Circadian Rhythm Disorders - Body's Master Clock
- Suprachiasmatic Nucleus (SCN): Hypothalamic master clock; primary pacemaker.
- Input: Light (main zeitgeber) via retinohypothalamic tract (RHT).
- Output: Governs sleep-wake, melatonin, cortisol, body temperature rhythms.
- Core Molecular Clock: Involves CLOCK, BMAL1, PER, CRY genes (feedback loop).
- Melatonin: Pineal hormone; ↑ in darkness (promotes sleep), ↓ by light.
- Cortisol: Peaks early morning.
⭐ The SCN generates a free-running rhythm of ~24.2 hours, entrained daily by light to 24 hours.
Circadian Rhythm Disorders - Rhythm Wreckers
Disruptions in the internal body clock lead to various disorders, impacting sleep timing and quality.
| Disorder | Core Feature & Typical Profile | Key Management Strategies |
|---|---|---|
| DSWPD (Delayed) | "Night owls"; sleep/wake significantly delayed. Adolescents. | Evening melatonin, Morning light therapy. |
| ASWPD (Advanced) | "Morning larks"; sleep/wake significantly early. Older adults. | Evening light therapy, Afternoon melatonin. |
| N24SWD (Non-24-Hour) | Free-running rhythm, often >24h. Common in blind. | Tasimelteon, Melatonin. |
| ISWRD (Irregular) | Fragmented sleep; no clear day/night pattern. Neurodegenerative. | Structured routine, Light therapy, Melatonin. |
| Jet Lag Disorder | Clock vs. new time zone mismatch. Trans-meridian travel. | Timed melatonin, Light exposure, Short hypnotics. |
| Shift Work Disorder | Insomnia/sleepiness with work schedule. Night/rotating shifts. | Modafinil, Naps, Timed light, Melatonin. |
Circadian Rhythm Disorders - Clock Detectives
Misalignment: internal clock vs. external schedule. Leads to sleep issues & daytime dysfunction.
- Core Types:
- DSWPD: Delayed Sleep-Wake Phase. "Night owls". Sleep onset >2hrs late.
- ASWPD: Advanced Sleep-Wake Phase. "Morning larks". Early sleep/wake.
- ISWRD: Irregular Sleep-Wake Rhythm. Fragmented, no clear pattern.
- N24SWD: Non-24-Hour. Free-running (often blind). Cycle >24hrs.
- SWD: Shift Work Disorder.
- JLD: Jet Lag Disorder.
- Detection Tools:
- Clinical Interview: Key for history.
- Sleep Diary: ≥2 weeks, patient-reported.
- Actigraphy: Objective motor activity patterns.
- Management: Timed light, melatonin, chronotherapy.
⭐ DSWPD is the most common CRSWD in adolescents and young adults, often presenting as difficulty initiating sleep.
Circadian Rhythm Disorders - Time Tamers
- Misalignment: internal clock vs. external cues (zeitgebers).
- Types:
- DSWPD (Delayed Sleep-Wake Phase Disorder): "Night owls"; sleep onset/offset persistently delayed ≥2 hrs.
- ASWPD (Advanced Sleep-Wake Phase Disorder): "Morning larks"; sleep onset/offset persistently advanced ≥2 hrs.
- ISWRD (Irregular Sleep-Wake Rhythm Disorder): Fragmented sleep; no main sleep period; often in neurodegenerative conditions.
- N24SWD (Non-24-Hour Sleep-Wake Rhythm Disorder): Free-running cycle, typically >24 hrs; common in totally blind individuals.
- Shift Work Disorder: Insomnia or excessive sleepiness linked to work schedule.
- Jet Lag Disorder: Symptoms after rapid travel across ≥2 time zones.
- Diagnosis: Clinical history, sleep diary, actigraphy.
- Management Strategies:
| Disorder | Light Therapy (Timing) | Melatonin (Timing; Dose) | Other Key Approaches |
|---|---|---|---|
| DSWPD | Morning (2500-10000 lux) | Evening (3-5h pre-desired sleep; 0.5-5 mg) | Chronotherapy (delay) |
| ASWPD | Evening | Morning (low dose, if needed) | Chronotherapy (advance) |
| N24SWD | Morning (if light perception) | Evening (consistent time; 0.5-5 mg); Tasimelteon | Scheduled sleep/dark |
| ISWRD | ↑Daytime exposure, ↓Evening light | Evening (low dose) | Structured routines |
| Shift Work | Pre-shift / Post-shift (day sleep) | Before daytime sleep (1-3 mg) | Anchor sleep, strategic naps |
| Jet Lag | Destination: Eastbound AM, Westbound PM | Destination PM (dose varies) | Gradual adaptation |
High‑Yield Points - ⚡ Biggest Takeaways
- SCN in hypothalamus: master circadian clock.
- Melatonin (pineal): induces sleep; light suppresses its secretion.
- DSWPD ("Night owls"): sleep late; treat with morning bright light, evening melatonin.
- ASWPD ("Morning larks"): sleep early; treat with evening bright light.
- N24SWD: common in totally blind individuals; free-running rhythm; treat with melatonin or tasimelteon.
- Jet Lag Disorder: worse with eastward travel (requires phase advance).
- Shift Work Disorder: due to atypical work hours; manage with planned sleep, light exposure, and melatonin strategically.
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