The International Classification of Sleep Disorders (ICSD) is "a primary diagnostic, epidemiological and coding resource for clinicians and researchers in the field of sleep and sleep medicine".^[1] The ICSD was produced by the American Academy of Sleep Medicine (AASM) in association with the European Sleep Research Society, the Japanese Society of Sleep Research, and the Latin American Sleep Society. The classification was developed as a revision and update of the Diagnostic Classification of Sleep and Arousal Disorders (DCSAD) that was produced by both the Association of Sleep Disorders Centers (ASDC) and the Association for the Psychophysiological Study of Sleep and was published in the journal Sleep in 1979.^[2][3] A second edition, called ICSD-2, was published by the AASM in 2005.^[4] The third edition, ICSD-3, was released by the AASM in 2014.^[5] A text revision of the third edition (ICSD-3-TR) was published in 2023 by the AASM.^[6]

In 1979, the first Diagnostic Classification of Sleep and Arousal Disorders (DCSAD) was developed by the Association of Sleep Disorders Centers (ASDC) and the Association for the Psychophysiological Study of Sleep. Disorders were divided into four main categories.^[2][3]

1. Disorders of initiating and maintaining sleep (DIMS) – Insomnias
2. Disorders of Excessive somnolence (DOES) – Hypersomnias
3. Disorders of the Sleep-Wake Schedule – Circadian Disorders
4. Dysfunctions Associated with Sleep, Sleep Stages, or Partial Arousals – Parasomnias

In 1990, the first comprehensive classification of disorders of sleep and arousal, the International Classification of Sleep Disorders (ICSD-1990), was developed by the American Academy of Sleep Medicine (AASM) in association with the European Sleep Research Society, the Japanese Society of Sleep Research, and the Latin American Sleep Society.^[7] 84 sleep disorders were inventoried, based on pathophysiological characteristics. It was later revised as the ICSD-R in 1997.

The International Classification of Sleep Disorders (ICSD) uses a multiaxial system for stating and coding diagnoses both in clinical reports or for database purposes. The axial system uses International Classification of Diseases (ICD-9-CM) coding wherever possible. Additional codes are included for procedures and physical signs of particular interest to sleep disorders clinicians and researchers. Diagnoses and procedures are listed and coded on three main "axes". The axial system is arranged as follows:^[8]

Axis A ICSD Classification of Sleep Disorders

Axis B ICD-9-CM Classification of Procedures

Axis C ICD-9-CM Classification of Diseases (nonsleep diagnoses).

1. Dyssomnias
   1. Intrinsic Sleep Disorders
   2. Extrinsic Sleep Disorders
   3. Circadian Rhythm Sleep Disorders
2. Parasomnias
   1. Arousal Disorders
   2. Sleep-Wake Transition Disorders
   3. Parasomnias Usually Associated with REM Sleep
   4. Other Parasomnias
3. Sleep Disorders Associated with Mental, Neurologic, or Other Medical Disorders
   1. Associated with Mental Disorders
   2. Associated with Neurologic Disorders
   3. Associated with Other Medical Disorders
4. Proposed Sleep Disorders
   1. Shorter Sleeper
   2. Long Sleeper
   3. Menstrual-Associated Sleep Disorders

In 2005, the International Classification of Sleep Disorders underwent minor updates and modifications resulting in version 2 (ICSD-2).^[4]

The ICSD-2 thus lists 81 sleep disorder diagnostic categories divided in 8 major categories. Each diagnostic is detailed in a description that presents the diagnostic criteria. The 81 diagnostics are divided into 8 main categories, namely insomnias, sleep-related breathing disorders, hypersomnias of central origin, circadian rhythm sleep disorders, parasomnias, sleep-related movement disorders, isolated symptoms apparently normal variants and unresolved issues, other sleep disorders. The two last categories (i.e. sleep disorders associated with disorders classified elsewhere and psychiatric disorders frequently encountered in the differential diagnosis of sleep disorders) are presented in the appendices and count 13 diagnostics.^[7]

In 2006, a pocket version of the ICSD-2 was released. In this version, a pediatric section was added listing the following diagnostic categories:

1. Behavioural Insomnia in Childhood
   1. Onset Type
   2. Limit Setting Type
2. Primary Sleep Apnea of Infancy
3. Obstructive Sleep Apnea, Pediatric
4. Congenital Central Alveolar Hypoventilation Syndrome
5. Sleep Enuresis
6. Restless Legs Syndrome
7. Sleep-related Rhythmic Movement Disorder

However, this classification brought some confusion into the field, which led to the revision of the classification in 2011. The classification was much more discussed by experts of the field and led to the third edition of the ICSD.

The revision of the ICSD-2 was firstly made by the AASM and other International Societies. This revision integrates pediatric diagnosis into clinical adult diagnosis (except for obstructive sleep apnea) and led to the third edition of the ICSD, which was released in 2014.

ICSD-3 includes 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.^[9] Furthermore, pediatric diagnoses are not distinguished from adult diagnoses except for sleep-related breathing disorders.^[10]

In addition, significant changes have been made in the nosology of insomnia, narcolepsy and parasomnia. Primary vs. secondary (i.e. comorbid) insomnia has been reunited into a single disorder: chronic insomnia. Narcolepsy has been divided into narcolepsy Type 1 and narcolepsy Type 2. These two types are distinguished by the presence or absence of cataplexy and the cerebrospinal fluid hypocretin-1 level. Concerning parasomnia, the sections have been modified, grouping together common features. Finally, a section on treatment-emerging CSA has been added to the CSA syndromes section.^[11]

It also discusses common isolated symptoms and normal variants. 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.

Furthermore, some features are no longer disorders and are reunited in the The AASM [American Academy of Sleep Medicine] Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Therefore, ICSD permanently refers to this manual. The latter allows, for instance, to find definitions of polysomnography or specific features.^[11]

The ICSD-3 counts 383 pages for 83 disorders. It is divided into 7 main categories: