Circadian Rhythm Disorders

Circadian Rhythm Disorders: Basics - Rhythm & Blues

• Master Clock: Suprachiasmatic Nucleus (SCN) in anterior hypothalamus.
  • Receives crucial light input via Retinohypothalamic Tract (RHT).
  • Light is the most potent zeitgeber (time-giver).
• Key Hormones & Rhythms:
  • Melatonin: From pineal gland; ↑ levels promote sleep; light suppresses its release.
  • Cortisol: From adrenal cortex; ↑ levels promote wakefulness; peaks in early morning.
  • Core Body Temperature: Follows a circadian pattern, typically lowest in early morning, rises during day.
• Entrainment: Process of synchronizing the internal biological clock to external environmental cues, primarily the light-dark cycle.

⭐ The Suprachiasmatic Nucleus (SCN) in the anterior hypothalamus is the principal circadian pacemaker, receiving direct input from the retina via the retinohypothalamic tract.

Circadian Rhythm Disorders: Types - Outta Sync Squad

• Delayed Sleep-Wake Phase Disorder (DSWPD)
  • Timing: 'Night owls'; sleep onset/offset delayed >2h.
  • Prevalence: Adolescents.
  • Associations: Genetic (hPER3, CRY1).
• Advanced Sleep-Wake Phase Disorder (ASWPD)
  • Timing: 'Morning larks'; sleep onset/offset advanced >2h.
  • Prevalence: Older adults.
  • Associations: Genetic (hPER2, CK1δ).
• Irregular Sleep-Wake Rhythm Disorder (ISWRD)
  • Timing: Disorganized; ≥3 sleep episodes/24h.
  • Associations: Neurodegenerative (Alzheimer's), institutionalization.
• Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD)
  • Timing: Free-running, cycle typically >24h; progressive daily delay.
  • Prevalence: Common in totally blind individuals.
  • Associations: Lack of light entrainment.

⭐ Over 50% of totally blind individuals experience Non-24-Hour Sleep-Wake Rhythm Disorder due to lack of photic entrainment.

📌 Mnemonic: Delay All Internal Naps (DSWPD, ASWPD, ISWRD, N24SWD).

Circadian Rhythm Disorders: Extrinsic & Dx - Travel & Toil Troubles

• Jet Lag Disorder:
  • Mismatch: internal clock vs. new time zone (rapid trans-meridian travel).
  • Symptoms: Insomnia, excessive daytime sleepiness (EDS), GI upset.
  • Eastward travel (phase advance) harder than westward (phase delay). 📌 "East is a beast, West is best".
• Shift Work Disorder (SWD):
  • Insomnia/EDS due to work schedule conflicting with habitual sleep times.
  • Affects 10-40% of shift workers.

Diagnosis of CRSDs:

• Clinical Interview: Detailed sleep-wake history.
• Sleep Diaries: Subjective record for ≥2 weeks.
• Actigraphy: Objective rest-activity patterns.

  ⭐ Actigraphy is a valuable objective tool for assessing sleep-wake patterns over several weeks in suspected CRSDs.

• Questionnaires: E.g., Morningness-Eveningness Questionnaire (MEQ), Munich ChronoType Questionnaire (MCTQ).

Circadian Rhythm Disorders: Treatment - Timing is Everything

• Goal: Align internal clock with desired sleep-wake cycle. Key is TIMING.
• Light Therapy (Phototherapy):
  • 2,500-10,000 lux bright light.
  • Morning light: Advances phase (e.g., DSWPD).
  • Evening light: Delays phase (e.g., ASWPD).
• Melatonin:
  • DSWPD: 0.5-5 mg, 1-5 hours before desired bedtime.
  • N24SWD: Daily at fixed time.
  • Jet Lag: Timed by travel direction.
• 📌 BAM: Bright light in AM for DSWPD (Advance); Melatonin in PM.
• Chronotherapy:
  • Progressive shift of sleep schedule (e.g., DSWPD: delay bedtime 1-3 hrs/day).
  • ⚠️ High adherence needed.
• Behavioral: Strict sleep hygiene, scheduled sleep, meals, exercise.
• Pharmacotherapy (Adjunctive): Hypnotics (short-term), Modafinil (Shift Work Disorder).

⭐ For Delayed Sleep-Wake Phase Disorder (DSWPD), appropriately timed evening melatonin (e.g., 0.5-1 mg, 3-5 hours before desired sleep onset) and morning bright light exposure are first-line treatments.

High‑Yield Points - ⚡ Biggest Takeaways

• DSWPD ("Night owls"): Delayed sleep phase. Treat: evening melatonin, morning light.
• ASWPD ("Morning larks"): Advanced sleep phase. Treat: morning melatonin, evening light.
• N24SWD: Common in totally blind individuals; tasimelteon is specific.
• Jet Lag Disorder: After travel across ≥2 time zones; melatonin at target bedtime.
• Shift Work Disorder: Due to night/rotating shifts; modafinil for alertness.
• ISWRD: Disorganized sleep, seen in dementia (e.g., Alzheimer's).
• Key tools: Sleep diary, actigraphy for diagnosis; melatonin, light therapy for management_._