Common subtypes

• Delayed Sleep‑Wake Phase Disorder (DSPD): habitual sleep onset and wake times are delayed relative to desired times (typical in adolescents/young adults).
• Advanced Sleep‑Wake Phase Disorder (ASPD): sleep onset and wake times are earlier than desired (common in older adults).
• Non‑24‑Hour Sleep–Wake Rhythm Disorder (Non‑24): circadian rhythm free‑runs, causing progressively later sleep times — frequent in blind individuals with absent light perception.
• Irregular Sleep–Wake Rhythm Disorder (ISWRD): fragmented sleep across 24 hours with no clear main sleep period — seen in neurocognitive disorders.
• Shift Work Disorder (SWD): sleep and wake disruption related to work schedules causing insomnia or excessive sleepiness.
• Jet Lag Disorder: transient circadian misalignment after rapid travel across time zones causing sleep disturbance and daytime impairment.

Key symptoms & impact

• Difficulty initiating sleep or waking at socially required times, daytime sleepiness, impaired concentration, mood disturbance and reduced occupational/academic performance.
• Safety risks: increased motor vehicle accidents, workplace errors—especially in shift workers and those with excessive sleepiness.

Assessment checklist

1. Sleep history: habitual sleep–wake times, variability, work/social schedule, light exposure, caffeine/alcohol/tobacco, and timing of symptoms.
2. Use 1–2 weeks sleep diary and actigraphy to document phase, total sleep time and fragmentation; consider longer monitoring for non‑24 or irregular patterns.
3. Screen for comorbid sleep disorders (OSA, RLS), psychiatric disorders (depression, bipolar) and medical contributors.
4. Assess circadian markers when available (dim light melatonin onset — DLMO) for precise phase measurement in specialist settings.
5. Evaluate impact: driving risk, occupational functioning, academic performance and quality of life.

Diagnostic clues by subtype

• DSPD: long sleep latency at conventional times, normal sleep when allowed to follow preferred schedule, adolescent onset common.
• ASPD: early evening sleepiness and very early morning awakening with preserved sleep quality.
• Non‑24: progressively shifting sleep times and periods of relative alignment; consider in totally blind patients.
• ISWRD: highly fragmented sleep with multiple naps and no main consolidated sleep period; common in dementia.
• SWD: symptoms tied to work schedule with improvement during days off or holiday; variable depending on shift type.

Management principles

1. Light therapy: timed bright light exposure (10,000 lux for 20–30 min commonly) to advance or delay circadian phase — morning light advances, evening light delays. Tailor timing to desired phase shift and consider spectacles/boxes validated for clinical use.
2. Melatonin & melatonin agonists: low‑dose melatonin (0.5–3 mg) given in the evening (for phase advance) or strategically timed before desired sleep can shift the circadian clock—use timing based on DLMO when available. Tasimelteon is licensed for non‑24 in some jurisdictions.
3. Behavioral strategies: strict sleep–wake scheduling, controlled exposure to light (blue‑light avoidance in evening), sleep hygiene, limiting naps and sleep restriction where appropriate.
4. Chronotherapy: systematic delay of sleep time (gradual or planned) to reset phase—use cautiously and under specialist guidance due to risk of non‑adherence and social disruption.
5. Shift work interventions: schedule design (forward‑rotating shifts), strategic light and dark exposure, naps before night shifts, caffeine judiciously timed, and employer accommodations where possible.
6. Safety advice: counsel regarding driving and high‑risk tasks when symptomatic; consider temporary work modification or medical leave for severe cases.

Pharmacologic notes & cautions

• Melatonin is generally well tolerated but timing is critical—incorrect timing may worsen misalignment.
• Stimulants/wake‑promoting agents (modafinil, armodafinil) can reduce daytime sleepiness in SWD but do not treat underlying circadian misalignment—use with caution and specialist oversight.
• Benzodiazepines/z‑drugs may help sleep initiation but can worsen circadian adaptation and are not recommended as primary treatment for CRSWDs.

Special populations

• Adolescents: DSPD is common—school start time adjustments, light therapy and behavioural interventions are helpful.
• Blind individuals: high risk of non‑24—offer melatonin/tasimelteon and specialist support for entrainment strategies.
• Older adults and dementia: ISWRD management focuses on structured daytime activity, light exposure, and treatment of comorbid sleep disorders.

Key takeaways

• Identify subtype using sleep diary and actigraphy; target treatment to shift the circadian clock (timed light, melatonin) plus behavioural strategies.
• Timing is everything—incorrect timing of light or melatonin can worsen symptoms; consider specialist testing (DLMO) for complex cases.
• Address safety (driving, work), coordinate with employers/schools for accommodations and refer to sleep medicine when first‑line measures fail or risks are high.