Circadian Rhythm Sleep-Wake Disorders

CRSWD Fundamentals - Body Clock 101

• Circadian Rhythm: Endogenous ~24-hour biological clock; regulates sleep-wake, hormones, body temperature.
• Suprachiasmatic Nucleus (SCN): Master pacemaker in hypothalamus; receives light signals via retinohypothalamic tract.
• Melatonin: Pineal gland hormone; secretion ↑ in darkness, ↓ in light; promotes sleep. Serotonin is its precursor.
• Zeitgebers: External cues ("time-givers") entraining the SCN.
  • Primary: Light (most potent).
  • Others: Meals, social activity, exercise, temperature.

⭐ The SCN's intrinsic rhythm is genetically determined and persists for a period even without external light cues (free-running rhythm).

Intrinsic CRSWDs - Phase Shifts & Free Runs

Intrinsic CRSWDs: Alterations in endogenous circadian pacemaker.

• Delayed Sleep-Wake Phase Disorder (DSWPD): "Night owls".
  • Sleep onset/offset delayed ≥2 hrs. Difficulty waking, daytime sleepiness.
  • Tx: Morning Bright Light Therapy (BLT), evening low-dose melatonin.
• Advanced Sleep-Wake Phase Disorder (ASWPD): "Morning larks".
  • Sleep onset/offset advanced ≥2 hrs. Early sleepiness/awakening.
  • Common in elderly. Familial ASWPD (PER2, CSNK1D genes).
  • Tx: Evening BLT, early AM melatonin.
• Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD): "Free-running".
  • Rhythm not 24-hr entrained (typ. 24.2-25 hrs). Progressive daily drift.
  • Common in blind (no light entrainment).

  ⭐ N24SWD in blind individuals often presents with cyclical insomnia and daytime sleepiness that waxes and wanes over weeks.

  • Tx: Melatonin (e.g., 0.5 mg), Tasimelteon.
• Irregular Sleep-Wake Rhythm Disorder (ISWRD):
  • Fragmented sleep; ≥3 sleep bouts/24 hrs. No main sleep period; weak rhythm.
  • Assoc: Neurodegeneration (Alzheimer's), TBI.
  • Tx: Structured routine, light, activity, melatonin.

Extrinsic CRSWDs - Travel & Work Woes

• Jet Lag Disorder (JLD)
  • Cause: Circadian misalignment; rapid travel across ≥ 2 time zones.
  • Symptoms: Insomnia/excessive sleepiness, daytime fatigue, impaired function.
  • Eastward travel (phase advance) worse than westward (phase delay). 📌 "East is a beast".
  • Self-limiting.
• Shift Work Disorder (SWD)
  • Cause: Work schedule (e.g., night shifts) conflicts with endogenous circadian rhythm.
  • Symptoms: Insomnia/excessive sleepiness, fatigue, ↑accident risk, health issues.
  • Affects ~10-40% of shift workers.
• Management Focus
  • Timed light & melatonin.
  • Strategic naps (SWD).
  • Hypnotics (JLD); Modafinil (SWD).

⭐ Eastward travel generally causes more severe jet lag as it requires a phase advance of the body clock, which is harder than a phase delay from westward travel.

CRSWD Toolkit - Setting Clocks Right

• Diagnostic Tools:

  • Sleep Diary: Patient-recorded sleep-wake times, naps, daily habits.
  • Actigraphy: Wrist-watch like device; objectively measures rest/activity cycles over 1-2 weeks.
  • Polysomnography (PSG): Primarily to rule out other sleep disorders if suspected.

• Management Strategies: Goal: Align internal clock with desired schedule.

  • Light Therapy (Phototherapy):
    • Exposure to bright light (2,500-10,000 lux).
    • Timing is key: 📌 AM light for Advance (e.g., DSWPD); PM light to Postpone/delay (e.g., ASWPD).
  • Melatonin:
    • Low dose (0.3-0.5 mg) for phase-shifting; higher doses (1-5 mg) for hypnotic effect.
    • Timing: DSWPD: ~3-5 hrs before desired bedtime. ASWPD: Morning (use cautiously).
  • Chronotherapy:
    • Systematic, progressive adjustment of sleep schedule (e.g., delaying bedtime by 1-2 hrs/day for DSWPD).
  • Behavioral Strategies: Strict sleep hygiene, scheduled sleep-wake times.

⭐ In Delayed Sleep-Wake Phase Disorder (DSWPD), appropriately timed melatonin (0.5 mg, 3-5 hours before desired sleep) can effectively advance the sleep phase.

High‑Yield Points - ⚡ Biggest Takeaways

• Delayed Sleep-Wake Phase Disorder (DSWPD): "Night owls", sleep onset/offset delayed ≥2 hours; common in adolescents.
• Advanced Sleep-Wake Phase Disorder (ASWPD): "Morning larks", sleep onset/offset advanced ≥2 hours; common in older adults.
• Non-24-Hour Sleep-Wake Rhythm Disorder: Free-running rhythm (cycle >24h), often in totally blind individuals due to absent light entrainment.
• Irregular Sleep-Wake Rhythm Disorder: Lacks a clear circadian pattern; associated with neurodegenerative conditions like Alzheimer's.
• Shift Work Disorder: Insomnia or excessive sleepiness linked to work schedule conflicting with natural circadian rhythm.
• Jet Lag Disorder: Sleep disturbance after rapid travel across ≥2 time zones.
• Management often involves light therapy (e.g., for DSWPD), melatonin, and behavioral strategies; actigraphy aids diagnosis.