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Circadian Rhythm Sleep-Wake Disorder
Circadian Rhythm Sleep-Wake Disorders (CRSDs) involve a problem in the timing of sleep. Sleep is disrupted due to a misalignment between the body’s internal rhythm and the individual’s desired sleep-wake cycle. People with CRSDs are not able to fall asleep when they want or be as fully awake as they wish or need to be. This problem may stem from internal/bodily or external/ environmental factors. It is estimated that 35 million Americans suffer from CRSDs.
What Are Circadian Rhythms?
Circadian rhythms are 24-hour rhythms that control human sleep and other bodily functions. “Circadian” stems from the Latin circa diem meaning “about a day.” Sleep and wakefulness are controlled in part by an “internal clock” located in a region of the brain called the suprachiasmatic nucleus (SCN). As the body’s master clock, the SCN sends out signals that change the levels of hormones (e.g., melatonin and cortisol) and body temperature over a 24-hour period. Regular exposure to light and dark are necessary to synchronize the internal clock with the external day. Bright light (e.g., sunlight) received by the eye and projected to the SCN resets the clock every morning to keep it on a regular daily schedule. If the clock does not receive the light and dark signals at the right times, it malfunctions, producing hormones at the wrong time of day. Over time, this can result in insomnia at night and excessive sleepiness during the day, potentially causing serious distress and impaired functioning. Recent research suggests that certain wavelengths of light in the blue range are most responsible for regulating the circadian cycle. This finding has led to novel ways to reduce light exposure at critical times (see Light Avoidance below).
There are five different CRSD types. In all types, the sleep schedule differs from the conventional pattern and is often a cause for concern.
Delayed Sleep Phase Disorder (DSPD)
People with DSPD have a sleep schedule that is timed much later than usual or desired. Their preference is to stay up late into the night and wake up in the late morning or early afternoon. If they are unable to maintain this preferred schedule, they will have symptoms including difficulty falling asleep, difficulty waking in the morning, and excessive morning sleepiness. DSPD is the most common CRSD. It can be present at any age, but is seen most frequently in adolescents and young adults (affecting up to 16% of this population), often interfering with school and work. DSPD involves more extreme behavior than the natural tendency of people in their teens and 20s to stay up late and sleep late. (This young person’s night-owl pattern can often be changed by consistently using a fixed wake-up time and other good sleep habits—see Sleep Hygiene below).
The increase in LED lighting and, especially, electronic screens in laptops, smartphones, and some e-readers has added late-night bright lights to the environment of many individuals. This bright light suppresses the normal se-cretion of melatonin in the evening and may exacerbate DSPD.
Advanced Sleep Phase Disorder (ASPD)
ASPD is characterized by sleeping times that are several hours earlier than usual or desired. People with ASPD generally go to sleep between 6 and 9 p.m. and wake up between 2 and 5 a.m. Symptoms of ASPD include late day sleepiness and early morning insomnia. ASPD may impair cognitive functioning, social interactions, and personal safety, especially at the end of the day. About 1% of middle-aged adults suffer from it, and it increases with age. A family history of ASPD is common in people with the disorder.
Irregular Sleep-Wake Disorder (ISWD)
ISWD is the absence of a regular sleep pattern. There is no major sleep period, and sleep is fragmented into a series of naps over each 24-hour period. People with ISWD generally display short periods of sleep across the day with the longest stretch (usually shorter than 4 hours) occurring sometime between 2 and 6 a.m. Symptoms of ISWD also include insomnia or excessive sleepiness, depending on time of day. ISWD is most commonly associated with neurological disorders (e.g., dementia, developmental delay), traumatic brain injury, and some medical and psychiatric conditions in which there is social isolation and/or lack of light and structured activities in the conventional daytime.
Non-24-Hour Sleep-Wake Disorder (Non-24)
Non-24 is most common among blind persons who have no light perception (impacting about half of these individuals). It has sometimes been observed with severe psychiatric disorders. Classic symptoms include cyclic insomnia in which individuals will cycle between insomnia and normal sleep for weeks or months. However, many individuals with Non-24 may always have poor sleep as they try, and fail, to get back into a more regular sleep pattern.
Shift Work Disorder (SWD)
SWD is seen in persons who work the night shift or who have frequently changing work shifts. In affected individuals, these work patterns cause the sleep-wake schedule to be out of synch with the body’s internal rhythms, leading to insomnia when trying to sleep during the day and excessive sleepiness when trying to be awake at work at night. About 25% of shift workers (or 5% of the U.S. workforce) suffer from SWD. What’s worse is that SWD may lead to other psychiatric and medical problems.
Therapists assess CRSDs by collecting a detailed history of the problem using sleep questionnaires, sleep diaries (in which the patient tracks daily sleep information such as into and out-of bed times), a wrist sensor (actigraph) that measures sleep indirectly through wrist movement, and interviews with the person. Medical and psychiatric problems are also evaluated, and treatment can be recommended at this time, too. Patients are screened for primary sleep disorders, such as Obstructive Sleep Apnea, which may lead to a recommendation for an overnight sleep study in a sleep lab. For some people, chronic insomnia may also play a part with CRSD in the problem and may require its own assessment and treatment (see Cognitive Behavior Therapy for Insomnia below.)