The definition of a mental disorder is important for investigation as well as for health care and the insurance industry (especially health insurance and pension insurance).

The following elements are of particular importance for the definition of a mental disorder:

• Personal harm and suffering
• Abnormality (statistical, social, individual)
• Limitations or disabilities in what a person can perform
• Danger for others or the individual him/herself

In most instances more than one of these elements have to occur at the same time.

In order to standardize the description and interpretation of mental disorders, diagnosis and classification systems have been set up.

At present there exist two established classification systems for mental disorders: The International Classification of Diseases (ICD-10) published by the World Health Organization (WHO) and the classification system of the American Psychiatric Association (APA), the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV).

Both classification systems converged strongly in their last revisions, therefore diagnoses are comparable for the most relevant points.

ICD-10

The International Classification of Diseases (ICD) is an international standard diagnostic classification for all general epidemiological and many health management purposes, published by WHO. It now exist in its tenth revision. Chapter V is relevant for mental and behavioural disorders.

The ICD-10-classification for mental disorders 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 [affective] 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, there is a group of “unspecified mental disorders”.

For the chapter of mental disorders, every main group has the identification letter “F”. For each group exist more specific subcategories.

For more information see the ICD webpage of the WHO: http://www.who.int/classifications/icd/en/

DSM-IV

The classification system of the American Psychiatric Association (APA), the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), consists of five axes of disorders. Thereby it is suggested to the diagnostician not to focus only on one clinical disorder, but as well to consider other important aspects.

The five axes of DSM-IV are:

Axis I
Clinical Disorders (all mental disorders except Personality Disorders and Mental Retardation)

Axis II
Personality Disorders and Mental Retardation

Axis III
Somatic (Non-Mental) Medical Conditions

Axis IV
Psychosocial and Environmental Problems (for example problems with primary support group)

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 clinical disorders (Axis I) according to DSM-IV are:

1. Disorders Usually First Diagnosed in Infancy, Childhood, or Adolescence
2. Delirium, Dementia, and Amnestic and Other Cognitive Disorders
3. Mental Disorders Due to a General Medical Condition Not Elsewhere Classified
4. Subtance-related Disorders
5. Schizophrenia and Other Psychotic Disorders
6. Mood Disorders
7. Anxiety Disorders
8. Somatoform Disorders (Disorders with somatic symptoms)
9. Facticious Disorders (Disorders involving faking)
10. Dissociative Disorders (for example multiple-personalities)
11. Sexual and Gender Identity Disorders
12. Eating Disorders
13. Sleep Disorders
14. Impulse Control Disorders Not Elsewhere Classified
15. Adjustment Disorders
16. Other Conditions That May Be a Focus of Clinical Attention