A 32-year-old man comes to the physician complaining of excessive sleepiness for the past several months. He reports falling asleep while dealing with customers and had a near accident when he fell asleep while driving. The patient reports that he occasionally hears voices while falling asleep and finds himself "temporarily frozen" and unable to move upon awakening. Which of the following is the most appropriate treatment for this patient?

Continuous positive airway pressure

All of the following factors are involved in altered patterns of hormone release except

Lights on throughout 24 hours of the day

In which of the following conditions would the cortisol level be highest?

Normal person in the early morning

Normal person after receiving dexamethasone

Normal person in the late evening

Which factor best predicts response to light therapy in SAD?

Chronotype/Morningness-eveningness preference

In comparison to a normal healthy person, in the evening time, which of these will have an elevated ACTH as well as elevated Cortisol?

Transient state after exercise (evening time)

Normal healthy person (evening time)

Circadian Rhythm Disorders for FMGE: High-Yield Physiology Lessons

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.

Phase Response Curves to Light and Melatonin

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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