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Delayed sleep-phase disorder (DSPD), also known as delayed sleep-phase syndrome (DSPS) or delayed sleep-phase type (DSPT), is a circadian rhythm sleep disorder affecting the timing of sleep, peak period of alertness, the core body temperature rhythm, hormonal and other daily rhythms, compared to the general population and relative to societal requirements. People with DSPD generally fall asleep some hours after midnight and have difficulty waking up in the morning.
Often affected people report that while they do not get to sleep until the early morning they do fall asleep around the same time every day. Unless they have another sleep disorder such as sleep apnea in addition to DSPD, patients can sleep well and have a normal need for sleep. Therefore, they find it very difficult to wake up in time for a typical school or work day. If, however, they are allowed to follow their own schedules, e.g. sleeping from 4 a.m. to noon (04:00 to 12:00), they sleep soundly, awaken spontaneously, and do not experience excessive daytime sleepiness.
The syndrome usually develops in early childhood or adolescence. An adolescent version disappears in adolescence or early adulthood; otherwise DSPD is a lifelong condition. Depending on the severity, the symptoms can be managed to a greater or lesser degree, but there is no all-encompassing cure. Prevalence among adults, equally distributed among women and men, is approximately 0.15%, or 3 in 2,000. It is also genetically linked to ADHD by findings of polymorphism in genes in common between those apparently involved in ADHD and those involved in the circadian rhythm and a high proportion of DSPD among those with ADHD.
DSPD was first formally described in 1981 by Dr. Elliot D. Weitzman and others at Montefiore Medical Center. It is responsible for 7–10% of patient complaints of chronic insomnia. However, as few doctors are aware of it, it often goes untreated or is treated inappropriately; DSPD is often misdiagnosed as primary insomnia or as a psychiatric condition. DSPD can be treated or helped in some cases by careful daily sleep practices, light therapy, and medications such as melatonin and modafinil (Provigil); the former is a natural neurohormone responsible partly and in tiny amounts for the human body clock. At its most severe and inflexible, it is a disability.
According to the International Classification of Sleep Disorders (ICSD), the circadian rhythm sleep disorders share a common underlying chronophysiologic basis:
The major feature of these disorders is a misalignment between the patient's sleep pattern and the sleep pattern that is desired or regarded as the societal norm... In most circadian rhythm sleep disorders, the underlying problem is that the patient cannot sleep when sleep is desired, needed or expected.
The ICSD (page 128-133) diagnostic criteria for delayed sleep-phase disorder are:
1- There is an intractable delay in the phase of the major sleep period in relation to the desired clock time, as evidenced by a chronic or recurrent complaint of inability to fall asleep at a desired conventional clock time together with the inability to awaken at a desired and socially acceptable time.
2- When not required to maintain a strict schedule, patients will exhibit normal sleep quality and duration for their age and maintain a delayed, but stable, phase of entrainment to local time.
3- Patients have little or no reported difficulty in maintaining sleep once sleep has begun.
4- Patients have a relatively severe to absolute inability to advance the sleep phase to earlier hours by enforcing conventional sleep and wake times.
5- Sleep-wake logs and/or actigraphy monitoring for at least two weeks document a consistent habitual pattern of sleep onsets, usually later than 2 a.m., and lengthy sleeps.
6- Occasional noncircadian days may occur (i.e., sleep is "skipped" for an entire day and night plus some portion of the following day), followed by a sleep period lasting 12 to 18 hours.
7- The symptoms do not meet the criteria for any other sleep disorder causing inability to initiate sleep or excessive sleepiness.
8- If any of the following laboratory methods is used, it must demonstrate a delay in the timing of the habitual sleep period: 1) Twenty-four-hour polysomnographic monitoring (or by means of two consecutive nights of polysomnography and an intervening multiple sleep latency test), 2) Continuous temperature monitoring showing that the time of the absolute temperature nadir is delayed into the second half of the habitual (delayed) sleep episode.
Some people with the condition adapt their lives to the delayed sleep phase, avoiding common business hours (e.g., 9 a.m. to 5 p.m.) as much as possible. The ICSD's severity criteria, all of them "over at least a one-month period", are:
Mild: Two hour delay associated with little or mild impairment of social or occupational functioning.
Moderate: Three hour delay associated with moderate impairment.
Severe: Four hour delay associated with severe impairment.
Some features of DSPD which distinguish it from other sleep disorders are:
People with DSPD have at least a normal—and often much greater than normal—ability to sleep during the morning, and sometimes in the afternoon as well. In contrast, those with chronic insomnia do not find it much easier to sleep during the morning than at night.
People with DSPD fall asleep at more or less the same time every night, and sleep comes quite rapidly if the person goes to bed near the time he or she usually falls asleep. Young children with DSPD resist going to bed before they are sleepy, but the bedtime struggles disappear if they are allowed to stay up until the time they usually fall asleep.
DSPD patients can sleep well and regularly when they can follow their own sleep schedule, e.g. on weekends and during vacations.
DSPD is a chronic condition. Symptoms must have been present for at least one month before a diagnosis of DSPD can be made.
Attempting to force oneself onto daytime society's schedule with DSPD has been compared to constantly living with 6 hours of jet lag; DSPD has, in fact, been referred to as "social jet lag". Often people with DSPD manage only a few hours sleep a night during the working week, then compensate by sleeping until the afternoon on weekends. Sleeping in on weekends, and/or taking long naps during the day, may give people with DSPD relief from daytime sleepiness but may also perpetuate the late sleep phase.
People with DSPD can be called night owls. They feel most alert and say they function best and are most creative in the evening and at night. People with DSPD cannot simply force themselves to sleep early. They may toss and turn for hours in bed, and sometimes not sleep at all, before reporting to work or school. Less extreme and more flexible night owls, and indeed morning larks, are within the normal chronotype spectrum.
By the time those who have DSPD seek medical help, they usually have tried many times to change their sleeping schedule. Failed tactics to sleep at earlier times may include maintaining proper sleep hygiene, relaxation techniques, early bedtimes, hypnosis, alcohol, sleeping pills, dull reading, and home remedies. DSPD patients who have tried using sedatives at night often report that the medication makes them feel tired or relaxed, but that it fails to induce sleep. They often have asked family members to help wake them in the morning, or they have used several alarm clocks. As the disorder occurs in childhood and is most common in adolescence, it is often the patient's parents who initiate seeking help, after great difficulty waking their child in time for school.
The current formal name established in the second edition of the International Classification of Sleep Disorders is circadian rhythm sleep disorder, delayed sleep phase type; the preferred common name is delayed sleep-phase disorder.
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