Classification of mental disorders

# Overview
The classification of mental disorders is a key aspect of psychiatry and other mental health professions and an important issue for users and providers of mental health services. There are currently two widely established systems for classifying mental illness - Chapter V of the International Classification of Diseases (ICD-10) produced by the World Health Organization (WHO) and the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) produced by the American Psychiatric Association (APA). Both list categories of disorders thought to be distinct types, and have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes may be in use more locally, for example the Chinese Classification of Mental Disorders. Other manuals are used by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual. Generally there is a significant scientific debate about the relative merits of a categorical system or a dimensional system (also known as a continuum or spectrum system), as well as significant controversy about the role of science and values in classification schemes and the professional, legal and social uses to which they are put.

# Historical Development
In Ancient Greece, Hippocrates and his followers are generally credited with the first classification system for mental llnesses, including mania, melancholia, and paranoia. They held that dysfunction in the brain as well as the rest of the body was due to imbalances in the four humors. Evolution in the scientific concepts of psychopathology (literally referring to diseases of the mind) took hold in the late 18th and 19th centuries following the Renaissance and Enlightenment. Individuals behaviors that had long been recognized came to be grouped into syndromes, notably by Pinel and then Kraepelin. Early 20th Century schemes in Europe and the United States reflected a brain disease model that had emerged during the 19th Century, as well as some ideas from Darwin's theory of evolution and/or Freud's psychoanalytic theories. Meyer advanced a mixed biosocial scheme that  emphasized the reactions and adaptations of the whole organism to life experiences. Jellife and White created a scheme including neuroses like "shellshock" and disorders such as "dementia praecox" and manic-depressive psychoses. In 1945, Menninger advanced a classification scheme synthesizing ideas of the time into five major groups. This system was adopted by the Veterans Administration in the United States and strongly influenced the DSM. The DSM and ICD developed, partly in synch, in the context of mainstream psychiatric research and theory. Debates continued and developed about the definition of mental illness, the medical model, categorical vs dimensional approaches, and whether and how to include suffering and impairment criteria.

# Definitions
In the scientific and academic literature on the definition of mental disorder, one extreme argues that it is entirely a matter of value judgements (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms); other views argue that the concept refers to a "fuzzy prototype" that can never be precisely defined, or that the definition will always involve a mixture of scientific facts (e.g. that a natural or evolved function isn't working properly) and value judgements (e.g. that it is harmful or undesired). Lay concepts of mental disorder vary considerably across different cultures and countries, and may refer to different sorts of individual and social problems.
The World Health Organization (WHO) and national surveys report that there is no single consensus on the definition of mental disorder/illness, and that the phrasing used depends on the social, cultural, economic and legal context in different contexts and in different societies. The WHO reports that there is intense debate about which conditions should be included under the concept of mental disorder; a broad definition can cover mental illness, mental retardation, personality disorder and substance dependence, but inclusion varies by country and is reported to be a complex and debated issue. There may be a criterion that a condition should not be expected to occur as part of a person's usual culture or religion.
Most international clinical documents avoid the term "mental illness", preferring the term "mental disorder" However, some use "mental illness" as the main over-arching term to encompass mental disorders. Some consumer/survivor movement organizations oppose use of the term mental illness on the grounds that it supports the dominance of a medical model. The term "serious mental illness" (SMI) is sometimes used to refer to more severe and long-lasting disorder while "mental health problems" may be used as a broader term, or to refer only to milder or more transient issues. Confusion often surrounds the ways and contexts in which these terms are used.

# ICD-10
The International Classification of Diseases (ICD) is an international standard diagnostic classification for a wide variety of health conditions. Chapter V focuses on "mental and behavioural disorders" and consists of 10 main groups:
- F0 Organic, including symptomatic, mental disorders
- F1 Mental and behavioural disorders due to use of psychoactive substances
- F2 Schizophrenia, schizotypal and delusional disorders
- F3 Mood  disorders
- F4 Neurotic, stress-related and somatoform disorders
- F5 Behavioural syndromes associated with physiological disturbances and physical factors
- F6 Disorders of personality and behaviour in adult persons
- F7 Mental retardation
- F8 Disorders of psychological development
- F9 Behavioural and emotional disorders with onset usually occurring in childhood and adolescence
- In addition, a group of unspecified mental disorders.
Within each group there are more specific subcategories. The ICD includes personality disorders on the same domain as other mental disorders, unlike the DSM. The ICD-10 states that mental disorder is "not an exact term", although is generally used "...to imply the existence of a clinically recognisable set of symptoms or behaviours associated in most cases with distress and with interference with personal functions." (WHO, 1992).
The WHO is revising their classifications in this section as part of the development of the ICD-11 (scheduled for 2014) and an "International Advisory Group" has been established to guide this.

# DSM-IV
The DSM-IV, produced by the American Psychiatric Association, characterizes mental disorder as "a clinically significant behavioral or psychological syndrome or pattern that occurs in an individual,...is associated with present distress...or disability...or with a significant increased risk of suffering." but that "...no definition adequately specifies precise boundaries for the concept of "mental disorder"...different situations call for different definitions" (APA, 1994 and 2000). The DSM also states that "there is no assumption that each category of mental disorder is a completely discrete entity with absolute boundaries dividing it from other mental disorders or from no mental disorder."
The DSM-IV-TR (Text Revision, 2000) consists of five axes (domains) on which disorder can be assessed. The five axes are:
Axis I
Clinical Disorders (all mental disorders except Personality Disorders and Mental Retardation)
Axis II
Personality Disorders and Mental Retardation
Axis III
General Medical Conditions (must be connected to a Mental Disorder)
Axis IV
Psychosocial and Environmental Problems (for example limited social support network)
Axis V
Global Assessment of Functioning (Psychological, social and job-related functions are evaluated on a continuum between mental health and extreme mental disorder)
The main categories of disorder in the DSM are:

# Other schemes
The Chinese Society of Psychiatry's Chinese Classification of Mental Disorders (currently CCMD-3)
The Latin American Guide for Psychiatric Diagnosis (GLDP)..

# Childhood Diagnosis
The Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood (DC:0-3) was first published in 1994 by Zero to Three to classify mental health and developmental disorders in the first four years of life. It is sometimes used as a complement to the DSM and ICD, and has been published in 9 languages.
The Research Diagnostic criteria-Preschool Age (RDC-PA) was developed in 2000 to 20002 by a task force of independent investigators with the goal of developing clearly specified diagnostic criteria to faciliate research on psychopathology in this age group.

# Usage
The ICD and DSM classification schemes have achieved much widespread acceptance in psychiatry. A survey of 205 psychiatrists, from 66 different countries across all continents, found that ICD-10 was more frequently used and more valued in clincal practice and training, while the DSM-IV was more valued for research, with accessibility to either being limited, and usage by other mental health professionals, policy makers, patients and families less clear. A primary care (e.g. general or family physician) version of the mental disorder section of ICD-10 has been developed (ICD-10-PHC) which has also been used quite extensively internationally
In Japan, most university hospitals use either the ICD or DSM. ICD appears to be the somewhat more used for research or academic purposes, while both were used equally for clinical purposes. Other traditional psychiatric schemes may also be used.

# Categorical classification
The classification schemes in common usage are based on separate (but may be overlapping) categories of disorder cheme sometimes termed "neo-Kraepelinian" (after the psychiatrist Kraepelin) which is intended to be atheoretical with regard to etiology (causation). These classification schemes have achieved some widespread acceptance in psychiatry and other fields, and have generally been found to have improved inter-rater reliability, although routine clinical usage is less clear. Questions of validity and utility have been raised, both scientifically and in terms of social, economic and political factors - notably over the inclusion of certain controversial categories, the influence of the pharmaceutical industry, or the stigmatizing effect of being categorized or labelled.

# Non-Categorical schemes
Other classification schemes are not based on categories with cut-offs separating the ill from the healthy or the abnormal from the normal (sometimes termed "threshold psychiatry"). Classification may instead be based on broader underlying "spectra", where a spectrum may link together a range of other categorical diagnoses and nonthreshold symptomology in the general population Or a scheme may be based on a set of continuously-varying dimensions, with each individual having a different profile of low or high scores across the different dimensions. Another approach may be based directly on the specific complaints reported by an individual. DSM-V planning committees are currently establishing the research base to move towards a dimensional classification of some disorders, including personality disorder The Psychodynamic Diagnostic Manual has an emphasis on dimensionality and the context of mental problems.

# Cultural differences
Classification schemes may not apply to all cultures. The DSM is based on predominantly American research studies and has been said to have a decidedly American outlook, meaning that differing disorders or concepts of illness from other cultures (including personalistic rather than naturalistic explanations) may be neglected or misrepresented, while Western cultural phenomena may be taken as universal. Culture-bound syndromes are those hypothesized to be specific to certain cultures (typically taken to mean non-Western or non-mainstream cultures); while some are listed in an appendix of the DSM-IV they are not detailed and there remain open questions about the relationship between Western and Non-Western diagnostic categories and sociocultural factors, which are addressed from different directions by, for example, Cross-cultural psychiatry or anthropology.