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Lecture 5: International Classification of Sleep Disorders

Jun 26, 2025

Overview

This lecture provides an overview of the International Classification of Sleep Disorders (ICSD), covering its history, structure, and main diagnostic criteria for common sleep disorders.

Purpose and Evolution of Sleep Disorder Classification

  • Classifications help physicians recognize and diagnose specific diseases using defined criteria.
  • Sleep medicine is a young, evolving specialty that became independent in the late 20th century.
  • Significant milestones: discovery of REM sleep (1953), melatonin (1958), and brain sleep centers.
  • The first sleep disorder classification appeared in 1979, with official international versions following in 1990, 2005, and 2014 (ICSD-3).

Structure of ICSD-3

  • ICSD-3 organizes sleep disorders into six main chapters: Insomnia, Sleep-Related Breathing Disorders, Central Disorders of Hypersomnolence, Circadian Rhythm Sleep-Wake Disorders, Parasomnias, and Sleep-Related Movement Disorders.
  • Each disorder includes diagnostic criteria, clinical features, epidemiology, subtypes, and diagnostic methods.
  • Pediatric sleep issues are now integrated within each disorder rather than in a separate chapter.

Diagnostic Manuals

  • ICSD-3 is the primary reference for sleep disorders.
  • Additional manuals provide event-scoring rules for sleep studies (e.g., polysomnography).

Insomnia Disorders

  • Diagnosis requires: subjective sleep difficulty (initiation, maintenance, or early awakening), adequate opportunity to sleep, and negative daytime effects.
  • Distinction between acute (≤3 months) and chronic (>3 months; ≥3 times/week) insomnia.
  • Subtypes from previous editions have been merged in ICSD-3 due to overlapping features.

Sleep-Related Breathing Disorders

  • Includes obstructive and central sleep apnea, hypoventilation, and nocturnal hypoxemia.
  • Diagnosis relies on sleep study indices (AHI, RDI).
  • Severity: mild (RDI 5-15), moderate (15-30), severe (>30).
  • Central apneas are ≥50% of events; chain-stokes breathing is associated with heart failure.
  • Hypoventilation diagnosed by sustained CO₂ elevation during sleep.

Central Disorders of Hypersomnolence

  • Includes narcolepsy (type 1 with cataplexy/low orexin; type 2 without), idiopathic hypersomnia, Kleine-Levin syndrome, and insufficient sleep syndrome.
  • Diagnosis relies on sleep studies (MSLT with mean latency <8 min, ≥2 SOREMPs for narcolepsy).
  • Insufficient sleep syndrome results from chronic sleep deprivation, treatable by extending sleep time.

Circadian Rhythm Sleep-Wake Disorders

  • Caused by misalignment of internal (suprachiasmatic nucleus) and environmental cues.
  • Types include delayed/advanced sleep phase, irregular rhythm, non-24-hour (often in blind), shift work, and jet lag.
  • Diagnosis via actigraphy and melatonin profiling (DLMO).
  • Treatment uses light therapy and melatonin timing.

Parasomnias

  • Abnormal behaviors during sleep; classification depends on sleep stage (NREM or REM).
  • NREM: confusional arousals, sleepwalking, sleep terrors.
  • REM: REM behavior disorder, sleep paralysis, nightmares.
  • Other: sleep-related hallucinations, exploding head syndrome, enuresis.

Sleep-Related Movement Disorders

  • Main disorders: Restless Legs Syndrome (RLS) and Periodic Limb Movement Disorder (PLMD).
  • RLS: sensory urge to move legs, worse at rest, relieved by movement, evening worsening.
  • PLMD: repetitive limb movements during sleep, common in RLS.
  • Also includes bruxism, leg cramps, sleep myoclonus, and others.

Miscellaneous Sleep Disorders

  • Includes rare conditions like fatal familial insomnia, sleep-related epilepsy, nocturnal headaches, laryngospasm, gastroesophageal reflux, and cardiac arrhythmias.

Key Terms & Definitions

  • ICSD — International Classification of Sleep Disorders, the main diagnostic manual for sleep disorders.
  • Polysomnography — The primary sleep study tool used to diagnose sleep disorders.
  • AHI (Apnea-Hypopnea Index) — Number of apneas and hypopneas per hour of sleep.
  • RDI (Respiratory Disturbance Index) — Total of apneas, hypopneas, and respiratory arousals per hour of sleep.
  • MSLT (Multiple Sleep Latency Test) — Measures daytime sleepiness and helps diagnose hypersomnolence.
  • DLMO (Dim Light Melatonin Onset) — Marker for circadian phase.
  • Cataplexy — Sudden loss of muscle tone, typical in narcolepsy type 1.
  • SOREMP (Sleep-Onset REM Period) — REM sleep within 15 minutes of sleep onset.

Action Items / Next Steps

  • Review ICSD-3 for detailed sleep disorder descriptions and criteria.
  • Read additional provided papers for deeper understanding.
  • Consider purchasing the official ICSD-3 manual for comprehensive study.

Full transcript