Circadian rhythm sleep-wake disorders refer to a group of conditions in which the timing of sleep is affected. Circadian rhythms are often referred to as the body’s internal clock or the biological clock. Individuals with a circadian rhythm sleep-wake disorder are unable to naturally go to sleep or wake up at the time necessary for their work, school, or social environments.
The circadian rhythm sleep-wake disorders listed in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) include delayed sleep phase type, advanced sleep phase type, irregular sleep-wake type, non-24-hour sleep-wake type, and shift-work type. A diagnosis of a circadian rhythm sleep-wake disorder is only given if the sleep disturbance causes clinically significant distress or impairs an individual’s ability to function in social, occupational, or educational settings.
Circadian rhythm sleep-wake disorders all lead to excessive sleepiness or insomnia, or both. The following symptoms pertain to each of the circadian rhythm sleep-wake disorder subtypes, per the DSM-5.
The delayed sleep phase type is a sleep pattern in which a person falls asleep two or more hours after they intend to. As a result, they have difficulty waking in the morning and are excessively sleepy in the first part of the day. When people with this type of circadian rhythm disorder are able to set their own schedule, the quality and duration of their sleep are normal. Symptoms typically begin in adolescence and early adulthood and continue for months or years before a diagnosis is established.
The advanced sleep phase type of circadian rhythm sleep-wake disorder is characterized by sleep and waking times that are several hours earlier than desired or customary times. People with this condition fall asleep two or more hours before their desired sleep time and consequently experience early morning insomnia and excessive sleepiness throughout the day. It’s common for individuals with the advanced sleep phase type of circadian rhythm disorder to be known as “morning people,” and they will continue to wake early, even if they are required to stay up late.
The irregular sleep-wake type is a condition in which people do not have a clear circadian rhythm, and their sleep is fragmented into at least three periods during the 24-hour day. Individuals with this type of circadian rhythm disorder typically have insomnia at night and excessive sleepiness or napping during the day, and as a result they do not have one main period of sleep. This condition is most commonly seen in people with neurodegenerative disorders, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease.
The non-24-hour sleep-wake type of circadian rhythm sleep-wake disorder is a condition in which a person’s natural circadian rhythm does not align with the 24-hour day. People with this condition may experience insomnia or excessive sleepiness depending on the time of day or night and where their natural circadian rhythm is at that time. They may have periods of no symptoms when their natural sleep phase is aligned with the conventional time for sleep. These periods of being asymptomatic do not last, however, because their natural sleep phase will continue to drift later into the night until their sleep time will become daytime. Non-24-hour sleep wake type is most commonly seen among blind or visually impaired people who have decreased light perception.
The shift work type of circadian rhythm sleep-wake disorder is diagnosed based on a history of working outside of the normal 8:00 A.M. to 9:00 P.M. daytime window on a regularly scheduled basis. Individuals with the shift work type of circadian rhythm sleep-wake disorder consistently experience excessive sleepiness at work and have difficulty sleeping at home. Symptoms typically improve or disappear when a person resumes a daytime work routine.
There are no established genetic factors that predispose individuals to developing a circadian rhythm sleep-wake disorder, but symptoms of some such disorders, such as advanced sleep phase type, may have an earlier onset and be more severe among people with a family history of circadian rhythm sleep-wake disorders. Light exposure also plays a role in developing some circadian rhythm disorders. For example, hypersensitivity to evening light may predispose an individual to developing delayed sleep phase type of circadian rhythm sleep-wake disorder.
Treatment options for a circadian rhythm sleep-wake disorder depend on the type of disorder and the impact it is having on an individual’s quality of life. Behavior therapy strategies include maintaining consistent sleep-wake times, avoiding naps, exercising regularly, and avoiding stimulating substances (coffee, nicotine) and activities near bedtime. People with delayed sleep phase type should minimize exposure to light in the evening by keeping lights in their home dim and avoiding bright screens. Those with advanced sleep phase type should increase light exposure in the evenings by keeping lights on in their home.
Bright Light Therapy is a treatment option offered by sleep specialists to advance or delay sleep. Medications such as melatonin and short-term sleep aids can also be used to adjust sleep-wake time to a desired schedule.