The International Classification of Sleep Disorders (ICSD) is the most widely used classification system for sleep disorders. The third edition of the ICSD (ICSD-3) includes seven major categories of sleep disorders:
●Insomnia ●Sleep-related breathing disorders ●Central disorders of hypersomnolence
●Circadian rhythm sleep-wake disorders ●Parasomnias ●Sleep-related movement disorders
●Other sleep disorders
Disclosures: Brooke G Judd, MD Nothing to disclose. Michael J Sateia, MD Nothing to disclose. Susan M Harding, MD, FCCP, AGAF Nothing to disclose. April F Eichler, MD, MPH Equity Ownership/Stock Options: Johnson & Johnson [Dementia (galantamine), Epilepsy (topiramate)].
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INTRODUCTION — Diagnostic classification of sleep disorders is important because it standardizes definitions, improves awareness of the conditions, promotes a broad differential diagnosis, and facilitates a systematic diagnostic approach.
The International Classification of Sleep Disorders (ICSD) is the most widely used classification system for sleep disorders. The third edition of the ICSD (ICSD-3) includes seven major categories of sleep disorders :
●Sleep-related breathing disorders
●Central disorders of hypersomnolence
●Circadian rhythm sleep-wake disorders
●Sleep-related movement disorders
●Other sleep disorders
ICSD-3 includes 60 specific diagnoses within the seven major categories, as well as an appendix for classification of sleep disorders associated with medical and neurologic disorders. The International Classification of Diseases (ICD-9-CM and ICD-10-CM) codes corresponding to each specific diagnosis can be found within the ICSD-3 . Furthermore, pediatric diagnoses are not distinguished from adult diagnoses except for sleep-related breathing disorders . The ICSD-3 complements and refers to the regularly updated Manual for the Scoring of Sleep and Associated Events, published by the American Academy of Sleep Medicine .
The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) also classifies sleep disorders in a manner that largely parallels the ICSD-3 system .
INSOMNIA — The ICSD-3 identifies three distinct types of insomnia: short-term insomnia, chronic insomnia, and other insomnia (when the patient has insomnia symptoms but does not meet criteria for the other two types of insomnia). Previous editions had subclassified chronic insomnia into primary and comorbid types, but these were eliminated in the ICSD-3 because they did not improve diagnostic accuracy [1,2].
Chronic insomnia — The ICSD-3 consolidates all chronic insomnia diagnoses under a single disorder, chronic insomnia disorder . Chronic insomnia requires a report of a sleep initiation or sleep maintenance problem, an adequate opportunity and circumstances to sleep, and daytime consequences as the result of the insomnia symptoms. (See “Overview of insomnia”, section on ‘Types of insomnia’.)
To meet diagnostic criteria for chronic insomnia disorder, the patient should have symptoms at least three times per week over a duration of three or more months. Since insomnia is a component of many psychiatric and medical conditions, a diagnosis of chronic insomnia disorder should be considered only when the insomnia is very prominent and it requires further evaluation and treatment.
Short-term insomnia — A diagnosis of short-term insomnia must meet the same criteria as chronic insomnia except that the symptoms have been present for less than three months. The development is often temporarily related to a significant stressor. To make this diagnosis, the insomnia must be an independent focus for the patient and/or require separate clinical attention. This type of insomnia often resolves when the stressor does, or when the patient develops adequate coping mechanisms or adapts to the stressor . However, in some cases this may evolve into chronic insomnia.
SLEEP-RELATED BREATHING DISORDERS — Sleep-related breathing disorders are characterized by abnormal respiration during sleep; they occur in both adults and children . There are four major sleep-related breathing disorders:
●Central sleep apnea syndromes
●Obstructive sleep apnea (OSA) syndromes
●Sleep-related hypoventilation disorders
●Sleep-related hypoxemia disorder
These syndromes are further divided according to their etiology.
Central sleep apnea syndromes — The central sleep apnea syndromes include:
●Central sleep apnea with Cheyne-Stokes breathing (see “Central sleep apnea: Risk factors, clinical presentation, and diagnosis”)
●Central sleep apnea due a medical disorder without Cheyne-Stokes breathing (see “Central sleep apnea: Risk factors, clinical presentation, and diagnosis”)
●Central sleep apnea due to high altitude periodic breathing
●Central sleep apnea due to a medication or substance
●Primary central sleep apnea
●Primary central sleep apnea of infancy
●Primary central sleep apnea of prematurity
●Treatment-emergent central sleep apnea (see “Treatment-emergent central sleep apnea”)
Of note, treatment-emergent central sleep apnea (often referred to as complex sleep apnea in the past) was a new addition to the ICSD-3 . The criteria for this disorder include the demonstration of primarily OSA during diagnostic polysomnography. Upon initiation of treatment with positive airway pressure (PAP) without a backup rate, however, there is emergence or persistence of central apneic events despite resolution of obstructive sleep apnea. These central apneic events also cannot be attributed to another identifiable comorbidity such as Cheyne-Stokes breathing or use of a substance (eg, opioids).
Note that some patients may have central apneic events which emerge during initial PAP titration, often when transitioning from wake to sleep. These central events may resolve with implementation of and good adherence to PAP therapy (usually within one month). Verification that these central apneas have resolved can often be made with PAP machine downloads during clinical follow-up. (See “Treatment-emergent central sleep apnea”.)
Obstructive sleep apnea syndromes — The OSA syndromes include OSA in adults and OSA in children. (See “Overview of obstructive sleep apnea in adults” and “Evaluation of suspected obstructive sleep apnea in children”.)
The diagnosis of OSA in adults is made when there are 15 or more primarily obstructive respiratory events per hour, even in the absence of associated symptoms or comorbid disorders [1-3]. In adults with medical or psychiatric comorbidities (eg, hypertension, coronary artery disease, atrial fibrillation, congestive heart failure, stroke, diabetes, cognitive dysfunction, or mood disorder) or signs or symptoms including excessive sleepiness, fatigue, and/or insomnia, the diagnosis of OSA can be made when there are five or more predominantly obstructive respiratory events per hour. (See “Clinical presentation and diagnosis of obstructive sleep apnea in adults”, section on ‘Diagnosis’.)
Although in-laboratory polysomnography has long been used to evaluate for OSA, out-of-center sleep testing (OCST), also referred to as home sleep apnea testing (HSAT), is an alternative diagnostic test in selected patients. OCST procedures measure the respiratory disturbance index based on recording time. Thus, OCST may underestimate respiratory event frequency because recording time, and not sleep time, is utilized for the calculation of the index. (See “Out-of-center sleep testing for obstructive sleep apnea in adults”.)
Pediatric criteria for OSA require that at least one clinical finding (snoring, labored breathing, apnea, daytime sleepiness, hyperactivity, or other findings) is present. Polysomnographic criteria require the presence of one or more obstructive events per hour of sleep or, alternatively, evidence of obstructive hypoventilation (PaCO2 >50 mmHg for >25 percent of sleep time). In addition to obstructive events and/or obstructive hypoventilation, there must also be associated snoring, flattening of nasal airway pressure waveform, or paradoxical thoraco-abdominal movement. (See “Evaluation of suspected obstructive sleep apnea in children”, section on ‘Polysomnography’.)
Sleep-related hypoventilation disorders — The sleep-related hypoventilation disorders include:
●Obesity hypoventilation syndrome (see “Clinical manifestations and diagnosis of obesity hypoventilation syndrome”)
●Congenital central alveolar hypoventilation syndrome (see “Disorders of ventilatory control”, section on ‘Congenital central alveolar hypoventilation syndrome’)
●Late-onset central hypoventilation with hypothalamic dysfunction (see “Disorders of ventilatory control”, section on ‘Late-onset central hypoventilation syndrome’)
●Idiopathic central alveolar hypoventilation
●Sleep-related hypoventilation due to a medication or substance
●Sleep-related hypoventilation due to a medical disorder
Because hypoventilation is defined by elevated PaCO2 levels, the criteria for sleep-related hypoventilation require the presence of elevated PaCO2 levels either directly (by arterial blood gas measurement) or indirectly (by end-tidal CO2 or transcutaneous CO2 measurements). When sustained drops in arterial oxygen saturation (<88 percent for >5 minutes) occur in the absence of CO2 monitoring, the separate diagnosis of sleep-related hypoxemia disorder is utilized.
The ICSD-3 now includes diagnostic criteria for obesity hypoventilation syndrome. Criteria require daytime elevation of PaCO2 (>45 mmHg) in a patient with a body mass index (BMI) of >30 kg/m2. Demonstration of daytime hypoventilation is not required to diagnose other forms of sleep-related hypoventilation. (See “Clinical manifestations and diagnosis of obesity hypoventilation syndrome”.)
Pulmonary disorders (eg, chronic obstructive pulmonary disease, asthma) are not considered sleep-related breathing disorders themselves; however, they can cause or exacerbate abnormal breathing (eg, hypoventilation, hypoxemia) during sleep. In this context, the diagnosis of sleep-related hypoventilation or hypoxemia is made. Sleep-related laryngospasm and choking are also not considered sleep-related breathing disorders; instead, they are considered medical disorders which may arise from sleep.
CENTRAL DISORDERS OF HYPERSOMNOLENCE — The central disorders of hypersomnolence include those disorders in which the primary complaint is daytime sleepiness that is not due to another sleep disorder, including disturbed sleep or misaligned circadian rhythms . Excessive sleepiness is defined as daily episodes of an irrepressible need to sleep or daytime lapse into sleep .
The central disorders of hypersomnolence include:
●Narcolepsy type 1
●Narcolepsy type 2
●Hypersomnia due to a medical disorder
●Hypersomnia due to a medication or substance
●Hypersomnia associated with a psychiatric disorder
●Insufficient sleep syndrome
In diagnosing central disorders of hypersomnolence, careful evaluation for sleep deprivation should be carried out, especially in patients who require longer sleep periods. Sleep logs and/or actigraphy for at least a week prior to evaluation of objective sleepiness with a Multiple Sleep Latency Test (MSLT) help verify a regular sleep-wake schedule and adequate sleep time. Diagnostic criteria for narcolepsy and idiopathic hypersomnolence include MSLT criteria. (See “Approach to the patient with excessive daytime sleepiness”.)
Narcolepsy — Narcolepsy type 1 includes patients with cataplexy and/or hypocretin-1 deficiency. Narcolepsy type 1 is diagnosed by either cerebrospinal fluid hypocretin-1 deficiency (<110 pg/mL, or less than one-third of the normative values on a standardized assay); or a mean sleep latency of <8 minutes and two sleep onset rapid eye movement periods (SOREMPs; within 15 minutes of sleep onset) on an MSLT and/or the overnight polysomnogram, along with a history of clear cataplexy episodes. Note that not all patients with hypocretin-1 deficiency have cataplexy; however, they are still characterized as having narcolepsy type 1. Some will develop cataplexy later in the course of the disorder. (See “Clinical features and diagnosis of narcolepsy”.)
Narcolepsy type 2 is diagnosed with the same MSLT and SOREMP criteria as described in narcolepsy type 1; however, cataplexy and/or cerebrospinal fluid hypocretin-1 deficiency (if measured) are not present. Currently, hypocretin-1 assays are not widely available clinically.
Idiopathic hypersomnia — Idiopathic hypersomnia is diagnosed when the patient has subjective sleepiness with an MSLT showing a mean sleep latency of <8 minutes with fewer than two SOREMPs on the MSLT and the overnight polysomnogram, along with the absence of cataplexy or hypocretin-1 deficiency (if measured). It is important to rule out other causes of hypersomnolence, including sleep deprivation.
Based on the available evidence, it is unclear whether idiopathic hypersomnia is a single definable disorder, or whether it is a diverse group of disorders with different pathological mechanisms resulting in a similar clinical phenotype. (See “Idiopathic hypersomnia”.)
Kleine-Levin syndrome — Kleine-Levin syndrome and insufficient sleep syndrome are reviewed elsewhere. (See “Kleine-Levin syndrome (recurrent hypersomnia)” and “Definition and consequences of sleep deprivation”.)
Other hypersomnias — In hypersomnia due to a medical or a psychiatric disorder, as well as hypersomnia due to medication or substance, the diagnosis can be made without performing an MSLT. Clinical judgment is important in diagnosing all central disorders of hypersomnolence. Furthermore, other sleep disorders (eg, obstructive sleep apnea or circadian rhythm sleep-wake disorders) can give rise to excessive sleep time and hypersomnolence and must be properly diagnosed and treated before the diagnosis of a central disorder of hypersomnolence is made.
CIRCADIAN RHYTHM SLEEP-WAKE DISORDERS — Circadian rhythm sleep-wake disorders are characterized by a chronic or recurrent sleep disturbance due to alteration of the circadian system or misalignment between the environment and an individual’s sleep-wake cycle . There are several types of circadian rhythm disorders:
●Shift work disorder and jet lag disorder are the most common types of circadian rhythm sleep disturbances, although these do not often come to medical attention. (See “Jet lag” and “Performance and safety risks of sleep deprivation and sleep disorders”, section on ‘Circadian rhythm sleep-wake disorders’.)
●Delayed sleep-wake phase disorder is characterized by sleep and wake times that are habitually delayed compared with conventional times. Sleep is usually normal once it is initiated. A typical patient has difficulty falling asleep and awakens late. This disorder is more prevalent in younger patients.
●Advanced sleep-wake phase disorder is characterized by sleep and wake times that are habitually early compared with conventional times. A typical patient falls asleep early and awakens early spontaneously. This disorder is not commonly reported, but it is more likely to be observed in older adults.
●Irregular sleep-wake rhythm disorder is characterized by lack of a clearly defined circadian rhythm of sleep and wake. This disorder is commonly associated with developmental disorders in children and in adults with neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and Huntington disease.
●Non-24-hour sleep-wake rhythm disorder is characterized by fluctuating periods of insomnia and/or excessive sleepiness that occur because the intrinsic circadian pacemaker is not entrained to a 24-hour light/dark cycle. Most individuals with this disorder are totally blind, and the failure to entrain circadian rhythms is related to the lack of photic input to the circadian pacemaker.
●Circadian sleep-wake disorder not otherwise characterized.
●Circadian rhythm disorders can also be due to a medical, psychiatric, or neurologic disorder.
General criteria common to all of the circadian rhythm sleep-wake disorders include:
●A chronic or recurrent pattern of sleep-wake rhythm disruption caused by an alteration in the endogenous circadian timing system and the desired or required sleep-wake schedule
●The presence of a sleep-wake disturbance, including insomnia and/or excessive sleepiness
●Associated distress or impairment
All disorders, except jet lag disorder, require a symptom duration of at least three months. Optimally, circadian timing is documented objectively with actigraphy and/or biomarkers such as dim-light melatonin onset. Validated questionnaires, including the morningness-eveningness questionnaire to identify chronotype, can also be helpful but are not required to make the diagnosis of circadian rhythm sleep-wake disorders.
PARASOMNIAS — Parasomnias are undesirable physical events (movements, behaviors) or experiences (emotions, perceptions, dreams) that occur during entry into sleep, within sleep, or during arousals from sleep . The observed behaviors are more complex and appear more purposeful than the stereotyped activity seen in movement disorders.
The parasomnia category is divided into non-rapid eye movement (NREM)-related parasomnias, rapid eye movement (REM)-related parasomnias, and other parasomnias.
NREM-related parasomnias — NREM-related parasomnias are disorders of arousal. They include confusional arousals, sleepwalking, sleep terrors, and sleep-related eating disorder. (See “Sleepwalking and other parasomnias in children”.)
The general criteria for the NREM-related parasomnias include:
●Recurrent episodes of incomplete awakening
●Absent or inappropriate responsiveness
●Limited or no cognition or dream report, and
●Partial or complete amnesia for the event
Each disorder has further diagnostic criteria; however, patients may meet diagnostic criteria for more than one condition. As an example, an individual can meet criteria for both sleep terrors and sleepwalking.
REM-related parasomnias — REM-related parasomnias involve the intrusion of the features of REM sleep into wakefulness (eg, sleep paralysis), exaggeration of the features of REM sleep (eg, nightmare disorder), or failure to manifest one of the core features of REM sleep (eg, lack of atonia as observed in REM sleep behavior disorder).
Diagnosis of REM sleep behavior disorder (RBD) requires the presence of repeated episodes of behavior or vocalization during REM sleep. In addition, there must be evidence of REM sleep without atonia during polysomnography. Clinical findings of RBD may also be noted in patients taking certain medications (such as selective serotonin or serotonin-norepinephrine reuptake inhibitors). In these patients, the diagnosis of RBD is still made (and not parasomnia due to medication or substance) if the diagnostic criteria for RBD are met. (See “Rapid eye movement sleep behavior disorder”.)
Nightmare disorder is characterized by recurrent, highly dysphoric/anxiety-laden dreams which are clearly recalled upon awakening and which result in significant distress and/or impairment. Nightmares are a common element of other disorders, especially post-traumatic stress disorder. This diagnosis is made only when the nightmares become a focus of clinical attention and/or require independent treatment.
Other parasomnias — Other parasomnias bear no specific relationship to sleep stage. These include: exploding head syndrome, sleep-related hallucinations, sleep enuresis, parasomnia associated with medical disorders, parasomnia due to a medication or substance, and unspecified parasomnia.
SLEEP-RELATED MOVEMENT DISORDERS — Sleep-related movement disorders are characterized by simple, stereotypic movements that disturb sleep . Patients may or may not be aware of these movements.
Symptoms of sleep disturbance (eg, daytime sleepiness, fatigue) are required to diagnose a sleep-related movement disorder. Movements that occur during sleep but do not adversely affect sleep or daytime function are not considered a sleep-related movement disorder. Restless legs syndrome/Willis-Ekbom disease (RLS/WED) is also included in this group of disorders; however, dysesthesias during wakefulness are the primary symptom.
Sleep-related movement disorders include:
●Restless legs syndrome/Willis-Ekbom disease
●Periodic limb movement disorder
●Sleep-related bruxism (teeth grinding)
●Sleep-related rhythmic movement disorder
●Benign sleep myoclonus of infancy
●Propriospinal myoclonus at sleep onset
●Sleep-related movement disorder due to a medical disorder
●Sleep-related movement disorder due to a medication or substance
●Sleep-related movement disorder, unspecified
Restless legs syndrome/Willis-Ekbom disease — RLS/WED is categorized as a sleep-related movement disorder due to its close association with periodic limb movements and its temporal relationship to sleep onset, even though it does not primarily manifest as simple, stereotypic movements. (See “Clinical features and diagnosis of restless legs syndrome/Willis-Ekbom disease in adults” and “Restless legs syndrome/Willis-Ekbom disease and periodic limb movement disorder in children”.)
The ICSD-3 diagnostic criteria for RLS/WED include the urge to move the legs and/or the presence of uncomfortable sensations that occur primarily with rest/inactivity, are at least partially relieved with movement (as long as the movement persists), and have a circadian aspect in that the symptoms occur primarily in the evening or night . Also, the ICSD-3 criteria require that an associated sleep disorder, distress, or impairment is present. (See “Clinical features and diagnosis of restless legs syndrome/Willis-Ekbom disease in adults”.)
Periodic limb movement disorder — Periodic limb movements are frequently noted during polysomnography. For periodic limb movements to be considered a disorder, they must occur on polysomnography more than 15 times per hour in adults or more than 5 times per hour in children. In addition, an individual must report a sleep disturbance or some form of functional impairment that is causally related to the periodic limb movements.
Periodic limb movement disorder should not be diagnosed with concurrent untreated obstructive sleep apnea, RLS/WED, narcolepsy, or REM sleep behavior disorder (RBD), since periodic limb movements are commonly seen with these disorders.
OTHER SLEEP DISORDERS — This category includes sleep disorders that cannot be appropriately classified elsewhere in the third edition of the International Classification of Sleep Disorders (ICSD-3), either because the disorder overlaps with more than one category or when insufficient data has been collected to firmly establish another diagnosis . Disorders that are exclusively related to environmental disturbance may also be classified here.
ISOLATED SYMPTOMS AND NORMAL VARIANTS — Other sleep-related symptoms or events do not meet the standard definition of a sleep disorder .
●Some occur during normal sleep. As an example, sleep talking occurs at some time in most normal sleepers.
●Some lie on the continuum between normal and abnormal. As an example, snoring without associated airway compromise, sleep disturbance, or other consequences is essentially normal, whereas heavy snoring is often part of obstructive sleep apnea. (See “Overview of snoring in adults”.)
APPENDICES — The third edition of the International Classification of Sleep Disorders (ICSD-3) includes two appendices :
●Appendix A includes diagnoses that can be classified as medical or neurologic disorders (eg, fatal familial insomnia, sleep-related epilepsy or headaches, sleep-related laryngospasm, sleep-related gastroesophageal reflux, and sleep-related myocardial ischemia). (See “Diseases of the central nervous system caused by prions”, section on ‘Fatal familial insomnia’.)
●Appendix B is a guide to the International Classification of Diseases (ICD-10-CM) coding for substance-induced sleep disorders.
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, “The Basics” and “Beyond the Basics.” The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on “patient info” and the keyword(s) of interest.)
●Beyond the Basics topics:
●The third edition of the International Classification of Sleep Disorders (ICSD-3) classifies sleep disorders into seven major categories: insomnia, sleep-related breathing disorders, central disorders of hypersomnia, circadian rhythm sleep-wake disorders, parasomnias, sleep-related movement disorders, and other sleep disorders. (See ‘Introduction’ above.)
●The ICSD-3 identifies three distinct types of insomnia: short-term insomnia, chronic insomnia, and other insomnia (when the patient has insomnia symptoms but does not meet criteria for the other two types of insomnia). (See ‘Insomnia’ above.)
●Sleep-related breathing disorders are characterized by abnormal respiration during sleep; they occur in both adults and children. There are four major sleep-related breathing disorders: central sleep apnea syndromes, obstructive sleep apnea syndromes, sleep-related hypoventilation disorders, and sleep-related hypoxemia disorder. (See ‘Sleep-related breathing disorders’ above.)
●The central disorders of hypersomnolence include those disorders in which the primary complaint is daytime sleepiness that is not due to another sleep disorder, including disturbed sleep or misaligned circadian rhythms. (See ‘Central disorders of hypersomnolence’ above.)
●Circadian rhythm sleep-wake disorders are characterized by a chronic or recurrent sleep disturbance due to alteration of the circadian system or misalignment between the environment and an individual’s sleep-wake cycle. (See ‘Circadian rhythm sleep-wake disorders’ above.)
●Parasomnias are undesirable physical events (movements, behaviors) or experiences (emotions, perceptions, dreams) that occur during entry into sleep, within sleep, or during arousals from sleep. (See ‘Parasomnias’ above.)
●Sleep-related movement disorders are characterized by simple, stereotypic movements that disturb sleep. Restless legs syndrome/Willis-Ekbom disease is the most common sleep-related movement disorder, although dysesthesias during wakefulness are the primary symptom. (See ‘Sleep-related movement disorders’ above.)
- International Classification of Sleep Disorders, 3rd ed, American Academy of Sleep Medicine, Darien, IL 2014.
- Sateia MJ. International classification of sleep disorders-third edition: highlights and modifications. Chest 2014; 146:1387.
- Berry RB, Brooks R, Gamaldo CE, et al. AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, 2.0.2, American Academy of Sleep Medicine, Darien, Illinois 2013.
- American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), American Psychiatric Association, Arlington, VA 2013.