CHAPTER 3 Classification
The classification of psychiatric disorders has been subject to changes over the decades. The two most well accepted and widely used current systems are the World Health Organization’s International Classification of Diseases, tenth edition (ICD–10), and the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, fourth edition, revised (DSM–IVTR). These two classification systems differ in a number of important ways (see Table 3.1), but in terms of the psychiatric disorders they describe, there is rather more congruence than dissonance.
TABLE 3.1 Differences between DSM–IVTR and ICD–10
| DSM–IVTR | ICD–10 |
|---|---|
| US-based, published by the American Psychiatric Association, but has wide acceptance around the globe | Published by the World Health Organization; international perspective, and encompasses a diversity of opinion, including from a developing country perspective |
| Not part of a general medical classification system | Part of a general medical classification system |
| One version only | Clinical and research versions |
| Atheoretical | Groupings (‘blocks’) on the basis of presumed shared aetiologies |
| Multiaxial, with personality disorders on a separate axis (Axis II) | Personality disorders and intellectual disability (mental retardation) not on a separate axis |
| Global functioning assessed using the Global Assessment of Functioning (GAF) Scale | Disability assessed using the Disability Assessment Schedule (WHO–DAS) |
One feature of both systems is that they provide operational criteria that rule diagnosis (ICD–10 applies operational criteria only in its research version). Operational criteria essentially provide a checklist of symptoms and signs, a proportion of which need to be endorsed for the subject to be considered a ‘case’; there are also usually some exclusionary items, such as a clear organic cause for the signs and symptoms. This approach has the downside of to some extent eschewing clinical intuition and judgment, and can lull one into a false sense of security regarding the validity of the constructs they describe. Indeed, none of the disorders in the nosologies are necessarily ‘true’ entities, and the boundaries of many are permeable. Also, there is a danger of labelling individuals according to their diagnosis, with all the associated downsides. Arguably, the psychiatric formulation is a much more satisfactory approach to understanding the individual and why they are presenting with certain symptoms at a specific time (see Ch 1).
The pragmatic classification system
Figure 3.1 provides a schematic representation of the major psychiatric disorders in adults. A number of general issues should be noted:
It should also be noted that this schematic applies to adult psychopathology, and child and adolescent psychiatry adopts a somewhat different approach (see Ch 16). Finally, the schematic does not explicitly include the addictive disorders (see Ch 20), though they can be subsumed under the ‘organic’ rubric.
Organic disorders
In clinical practice, it is vital to examine each patient physically, and to perform laboratory tests where indicated (see Ch 2). One can consider organic factors as:
Causal. The factor is sufficient to cause the psychiatric symptoms (e.g. a temporal lobe tumour presenting as a post-ictal psychosis).
