Circadian rhythm sleep-wake disorders — structured clinical viva

Two CRSWD phenotypes: DSWPD in the student (free-day recovery delayed sleep) and shift work disorder in the nurse (day insomnia + night sleepiness with driving risk). Neither is managed as generic primary insomnia alone; both need phase/schedule-based care and safety planning.[2][5][6]

1. Classification. Intrinsic: DSWPD, ASWPD, non-24, ISWRD (Auger AASM 2015). Extrinsic: shift work, jet lag. Student = DSWPD; nurse = SWD. Mention non-24 if blindness and free-running appear.[1][2]

2. Mechanisms. SCN master clock; melanopsin light input; two-process model (S + C). PRC: morning light advances, evening light delays; melatonin roughly opposite. DLMO as phase marker.[2]

3. Discriminators. DSWPD vs insomnia: good sleep if free delayed schedule. Reduced need + elevated mood = mania, not DSWPD. SWD vs voluntary preference: clinical insomnia/sleepiness with impairment on rostered nights. Screen OSA/substances.[6]

4. Assessment. Diary 1–2 weeks; actigraphy; occupational/driving risk (nurse near-miss risk is urgent); mood/ADHD; substances. PSG not routine for pure CRSWD.[2]

5. DSWPD management. Fixed rise, morning light, dark evenings, strategically timed melatonin (Sletten: 0.5 mg ~1 h before desired bedtime + behavioural scheduling). Avoid random nightcap dosing. BAP supports circadian-specific approaches.[3][6]

6. SWD management. Remove from driving if unsafe tonight; planned naps, strategic caffeine, timed light, dark day-sleep environment. Modafinil 200 mg has RCT support for night sleepiness (Czeisler) but is not a complete normaliser and does not replace duty removal when already dangerous. Organisational roster liaison. Drake-order ~10% of night/rotating workers meet SWD criteria.[4][5]

7. Bonus non-24. Totally blind free-running → tasimelteon SET/RESET pathway / specialist entrainment.[7]