In circadian rhythm disorders, endogenous sleep-wake rhythms (body clock) and the external light-darkness cycle become misaligned (desynchronized). The cause may be internal (eg, delayed or advanced sleep phase syndrome) or external (eg, jet lag, shift work). Circadian rhythm sleep disorders may occur in patients with Alzheimer disease or Parkinson disease and in patients who have had head trauma or encephalitis.
If the cause is external, other circadian body rhythms, including temperature and hormone secretion, can become out of sync with the light-darkness cycle (external desynchronization) and with one another (internal desynchronization); in addition to insomnia and excessive sleepiness, these alterations may cause nausea, malaise, irritability, and depression. Risk of cardiovascular and metabolic disorders may also be increased.
Repetitive circadian shifts (eg, due to frequent long-distance travel or rotating shift work) are particularly difficult to adapt to, especially when the shifts change in a counterclockwise direction. Counterclockwise shifts are those that shift awakening and sleeping times earlier (eg, when flying eastward, when rotating shifts from days to nights to evenings). Symptoms resolve over several days or, in some patients (eg, older patients), over a few weeks or months, as rhythms readjust. Because light is a strong synchronizer of circadian rhythms, exposure to bright light (sunlight or artificial light of 5,000 to 10,000 lux intensity) after the desired awakening time and the use of sunglasses to decrease light exposure before the desired bedtime speed readjustment. Melatonin before bedtime may help.
Patients with circadian rhythm disorders often misuse alcohol, hypnotics, and stimulants.
Circadian rhythm disorders include the following:
Jet lag disorder is caused by rapid travel across> 2 time zones. Eastward travel (advancing the sleep cycle) causes more severe symptoms than westward travel (delaying sleep).
If possible, travelers should gradually shift their sleep-wake schedule before travel to approximate that of their destination, and after arriving in the new locale, they should maximize exposure to daylight (particularly in the morning) during the day and exposure to darkness before bedtime. Short-acting hypnotics and/or wake-promoting drugs (eg, modafinil) may be used for brief periods after arrival.
Severity of symptoms is proportional to the
Fixed-shift work (ie, full-time night or evening) is preferable; rotating shifts should go clockwise (ie, day to evening to night). However, even fixed-shift workers have difficulties because daytime noise and light interfere with sleep quality, and workers often shorten sleep times to participate in social or family events.
Shift workers should maximize their exposure to bright light (sunlight or, for night workers, specially constructed bright artificial lightboxes) at times when they should be awake and ensure that the bedroom is as dark and quiet as possible during sleep. Wearing sunglasses during the morning commute home in anticipation of sleep is also useful. Sleep masks and white-noise devices are helpful. Melatonin before bedtime can also help. When symptoms persist and interfere with functioning, judicious use of hypnotics with a short half-life and wake-promoting drugs is appropriate.
In these syndromes, patients have normal sleep quality and duration with a 24-hour circadian rhythm cycle, but the cycle is out of sync with desired or necessary wake times. Less commonly, the cycle is not 24 hours, and patients awaken and sleep earlier or later each day. If able to follow their natural cycle, patients have no symptoms.
Delayed sleep phase syndrome: Patients consistently go to sleep and awaken late (eg, 3 am and 10 am). This pattern is more common during adolescence. If required to awaken earlier for work or school, excessive daytime sleepiness results; patients often present because school performance is poor or they miss morning classes. They can be distinguished from people who stay up late by choice because they cannot fall asleep earlier even if they try. Mild phase delay (< 3 hours) is treated by progressive earlier arising plus morning bright light therapy, perhaps with melatonin 4 to 5 hours before the desired bedtime. An alternative method is to progressively delay bedtime and awakening time by 1 to 3 hours/day until the correct sleep and wake times are reached.
Advanced sleep phase syndrome: This syndrome (early to bed and early to rise) is more common among older people and responds to treatment with bright light in the evening and light-preventing goggles in the morning.
Non–24-hour sleep-wake syndrome: Much less common, this syndrome is characterized by a free-running sleep-wake rhythm. The sleep-wake cycle commonly remains constant in length but is > 24 hours, resulting in a delay of sleep and wake times by 1 to 2 hours each day. This disorder is more common among blind people. Tasimelteon, a melatonin receptor agonist, can increase nighttime sleep duration and decrease daytime sleep duration in totally blind patients who have this disorder. The dose is 20 mg orally once a day before bedtime, at the same time every night.
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