Circadian Rhythm Sleep Wake Disorders

The timing of sleep is determined by actions of our ‘body clock’ (Circadian Rhythm). Alterations of the Circadian Rhythm can cause various sleep complaints, of which the best known is ‘jet lag’. Patients may experience insomnia at night, excessive sleepiness in the daytime, or irregular periods of sleep and wake through the 24 hour day.

We take it for granted that we stay awake in the day and sleep at night. However, to bring this about we need to have an “internal clock” – a “biological clock” – and a mechanism to synchronise it with the “external clock”. This physiological system is known as the circadian system. Circadian rhythm sleep disorders occur when there is a mismatch between an individual’s internal time and the external time.

The main factor determining the timing of sleep is the circadian rhythm. Individuals with a functioning circadian clock would have one major sleep episode in a given 24 hour period, usually between 9 PM and 7 AM. This time window is known as the ‘sleep phase’. When one sleeps at a later time the sleep phase is said to be delayed. If one sleeps at an earlier time the sleep phase is said to be advanced. If the time of onset of sleep is delayed on successive days the pattern is known as ‘non-24 hour’ (previously known as ‘free-running ‘pattern). If there is no functioning circadian rhythm, individuals sleep for short periods on multiple occasions in a 24 hour period. This is known as irregular sleep-wake pattern.

There are six major types of the Circadian Rhythm Sleep-wake Disorders which are listed below.

Delayed sleep-wake phase disorder (DSWPD)
Advanced sleep-wake phase disorder (ASWPD)
Irregular sleep-wake rhythm disorder (ISWRD)
Non-24 hour sleep-wake rhythm disorder (N24SWD)
Shift work disorder (SWD)
Jetlag disorder

Delayed Sleep-Wake Phase Disorder (DSWPD):

In DSWPD, the sleep phase is delayed in relation to the desired sleep and wake-up time. Patients with this condition experience difficulty in falling asleep at a ‘normal’ bedtime. This often gives rise to a complaint of sleep-onset insomnia. The morning wake-up time is delayed accordingly. If woken up In the morning, such individuals finds it difficult to ‘come round’ and feels sleepy in their wake time. They feel more awake later the day and are at their best in the evenings.

The exact cause of DSWPD is not known but several mechanisms are proposed. These include behavioural and physiological factors.

Individual preference is a major factor in some cases particularly when bedtimes and wake times are not enforced. In adolescence there is a normal delay in the timing of circadian rhythms. This is worsened by late evening activities such as doing homework, watching TV and using the Internet. Staying up late and waking up late in the morning can result in delay in sleep. Light exposure later in the evening may worsen phase delay. DSWPD may run in families. It has also been observed after traumatic brain injury.

DSWPD can affect people of all ages but most commonly occurs in teenagers and young adults. Roughly 7% of people struggle to fall asleep until very late at night and have difficulty getting out of bed in the morning. They may have significant problems with getting up in time to go to school, going to work and may struggle with daytime sleepiness. This may make it difficult to function adequately in family and society.

Advanced Sleep Wake Phase Disorder (ASWPD):

People with ASWPD start feeling sleepy in the early evening. They often wake up too early and cannot go back to sleep. Symptoms may go unrecognized as ASWPD rarely interferes with life except for social events or business meetings in the early evening.

Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD)

When the body clocks does not synchronise with the terrestrial clock, the timing of sleep is not regular. Instead, sleep onset is delayed on successive days. This delay varies from about 30 minutes to over one hour. Such patients are said to have a Non-24 Hour Sleep-Wake Rhythm Disorder (N24SWD) This condition usually occurs in individuals who are completely blind. Occasionally it can occur in sighted individuals when it is known as “Sighted Non-24 Sleep-Wake- Rhythm Disorder”.

This condition mostly occurs in individuals who are completely blind. Occasionally it can occur in sighted individuals when it is known as “Sighted Non-24 Sleep-Wake- Rhythm Disorder”. In sighted individuals Delayed Sleep-Wake Phase Disorder often precede N24SWD . There is often a history of decreased exposure to light and structured social and physical activity. In sighted people the disorder can be induced by certain environmental conditions such as decreased or inappropriately timed exposure to circadian entraining agents particularly light.

Irregular Sleep-Wake Rhythm Disorder

Occasionally individuals may lose the circadian rhythm for sleep altogether. It is then known as irregular sleep-wake with rhythm disorder (ISWRD) patients with this condition tend to have several short episodes of sleep throughout the 24 hour period. This can manifest as ‘insomnia’ at night and ‘excessive sleep’ in the day time.

Shift Work Disorder:

20% of workers in any industrialised society work at night. Night Work causes workers to get less sleep during the day than day workers who sleep at night. Night shift worker’s sleep is often patchy because the brain is set to be awake during the daytime. People who work rotating shifts often have difficulty getting enough sleep, since adjusting to the changing work schedule can be quite challenging. This leads to “Shift-work disorder”, a common problem that is usually ignored by workers and employers.

Jet-lag Disorder:

is a common sleep problem that we take in our stride. It occurs whenever someone travels across several time zones. In jet-lag, our ”body-clock” is out of synchrony with external time. Symptoms include indigestion, daytime sleepiness, insomnia, poor concentration, and irritability. Some people can adjust quickly, but others need many days to adjust.

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