What is the purpose of diagnosis?

It is important to consider the reason for making a diagnosis. For many mental disorders the reasons for making a diagnosis are quite transparent. Diagnosis can be considered to serve three main purposes:

• to ease communication by allowing a shorthand way of describing a particular sort of problem or set of clinical findings

• to allow predictions to be made about likely course

• to allow rational treatment, management and allocation of services.

Even when the primary focus of concern is not service allocation, the making of a diagnosis usually has the same significance. For example, in a forensic psychiatric setting, the diagnosis of schizophrenia says something about the condition, the likely course, and the likely response to treatment. It does not, per se, say anything about responsibility for the particular act or omission under consideration or about the cause of the illness.

This is not the case in PTSD. The diagnosis itself defines aetiology. By the nature of the aetiologically significant events, this also usually identifies a person or organisation which is allegedly responsible for causing, or failing to prevent, the disorder. The diagnosis of PTSD not only provides a useful shorthand, makes predictions about course, and suggests likely management options, but it also acts as a key.

This key can provide access to a variety of doors and resources.