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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.

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."^[1] In 2002 Uchiyama et al examined five sighted Non-24 patients who showed, during the study, a sleep-wake cycle averaging 25.12 hours.^[2] 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.^[3] 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 virtually ineffective.^[4] (See Phase response curve)

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.

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, and melatonin supplements. 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.

Treatment with melatonin taken 30 minutes to two hours before the desired bedtime may be helpful. Too high a dose of melatonin may have the unintended effect of disturbing the sleep or even causing nightmares, and uncontrollable yawning the next day. Bright light therapy combined with the use of melatonin may be the most effective treatment. The timing of both is tricky and a lot of determination and experimentation is usually necessary.

References

See also

• Delayed sleep phase syndrome
• Advanced sleep phase syndrome
• Circadian rhythm sleep disorder