Diagnosis and Management of Clinical Conditions Affected by Disturbances in the Wake-Sleep Cycle
Core concepts
This domain concerns circadian rhythm sleep-wake disorders and the consequences of misaligned or insufficient sleep on other diseases: delayed sleep-wake phase disorder, advanced sleep-wake phase disorder, shift work disorder, jet lag, irregular sleep-wake rhythm, non-24-hour sleep-wake rhythm (common in blind individuals), and the effects of sleep loss on obesity, diabetes, hypertension, cardiovascular disease, mood, cognition, and seizure control. The candidate must understand circadian biology (light as the dominant zeitgeber, melatonin as a phase marker) and the two-process model of sleep regulation.
Management anchors
Timed bright-light exposure and strategically timed melatonin are the workhorses. Delayed phase: morning bright light plus low-dose melatonin in the early evening. Advanced phase: evening bright light plus morning melatonin. Shift work: scheduled light exposure, strategic napping, and caution with hypnotics; modafinil/armodafinil are options for shift work disorder. Jet lag: eastward travel is harder; use light and melatonin aligned to destination time. Non-24-hour rhythm in blindness: melatonin at a fixed clock time. Always pair circadian therapy with sleep hygiene and, where indicated, CBT-I.
Traps
Questions test directionality: light and melatonin must be timed to advance versus delay the clock, and getting the direction wrong is the classic error. Another trap is attributing daytime sleepiness in a shift worker to a primary hypersomnia without first addressing the schedule. Remember that circadian disorders are diagnoses of timing, not of sleep quantity; PSG is not required and is usually normal. Also recognize that sleep restriction worsens glycemic control and blood pressure, so sleep is part of chronic disease management.
Rule of thumb
To advance the clock (make sleep earlier), give morning light and evening melatonin; to delay it, reverse both.