3.1 Classification, Terminology, Prevalence & Acute vs. Chronic Sleep Disturbances
Key Takeaways
The ICSD-3-TR (AASM, 2023) groups sleep disorders into seven major categories: insomnia, sleep-related breathing disorders, central hypersomnolence, circadian rhythm disorders, parasomnias, sleep-related movement disorders and other sleep disorders.
Billing uses ICD-10-CM codes, such as G47.33 for obstructive sleep apnea and G25.81 for restless legs syndrome.
An estimated 936 million adults aged 30–69 worldwide have OSA (AHI ≥5), and most people with moderate-to-severe OSA remain undiagnosed.
About 30% of adults report insomnia symptoms, but about 10% meet criteria for chronic insomnia disorder; narcolepsy affects about 25–50 per 100,000 people.
Acute (short-term) disturbances last under 3 months and usually follow an identifiable trigger; chronic disorders persist at least 3 months and need structured treatment.
3.1 Classification, Terminology, Prevalence & Acute vs. Chronic Sleep Disturbances
Domain 1, Task B asks the CCSH to identify the terminology used to classify sleep disorders, recognize their clinical presentation, describe their incidence and prevalence, and differentiate acute from chronic sleep disturbances. Later chapters cover each disorder in detail; this section provides the framework.
Classification Systems
ICSD-3-TR
The International Classification of Sleep Disorders, published by the AASM, is the main clinical system for sleep medicine. The third edition (ICSD-3) appeared in 2014, and a text revision (ICSD-3-TR) in 2023. It sorts disorders into seven major categories:
| Category | Examples |
|---|---|
| Insomnia | Chronic insomnia disorder, short-term insomnia disorder |
| Sleep-related breathing disorders | Obstructive sleep apnea, central sleep apnea syndromes, sleep-related hypoventilation and hypoxemia |
| Central disorders of hypersomnolence | Narcolepsy types 1 and 2, idiopathic hypersomnia, Kleine-Levin syndrome, insufficient sleep syndrome |
| Circadian rhythm sleep-wake disorders | Delayed and advanced phase, Non-24-hour, irregular rhythm, shift work and jet lag disorders |
| Parasomnias | NREM disorders of arousal, REM sleep behavior disorder, nightmare disorder |
| Sleep-related movement disorders | Restless legs syndrome, periodic limb movement disorder, sleep-related bruxism and leg cramps |
| Other sleep disorders | Disorders that do not fit elsewhere |
The ICSD also lists isolated symptoms and normal variants (such as snoring or long and short sleepers) and medical and neurological conditions associated with sleep.
DSM-5-TR and ICD-10-CM
- The American Psychiatric Association's DSM-5-TR includes sleep-wake disorders (insomnia disorder, hypersomnolence disorder, narcolepsy, breathing-related sleep disorders, circadian rhythm disorders, parasomnias, restless legs syndrome and substance/medication-induced sleep disorder). Its criteria are similar to the ICSD's but written for mental-health settings.
- ICD-10-CM codes are used for billing in the United States. Examples include G47.33 (obstructive sleep apnea), G47.00 (insomnia, unspecified), G47.411 (narcolepsy with cataplexy), G47.52 (REM sleep behavior disorder), G47.61 (periodic limb movement disorder) and G25.81 (restless legs syndrome). The CCSH does not assign diagnoses but should recognize these codes on orders and claims.
Key Terminology
| Term | Meaning | Common confusion |
|---|---|---|
| Excessive daytime sleepiness (EDS) | Difficulty staying awake during the major wake period | Not the same as fatigue (low energy without dozing) |
| Insomnia symptom vs. insomnia disorder | A complaint of poor sleep vs. a diagnosis meeting duration, frequency and impairment criteria | Many people have symptoms without the disorder |
| Hypersomnolence | Excessive sleepiness or excessive sleep quantity | "Hypersomnia" is often used loosely for both |
| Parasomnia | Unwanted events or experiences at sleep onset, during sleep or on arousal | Not a seizure, though seizures can mimic it |
| Comorbid insomnia | Insomnia occurring with another condition | Replaces the older term "secondary insomnia" |
| Treatment-emergent central sleep apnea | Central apneas appearing on PAP | Formerly "complex sleep apnea" |
| Willis-Ekbom disease | Another name for restless legs syndrome | |
| Upper airway resistance | Respiratory effort-related arousals without apneas or hypopneas | Now classified within OSA rather than as a separate disorder |
How Common Are Sleep Disorders?
| Condition | Estimated prevalence | Notes |
|---|---|---|
| Obstructive sleep apnea | About 936 million adults aged 30–69 worldwide with AHI ≥5, including about 425 million with AHI ≥15 (2019 global estimate); in the U.S. Wisconsin cohort, moderate-to-severe OSA affected about 13% of men and 6% of women aged 30–70 | A large majority of moderate-to-severe cases are undiagnosed |
| Insufficient sleep | About one in three U.S. adults report less than 7 hours per night (CDC) | Most common sleep problem in the population |
| Insomnia | About 30% of adults report insomnia symptoms; about 10% meet criteria for chronic insomnia disorder | More common in women and older adults |
| Restless legs syndrome | 5–10% of adults in European-ancestry populations; 2–3% have moderate-to-severe symptoms needing treatment | Less common in Asian populations |
| Narcolepsy | About 25–50 per 100,000 people | Often takes years to diagnose |
| Delayed sleep-wake phase disorder | 7–16% of adolescents and young adults | Overlaps with normal adolescent phase delay |
| REM sleep behavior disorder | About 1% of older adults | Higher in Parkinson's disease |
| Pediatric OSA | About 1–5% of children | Peaks in preschool years with enlarged tonsils and adenoids |
Incidence is the number of new cases in a period; prevalence is the proportion of people who have the condition at a point in time. Prevalence rises when a disease is long-lasting even if incidence is stable, which is why chronic conditions such as OSA have high prevalence.
Acute vs. Chronic Sleep Disturbances
| Feature | Acute (short-term) | Chronic |
|---|---|---|
| Duration | Days to weeks; under 3 months for short-term insomnia disorder | 3 months or more (for insomnia, at least 3 nights per week) |
| Typical triggers | Stress, bereavement, acute illness or pain, hospitalization, travel across time zones, new medications | Ongoing disorders (OSA, RLS, narcolepsy), perpetuating behaviors, chronic medical or mental-health conditions |
| Course | Often resolves when the trigger passes | Persists or worsens without treatment |
| Management | Support, education, short-term measures, watching for persistence | Structured evaluation and treatment (for example CBT-I, PAP, iron for RLS) |
Acute insomnia can become chronic when coping behaviors such as spending extra time in bed, napping and clock-watching take hold (the 3P model). Early education during an acute episode can prevent this.
Recognizing Presentations at a Glance
Task B also asks you to recognize the clinical presentation of sleep-disordered breathing, insomnia, circadian rhythm disorders and other sleep disorders. Later chapters give details; this table shows the patterns that point toward each category.
| Main complaint | Clues in the history | Likely category | Typical next step |
|---|---|---|---|
| Snoring, witnessed pauses, unrefreshing sleep | Obesity, large neck, hypertension, morning headache, nocturia | Sleep-related breathing disorder | Screening (STOP-Bang), then PSG or HSAT as ordered |
| Trouble falling or staying asleep | Worry at bedtime, long time in bed, clock-watching, napping | Insomnia | Sleep diary, ISI, CBT-I referral |
| Can't fall asleep until very late but sleeps well on free days | Adolescent or young adult, late screen use, terrible mornings | Circadian rhythm disorder (delayed phase) | Diary and actigraphy; timed light and melatonin |
| Sleepiness despite enough sleep | Sleep attacks, cataplexy, vivid dreams at sleep onset | Central hypersomnolence | PSG followed by MSLT |
| Urge to move legs in the evening | Relief with walking, iron deficiency, pregnancy | Sleep-related movement disorder | Iron studies; clinical diagnosis |
| Unusual behaviors during sleep | Early-night sleepwalking (NREM) or late-night dream enactment (REM) | Parasomnia | Safety advice; PSG with video when ordered |
Exam Traps
- Symptom vs. disorder: a patient who "can't sleep" for three nights before a move has an insomnia symptom, not chronic insomnia disorder.
- Sleepiness vs. fatigue: sleepiness means dozing; fatigue means low energy. Depression, anemia and hypothyroidism often cause fatigue without true sleepiness.
- Incidence vs. prevalence: if 60 of 1,000 adults have RLS on a given day, the prevalence is 6%; if 12 new cases appear among the 940 who did not have it over the next year, the annual incidence is about 1.3%.
Restless legs syndrome and periodic limb movement disorder belong to which ICSD-3-TR category?
Parasomnias
Central disorders of hypersomnolence
Sleep-related movement disorders
Circadian rhythm sleep-wake disorders
Which statement about the epidemiology of obstructive sleep apnea is accurate?
OSA affects fewer than 1 in 1,000 adults in most countries studied
OSA is equally common in men and women at every age before 60
Children never develop OSA unless they have severe obesity
Most adults with moderate-to-severe OSA have not been diagnosed
A 45-year-old man has had trouble falling asleep most nights for 6 weeks since losing his job, with daytime fatigue. He slept well before. How is this best classified?
Chronic insomnia disorder, because difficulty falling asleep most nights always counts as chronic
Delayed sleep-wake phase disorder, because any trouble falling asleep indicates a delayed clock
Short-term insomnia disorder, because symptoms have lasted less than 3 months after an identifiable stressor
Not a sleep problem at all, because insomnia that follows a stressful life event never needs any attention or follow-up
Sections you finish are checked off in the contents.