International Classification of Diseases (ICD) 10

The International Classification of Diseases (ICD) is published by the World Health Organization in Geneva, Switzerland. It included mental health disorders for the first time in 1948, in its sixth edition. In 1959, following widespread criticism of its classificatory scheme, the WHO commissioned a global survey of taxonomies of mental health problems, which was conducted by Stengel. The survey uncovered great disparities and substantial disagreements as to what constituted mental illness and how it should be diagnosed (diagnostic criteria and differential diagnoses).

Yet, it was not until 1968 that Stengel's recommendations were implemented in the eighth edition. The ICD-8 was descriptive and operational and did not commit itself to any theory of etiology, pathogenesis, or psychological dynamics. Still, it sported a confusing plethora of categories and allowed for rampant comorbidity (multiple diagnoses in the same patient).

The ICD10 was revolutionary. It incorporated the outcomes of numerous collaborative studies and programmes, both national and international and included input from the American Psychiatric Association, the publisher of the Diagnostic and Statistical Manual (DSM), the ICD's equivalent in North America). Consequently, the ICD and the DSM are now broadly similar.

But, as opposed to the DSM, the ICD provides two sets of diagnostic criteria for each disorder. One list is useful to the diagnostician and allows for some latitude and for the practitioner's exercise of judgment. The other set is far more precise and strict and intended to be used by scholars and researchers in their studies. Yet a third, simplified classification is applicable to primary care settings and contains only broad categories (dementia, eating disorder, psychotic disorder, and so on).

The ICD10 discusses organic, substance use-related, and stress-related disorders separately. Chapter F, which deals with mental health disorders, is divided into ten groups and each group, in turn, is again divided into one hundred subunits. Thus F2 is Schizophrenia, F25 is Schizoaffective Disorder, and F25.1 is Schizoaffective Disorder, depressive type.

An international study carried out in 112 clinical centers in 39 countries demonstrated that the ICD10 is not a reliable diagnostic tool as far as personality disorder go (Sartorius et al. 1993). These findings were not repeated a year later in the USA and Canada.