Circadian Rhythm Sleep-Wake Disorders
What Are Circadian Rhythm Disorders?
Circadian rhythm sleep disorders are associated with a dysfunction of our internal biological clock. They occur when there is a mismatch between the sleep-wake cycle required by our environment, and our own internal sleep-wake cycle.
The term ‘circadian’ is derived from the latin word circa, which means ‘around’, and diēm, which means ‘the day’. Therefore, circadian means ‘around the day.’
There are 7 different types of circadian rhythm disorders, as listed by the International Classification of Sleep Disorders (ICSD-3):
- Delayed sleep-wake phase disorder
- Advanced sleep-wake phase disorder
- Irregular sleep-wake rhythm disorder
- Non-24 hour sleep-wake rhythm disorder
- Shift work disorder
- Jet lag disorder
- Circadian sleep-wake disorder not otherwise specified (NOS)
The suprachiasmatic nucleus (SCN) is a region of the brain that is responsible for regulating circadian rhythms. The SCN is composed of a group of cells that that respond to light and dark stimuli. This tiny region can be found in the hypothalamus – just above the optic chiasm.
Light travels down the optic nerve of the eye and makes its way to the SCN. When it reaches the SCN it lets our internal body clock know whether or not we should be awake. The SCN is also responsible for the regulation of other biological processes, such as body temperature and hormone levels.
When light is detected by the SCN there are several things that occur:
- Body temperature rises;
- There is a production of hormones (i.e. cortisol) and;
- There is an inhibition of hormones (i.e. melatonin)
Melatonin is a hormone that is associated with sleep. It is released by the pineal gland when the SCN detects darkness. Melatonin levels rise in the evening, and remain at an elevated level throughout the night.
There are several treatment options available for circadian rhythm disorders:
- Behavioural therapy
- Bright-light therapy
You may be required to undergo behavioural therapy, which looks to maintain regular sleep-wake times.
Several medication options exist for circadian rhythm sleep disorders:
- Melatonin receptor stimulant (i.e. Rozerem)
Circadian rhythm disorders can be caused by a variety of different things, such as:
- Shift work
- Travelling (change in time zone)
- Certain medication
- Lifestyle changes
- Neurological disorders (i.e. Alzheimer’s, or Parkinson’s disease)
The diagnosis of a circadian rhythm disorder is performed using the patient’s clinical history, and other information such as sleep logs and actigraphic recordings.
Anctigraphic recordings are taken using an actigraph unit (actimetry sensor), which is a non-invasive way to monitor the individuals rest/activity cycles. The actgraph unit is typically worn around the wrist and is the similar in size to a watch. The device should be worn for at least 7 days, but it is preferred to be worn for 14 days to include both working and non-working days. 
According to the International Classification of Sleep Disorders (ICSD-3) the criteria for circadian rhythm sleep disorders are:
- A chronic or recurrent pattern of sleep-wake rhythm disruption due primarily to alteration of the endogenous circadian timing system or misalignment between the endogenous circadian rhythm and the sleep-wake schedule desired or required by an individual’s physical environment or social/work schedules
- The circadian rhythm disruption leads to insomnia symptoms, excessive sleepiness or both
- The sleep and wake disturbances cause clinically significant distress or impairment in mental, physical, social, occupational, educational or other important areas of functioning.
(ALL criteria A-C must be met)
- Bassetti, C, Dogas, Z, Peigneux, P., 2014. Sleep Medicine Textbook. 1st ed. Regensburg: European Sleep Research Society (ESRS).
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