Delayed Sleep Phase Disorder (DSPD)
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:
- 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.
- 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.
- Patients have little or no reported difficulty in maintaining sleep once sleep has begun.
- Patients have a relatively severe to absolute inability to advance the sleep phase to earlier hours by enforcing conventional sleep and wake times.
- 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.
- 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.
- The symptoms do not meet the criteria for any other sleep disorder causing inability to initiate sleep or excessive sleepiness.
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.
- 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.
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. *