Sleep-Wake and Circadian Rhythm Disorders
What you must know
Circadian rhythm sleep-wake disorders (CRSWDs) include delayed sleep-wake phase disorder (DSWPD), advanced sleep-wake phase disorder (ASWPD), shift work disorder, jet lag, non-24-hour sleep-wake rhythm disorder, and irregular sleep-wake rhythm. Diagnosis hinges on a mismatch between the endogenous circadian phase and the desired/required schedule, with consequent insomnia and/or daytime impairment.
Key biology: light is the dominant zeitgeber; morning light advances phase, evening light delays it. Melatonin is a chronobiotic-evening melatonin advances phase, morning melatonin delays it. Core body temperature minimum (CBTmin) is a practical phase marker.
Traps
- Confusing DSWPD with insomnia: DSWPD patients sleep well when allowed to follow their delayed schedule.
- Misapplying melatonin timing: giving melatonin in the morning worsens DSWPD.
- Forgetting that non-24 is common in totally blind patients (no light entrainment).
- Assuming shift work disorder requires abnormal sleep architecture; it is a clinical diagnosis.
Rule of thumb
"Light in the morning advances; light in the evening delays." For DSWPD: morning bright light + evening melatonin + fixed wake time. For ASWPD: evening bright light.
Worked example
A 22-year-old cannot fall asleep until 3 a.m. and sleeps until noon, but sleeps 8 hours when unconstrained. This is DSWPD, not insomnia. Treat with morning bright light, low-dose evening melatonin 3-5 hours before desired bedtime, and gradual 15-minute bedtime advances.