Misalignment between endogenous circadian rhythms and the light/dark cycle can result in circadian rhythm sleep disorders, such as:
- delayed sleep timing (DSPD)
- advanced sleep timing (advanced sleep phase disorder)
- erratic sleep timing (irregular sleep/wake rhythm)
- complete dissociation from the light/dark cycle (circadian rhythm sleep disorder, free-running type).
These 4 conditions are thought to involve predominantly intrinsic mechanisms, but circadian dysrhythmias also can be induced by exogenous factors. Extreme work schedules or rapid travel across time zones can challenge the circadian system’s ability to acclimate and the individual’s ability to achieve a desired sleep schedule.17
Differential diagnosis
Because DSPD relates primarily to an aberration in timing of sleep, it is characterized as a disorder only if the individual’s preferred schedule interferes substantially with social or occupational functioning. The International Classification of Sleep Disorders (ICSD) provides detailed diagnostic criteria (Table).17
Table
Diagnostic criteria for delayed sleep phase disorder
A. Delay exists in the phase of the major sleep period in relation to desired sleep time and wake-up time, as evidenced by:
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| B. When allowed to choose a preferred schedule, patients exhibit normal sleep quality and duration for age and maintain a delayed but stable phase of entrainment to the 24-hour sleep/wake pattern. |
| C. Monitoring with a sleep log or actigraphy (including sleep diary) for at least 7 days demonstrates a stable delay in the timing of the habitual sleep period. |
| D. The sleep disturbance is not better explained by another sleep disorder, medical or neurologic disorder, mental disorder, medication use, or substance use disorder. |
| Source: Adapted and reprinted with permission from International classification of sleep disorders. Diagnostic and coding manual. 2nd ed17 |
Depression and anxiety often manifest with sleep difficulties, as do inadequate sleep hygiene and other conditions associated with prolonged sleep initiation. According to ICSD criteria, primary insomnia can be differentiated from DSPD if the patient readily initiates and maintains sleep when allowed to sleep on his/her desired sleep/wake schedule. Accumulated evidence has largely debunked this notion, however, as polysomnographic studies have demonstrated both prolonged sleep latency and impaired sleep efficiency in DSPD patients versus matched controls.3
Assessment tools can complement the clinical history in diagnosing DSPD. Either a sleep log or actigraphy is required to demonstrate a stable phase delay, but actigraphy typically generates more reliable data.18 Actigraphs are compact “motion detectors” whose output while being worn by patients allows longitudinal assessment of sleep/wake parameters.
Eveningness tendencies of presumptive DSPD patients can be further verified with the Morningness-Eveningness Questionnaire (MEQ) (Box 2).19 Low scores are associated with evening types—felt to correspond to the endogenous circadian period—and can help narrow the differential diagnosis of sleep-initiation complaints.20
A morning or evening person? A self-assessment questionnaire
The Morningness-Eveningness Questionnaire (MEQ) developed by Horne and Ostberg19 can be used to verify eveningness tendencies of patients with presumptive delayed sleep phase disorder. The MEQ is a 19-item self-assessment tool with responses that are assigned values totaling up to 86 points. Examples of the questions include:
- Considering only your own ‘feeling best’ rhythm, at what time would you get up if you were entirely free to plan your day?
- Considering only your own ‘feeling best’ rhythm, at what time would you go to bed if you were entirely free to plan your day?
- How easy do you find it to get up each day?
- When you have no commitments the next day, how much later do you go to bed compared to your usual bedtime?
- One hears about ‘morning’ and ‘evening’ types of people. Which ONE of these types do you consider yourself to be?
Lower scores are associated with evening types—felt to correspond to the endogenous circadian period—and can help in narrowing the differential diagnosis of sleep-initiation complaints.20 Scores on the MEQ are interpreted as:
- 70 to 86: definite morning type
- 59 to 69: moderately morning type
- 42 to 58: neither type
- 31 to 41: moderately evening type
- 16 to 30: definite evening type
CASE CONTINUED: ‘Definite evening type’
Jason scores 28 on the MEQ, consistent with a “definite evening type.” Actigraphic monitoring is scheduled during a school holiday, when he is instructed to sleep according to his preferred schedule with the least possible restriction.
A clearly delayed sleep phase is evident, with the habitual sleep period occurring between 5 AM and 1 PM. Even on days when he was quite sleep-restricted because of an enforced wake time, sleep onset on the ensuing evening was substantially delayed, suggesting an obligate nature for the delayed sleep/wake schedule. Overall, Jason had few complaints with respect to impaired alertness while on this unrestricted schedule and experienced a much more stable mood.