Circadian Rhythm Sleep Disorder (Sleep–Wake Schedule Disorders)

Circadian Rhythm Sleep Disorder (Sleep–Wake Schedule Disorders)

Circadian rhythm disturbances result from a mismatch between the internal or endogenous circadian sleep–wake system and the external or exogenous demands on the sleep–wake system. The individual’s tendency to sleep–wakefulness does not match that of her or his social circumstances or of the light–dark cycle. Al-though some individuals do not find this mismatch to be a prob-lem, for others the circadian rhythm disturbance interferes with the ability to function properly at times when alertness or sleepi-ness is desired or required. For those individuals, insomnia, hy-persomnia, sleepiness and fatigue result in significant discomfort and impairment. The circadian rhythm disturbances include de-layed sleep phase, advanced sleep phase, shift work, jet lag and non-24-hour-day syndrome.

Diagnosis

The diagnosis is based on a careful review of the history and circadian patterns of sleep–wakefulness, napping, alertness and behavior. According to DSM-IV criteria, the diagnosis of circadian rhythm sleep disorder requires significant social or occupational impairment or marked distress related to the sleep disturbance. It is often useful for patients with chronic com-plaints to keep a sleep–wake diary covering the entire 24-hour day each day for several weeks. If possible, an ambulatory device that measures rest–activity, such as a wrist actigraph, might supplement the sleep–wake diary. Wrist actigraphs record acceleration of the wrist at frequent intervals, such as every minute, and save it for later display. Because the wrist is mostly at rest during sleep, the record of wrist rest–activity provides a fairly accurate estimate of the timing and duration of sleep–wakefulness. In addition, some commercial wrist activ-ity devices have a built-in photometer, which provides a record of ambient light–darkness against which the rest–activity pat-tern can be compared.

Delayed and Advanced Sleep Phase Disorders

Delayed sleep phase refers to a delay in the circadian rhythm in the sleep–wake cycle. These individuals are generally not sleepy until several hours after “normal” bedtime (i.e., 2–3 AM). If allowed to sleep undisturbed, they will sleep for 7 or 8 hours, which means they awaken at 10 to 11 AM. People with delayed sleep phase are considered extreme “owls”. They may or may not complain of sleep-onset insomnia. They usually enjoy their alertness in the evening and night and have little desire to sleep beginning at 10 PM or midnight. Their problem is trying to wake up at normal times (i.e., 6–7 AM). In essence, their rhythm is shifted to a later clock time relative to conventional rest–activity patterns.

Individuals with delayed sleep phase often choose careers that allow them to set their own schedules, such as freelance writ-ers. Delayed sleep phase occurs commonly in late adolescence and young adulthood, such as in college students. As many of these individuals age, however, their endogenous sleep–wake rhythm advances and they eventually are able to conform them-selves to a normal rest period at night.

For others, however, this phase shift of the endogenous os-cillator may lead at a later age to the advanced sleep phase. In this condition, individuals become sleepy earlier in the evening (e.g., 7–8 PM). They will also sleep for 7 to 8 hours, but that means they awaken at 2 to 3 AM. These individuals are” “larks”, being most alert in the morning. They complain of sleep maintenance insom-nia, that is, they cannot stay asleep all night long. This condition is more prevalent in the elderly than in the young.The etiology of extreme “night owls” and “larks” is probably multifaceted but, in some cases, appears to reflect genetic factors

Treatment

Clinical management includes chronobiological strategies to shift the phase position of the endogenous circadian oscillator in the appropriate direction. For example, exposure to bright light in the morning advances the delayed sleep phase, that is, indi-viduals will become sleepy earlier in the evening. On the other hand, administration of bright light in the evening acts to delay the circadian rhythm, that is, individuals will become sleepy later in the evening. Light is usually administered in doses of 2500 lux for a period of 2 hours per day, although the ideal intensity and duration are yet to be determined. For some individuals, spend-ing more time outdoors in bright sunlight may be sufficient to treat the sleep phase. For example, individuals with delayed sleep phase should be encouraged to remove blinds and curtains from their windows, which would allow the sunlight to pour into their bedrooms in the morning when they should arise. In addition, gradual adjustments of the timing of the sleep–wake cycle may be used to readjust the phase position of the circadian oscillator. For example, patients with delayed phase disorder can be advised to delay the onset of sleep by 2 to 3 hours each day (i.e., from 4 to 7 to 10 AM, and so on) until the appropriate bedtime. After that, they should maintain regular sleep–wake patterns, with exposure to bright light in the morning.