Circadian Rhythm Sleep-Wake Disorders
Framework
Circadian rhythm sleep-wake disorders arise from misalignment between the endogenous clock and the external environment or from altered clock function. Key types: delayed sleep-wake phase disorder (common in adolescents), advanced sleep-wake phase disorder (common in older adults), irregular sleep-wake rhythm (dementia, institutionalized patients), non-24-hour sleep-wake rhythm (frequently in totally blind individuals), shift-work disorder, and jet-lag disorder.
Assessment
Diagnosis relies on history plus a sleep diary and actigraphy (typically 1-2 weeks); dim-light melatonin onset or core body temperature can estimate phase but is not routine. Distinguish circadian misalignment from insomnia and from insufficient sleep: in delayed phase, sleep is normal in duration and quality if the person can sleep on their preferred schedule.
Treatment
Timed bright-light exposure and strategically timed melatonin shift phase. Light in the morning advances phase; light in the evening delays it. Melatonin taken in the evening advances phase; taken in the morning it delays. For delayed phase disorder: morning bright light plus evening low-dose melatonin and gradual advance of sleep time. For advanced phase: evening bright light. For non-24-hour rhythm in blind patients: timed melatonin. Shift-work disorder management includes strategic napping, caffeine, and planned light exposure; hypnotics are not first-line.
Traps
Direction of shift is the classic trap: evening light delays, morning light advances. Also avoid labeling a night owl as having insomnia without checking the sleep diary, and remember that melatonin timing (not dose) drives the phase effect.
Rule of thumb
"Morning light advances, evening light delays; evening melatonin advances, morning melatonin delays."