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.
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 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
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.
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