Range and Classification of Sleep Disorders
2.2 The Evolution of Sleep Disorder Classifications
During the 1970s sleep disorders began to appear in disease classification sys- tems (Edinger and Morin 2012) (Table 2.1). The first inclusion of sleep disorders was in 1977 in the International Classification of Diseases (ICD) published by the WHO.
2.2.1 The International Classification of Diseases (ICD)
The WHO oversees the International Classification of Diseases (ICD) revisions and the allocation of numeric and alphanumeric codes to designate disease diagnoses and health problems for electronic storage, retrieval and analysis of data (World Health Organization 1977, 1994, 2011). ICD codes are given to every diagnosis, description of symptoms and cause of death attributable to human beings. This is the international standard for defining and reporting diseases and health conditions.
The most current version of the ICD in use is the 10th revision, the ICD-103. The ICD-10 was developed from 1983 and completed in 1992 and is used by more than 100 countries around the world. The 2010 edition of ICD-10 includes updates that came into effect between 1998 and 2010 and is also referred to as the 4th edition of ICD-10. Work on the 11th revision of the classification is underway and due for release in 2018. National versions of the ICD, for example, in the USA called Clinical Modifications ICD-10-CM, frequently include much more detail and some- times have separate sections for procedures. Given the extensive use of the ICD codes in healthcare and for statistical analysis in the era of electronic health records, it is vital that these codes be included in the classification of sleep disorders.
In early versions of the ICD, some sleep disorders such as narcolepsy, restless legs syndrome (RLS) and sleep-related breathing disorders had already been listed under clinical sections, and they have remained under these original categories in more recent revisions. The ICD-9-CM2 included sleep disorders under two major subheadings, namely, “Specific Disorders of Sleep of Nonorganic Origin” (ICD code #307.4) and
“Sleep Disturbances” (ICD code# 780.5). The nonorganic disorders included those con- sequent to phase-shifting of the sleep-wake cycle, for example, shift work (307.45-1) or jet lag (307.45-0), as well as types based on the chronicity of the complaint as transient or persistent, for example, inadequate sleep hygiene (307.41-1) and persistent disorder of initiating or maintaining sleep (307.42). Also included in the nonorganic subtype were some parasomnias such as nightmares (307.47-0) and sleep talking (307.47-3), whereas other parasomnias such as sleep paralysis (780.56-2) and REM sleep behaviour disorder (780.59-0) were categorized under the (organic) category of sleep disturbances.
2.2.1.1 Sleep Disturbance/Disorder Categorization Based on Aetiology
A major consideration in the ICD-9 diagnostic categorization of sleep disorders was the distinction of whether the aetiology was “organic” (i.e. “true” or endogenous sleep disturbances) or “nonorganic” (i.e. due largely to external factors), which in practice is often a challenge to distinguish with sleep disorders (Edinger and Morin 2012). Recognizing that sleep problems may evolve from a combination of endog- enous and exogenous factors, the initial classification system of the Association of Sleep Disorders Centres in 1979 for sleep specialists made no attempt to utilize the scheme of organic versus nonorganic (Association of Sleep Disorders Centers 1979). The subsequent classification system for sleep specialists (ICSD) (American Sleep Disorders Association 1990, 1997) opted to use the subdivisions of “intrinsic”
(coming from within the body) or “extrinsic” (produced primarily by factors outside the body), but this was eliminated in the second and third edition of ICSD. The early
editions of the APA’s classification also included a diagnostic distinction of sleep disorders based on aetiology, but in this case as “primary” or “secondary” (American Psychiatric Association 1994), while in the current DSM-5, this distinction no lon- ger applies (American Psychiatric Association 2013).
2.2.2 The Diagnostic and Statistical Manual of Mental Disorders (DSM)
The 1970s also brought in a refinement of diagnostic criteria for mental disorders as incorporated in the 8th revision of the ICD. Building on this work, starting with the 3rd revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM) published in 1980 by the APA, there was an effort to align their nomenclature to be more consistent with that of the ICD. Published in 1987, the DSM-III-R was the first time sleep disorders appeared in the DSM (Edinger and Morin 2012). However, with regard to sleep disorders, these two classification systems, ICD and DSM, presented two different nosological frameworks (see Table 2.1).
In the DSM-IV published in 1994, sleep disorders were organized into four major sections according to presumed aetiology (American Psychiatric Association 1994).
1. Primary sleep disorders are those in which none of the aetiologies listed below (i.e. another mental disorder, a general medical condition or a substance) is responsible.
2. Sleep disorder related to another mental disorder.
3. Sleep disorder related to a general medical condition.
4. Sleep disorder induced by a substance.
These latter three groups form separate sleep disorder categories. Under the cat- egory of “sleep disorder related to another mental disorder”, the two subtypes were based on the essential feature of either insomnia (307.42) or hypersomnia (307.44).
When a disturbance to sleep was severe enough to warrant independent clinical attention and was due to a general medical condition, it would be classified under
“sleep disorder related to a general medical condition” (780.xx) with four subtypes of insomnia, hypersomnia, parasomnia or mixed. These four subtypes were also used under the category of “sleep disorder induced by a substance” along with the appli- cable substance type, for example, alcohol, amphetamine or sedative hypnotic.
The “primary sleep disorders” were subdivided into dyssomnias (characterized by abnormalities in the amount, quality or timing of sleep) and parasomnias (char- acterized by abnormal behavioural or physiological events occurring in association with sleep, specific sleep stages or sleep-wake transitions). Dyssomnias included primary insomnia (307.42), primary hypersomnia (307.44), narcolepsy (347) and breathing-related sleep disorder (780.59) leading to excessive sleepiness or insom- nia. Dyssomnias also included circadian rhythm disorder (307.45) which included delayed sleep phase (780.55-0), jet lag (307.45-0), shift work (307.45-1) or unspeci- fied type. Finally, dyssomnia not otherwise specified (307.47) included those due to
environmental factors, or attributable to sleep deprivation, RLS or periodic limb movements (PLMS) also known as nocturnal myoclonus. The subcategory of para- somnias included nightmare disorder (307.47) formerly known as dream anxiety disorder, sleep terror disorder (307.46), sleepwalking disorder (307.46) and para- somnia not otherwise specified (307.47), for example, REM sleep behaviour disor- der (RBD) and sleep paralysis.
It is important to recognize that the DSM was prepared for use by mental health and general clinicians, not experts in sleep medicine, and therefore represented an effort to simplify sleep-wake disorder classification by aggregating diagnoses under broad labels. In contrast to this clustering approach, the classification system for sleep specialists includes a large number of highly specific sleep disorder diagnoses.
2.2.3 Diagnostic Classification of Sleep and Arousal Disorders Adding to the mix, in 1979 a third nosological framework entirely different than those of the ICD and DSM was presented by professional sleep societies—the Association of Sleep Disorders Centres (ASDC) and the Association for the Psychophysiological Study of Sleep—and published in the journal Sleep (Association of Sleep Disorders Centers 1979). Unique to this nosology, prepared by researchers and clinicians specializing in sleep, was the inclusion of the term
“arousal” in a manual entitled the Diagnostic Classification of Sleep and Arousal Disorders. This classification system was based on four categories grouped into disorders of initiating and maintaining sleep (DIMS), disorders of excessive day- time sleepiness (DOES), sleep-wake schedule disorders and parasomnias.
2.2.4 The International Classification of Sleep Disorders (ICSD) Introduced in 1990 and revised in 1997, the International Classification of Sleep Disorders (ICSD) manual was produced by the American Academy of Sleep Medicine (AASM) in collaboration with the European Sleep Research Society (ESRS), the Japanese Society of Sleep Research and the Latin American Sleep Society (American Sleep Disorders Association 1990, 1997). The ICSD was devel- oped as a revision and update of the 1979 Diagnostic Classification of Sleep and Arousal Disorders. In general, it was agreed that the first two categories, namely, the disorders of initiating and maintaining sleep (DIMS) and the disorders of excessive somnolence (DOES), were very helpful in considering the differential diagnosis of patients presenting with one or both of those major sleep symptoms. However, com- plaints of insomnia or excessive sleepiness could also be the result of disorders listed within the other two sections—disorders of the sleep-wake schedule (DSWS) and the parasomnias. Furthermore, some diagnostic entries were listed in more than one section. This updated classification system was based on a pathophysiological and symptom-based organization to facilitate a multidisciplinary approach.
Comprised of four categories, the ICSD listed 88 sleep disorders. As with the DSM-IV, in the ICSD the primary sleep disorders were classified under two
groups—dyssomnias and parasomnias. The remaining two categories were sleep disorders associated with mental, neurological or other medical disorders and pro- posed sleep disorders.
Published in 2005, the 2nd edition of the ICSD (ICSD-2) (American Academy of Sleep Medicine 2005) reflected the science and opinions of the sleep specialist com- munity and was prepared for use by specialists in sleep medicine. The ICSD-2 included 81 highly specific sleep disorders and 8 major categories as summarized in Table 2.1.
The eight categories were insomnia, sleep-related breathing disorders, hypersomnias of central origin, circadian rhythm sleep disorders, the parasomnias, sleep-related movement disorders, isolated symptoms that are apparently normal variants and unre- solved issues and other sleep disorders. Interestingly, the second edition was a return to a classification system based on phenomenology resembling the 1979 system.