Circadian Rhythm Sleep Disorder (CRSD)

Circadian Rhythm Sleep DisorderCircadian Rhythm Sleep Disorder (CRSD) includes several sleep disorders characterized by the disturbed sleep.


Circadian rhythms (derived from Latin “around the day”)  are also known as the body’s biological clock (“internal body clock”) that regulates the everyday 24-hours cycle activity of the person and  body processes (body temperature control, hormone levels in the blood and etc.). Circadian rhythms also control the ability of the person to remain awake during the day and helps to fall asleep at night. Circadian rhythms are also influenced by the regime of the  person, working hours and schedule.

Affected people have difficulties while falling asleep or are unable to remain awake and active during the daytime. However, the quality of sleep fulfills the normal quality.

Causes and risk factors

Circadian Rhythm Sleep Disorder are caused by the alterations of the central 24-hours time-keeping system, the impairment of the inner  circadian rhythm and the environmental factors.
The disruption of the circadian rhythms may be associated with the following:

  • Pregnancy
  • Shift work
  • Irregular timetable
  • Time zone changes (jet lag)
  • Medications
  • Changes in routine such as staying up late or sleeping in
  • Medical problems and mental disorders including Alzheimer’s or Parkinson disease

See also: Sleep Apnea


The group of circadian rhythm sleep disorder is divided into two subgroups: extrinsic and intrinsic types.

Extrinsic type

(derived from Latin extrinsecus, from without, on the outside) or circumstantial. This subgroup includes only one disorder:

  • Shift work sleep disorder affects who works in shifts during the night or with the changeable timetable;


Intrinsic type
 (from Latin intrinsecus, on the inside, inwardly), “built-in”include:

  • Advanced sleep phase disorder (ASPD), advanced sleep phase syndrome (ASPS), the person is unable to stay awake in the evening (early goes to sleep) and faces difficulties with staying asleep (is awake earlier than he/she wants) in the morning. Affected individuals are commonly called “morning larks”. The complaints usually include of early waking up and the feeling of sleepiness early in the evening.
  • Delayed sleep phase disorder (DSPD,  delayed sleep phase syndrome (DSPS), is connected with a severe disturbance of sleep timing. Affected people experience a period of peak alertness at the night (insomnia), frequently, until 2 a.m. or later, that results in the latter falling to sleep and difficulties waking up in time and interferes with social engagements, work, school etc. Sometimes the affected people may be called the “night owls”.
  • Irregular sleep–wake rhythm characterized by sleeping irregularly, usually more than twice per day. However, the total time of sleep is typical as for the person’s age.
  • Non-24-hour sleep–wake disorder (non-24,  hypernychthemeral syndrome), is common for totally blind persons. Affected individuals fall asleep later and later each day, so that the period of peak alertness is also changing every day. Therefore the whole cycle of sleep and wakefullness is disturbed. As the result the time of sleep and its quality reduces and a person may feel sleepy during the day.
  • Jet Lag or Rapid Time Zone Change Syndrome is common for those who travel across time zones. The disorder is caused by a difference between the body’s biological clock and the regime of a new time zone. People experience excessive sleepiness and lack of alertness during the daytime(Circadian Rhythm Sleep Disorder).

All the affected individuals experience also anxiety and depression, tiredness and fatigue.


The diagnosis is based on a detailed history; a sleep dairy and/or wrist actigraphy for at least 7 days is also indicated.


Circadian Rhythm Sleep DisorderThe treatment of sleep disorders varies according to the type of the disorder. The main goal is to change the person’s pattern of sleep and create the schedule.
Treatment may include:

  • Behavior therapy: maintaining regular sleep-wake times, avoiding daytime sleep, regulation of everyday routine, avoiding caffeine, nicotine, stimulating activities (especially during several hours before going to bed), minimizing the exposure to light in the evening and reducing the time of work at the computer of avoiding late watching the TV.
  • Bright light therapy is used to treat ASPD or DSPD. This therapy helps to reset the circadian clock. The high intensity light (10,000 lux) is used during 1-2 hours.
  • Chronotherapy implies a progressive change (1 to 2 hours per day) of sleep time.


Applicable medicines

Melatonin, wake-promoting agents, and short-term sleep may be prescribed.

The dose of melatonin varies from 0.3 mg (difficulties falling asleep) up to 3.0 mg (insomnia) and even 5.0 mg (for blind persons) depending on the severity of the person’s condition.

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