Circadian Rhythm Disorder
 

Chronic circadian rhythm sleep disorders are internal abnormalities of the circadian rhythms, the body's internal clock. They arise when a person is unable to fall asleep at a normal bedtime (late evening), although he/she is able to sleep at other times.  The length of the internal circadian cycle can normally be a bit shorter or longer than 24 hours.  The cycle is entrained to 24 hours by external factors, especially light.  If it cannot be entrained, either because it is too far afield of the normal range, or for other neurological reasons, the result is a circadian disorder.  In these disorders, the internal coordination of the various rhythms may also be normal or faulty.  For example, some hormones may be on a different cycle than others.

Common to these disorders is inflexibility: even when physically tired or sleep deprived, sufferers cannot make up for lost sleep outside of their hard-wired sleep times.  This factor is generally misunderstood by people who do not suffer from these disorders, leading to misunderstanding of what sufferers are up against, and a conclusion that they are just lazy or haven't tried hard enough to live on a normal schedule.

 

The International Classification of Diseases (ICD-10-CM, 2014) lists 6 subtypes of circadian rhythm sleep disorder:

  • Delayed sleep phase type.
  • Free-running type.
  • Advanced sleep phase type.
  • Irregular sleep-wake type.
  • Shift work type.
  • Jet lag type.
  • As well as unspecified, other, and conditions specified elsewhere.

The DSM-V defines Circadian Rhythm Sleep-Wake Disorder as follows:

A persistent or recurrent pattern of sleep disruption that is primarily due to an alteration of the circadian system or to a misalignment between the endogenous circadian rhythm and the sleep-wake schedule required by an individual's physical environment or social or professional schedule.  The sleep disruption leads to excessive sleepiness or insomnia, or both.   The sleep disturbance causes clinically significant distress or impairment in social, occupational, and other important areas of functioning.