What is a diagnosis and why is it important?

During our lifetime most of us will have had the experience of having had a physical illness or a form of medical condition for which we have seen a doctor and been treated. We would all realise then that there is a process the doctor uses for defining what that illness or condition is so that the most appropriate treatment can be applied. In most cases where there is some doubt about the condition or illness your doctor will recommend and arrange for a number of tests, including pathology, scans, X-rays and exploratory investigations to confirm the specific illness or condition.In mental illnesses and disorders it is no different a process. Except that, clearly, some of the more intrusive investigations and tests requiring pathology and microbiology may not be appropriate to use, in diagnosing the condition.In both cases, the physical and the mental, while there is a significant investment in clinical expertise and skills generally, the art of diagnosis is not an exact science. In many instances the recency or timing of the condition and a lot of external factors could mask the emerging symptoms and signs of the illness or condition.Because of these factors it can be difficult for the treating doctor to satisfy the need of their patient in defining what condition or illness they may suffer from. In fact the defining diagnosis could change over the course of time from, say, acute gastritis to amoebic dysentery, or from chronic depression to bipolar disorder.In determining mental illnesses or disorders clinicians, including general practitioners, nurses, psychiatrists, psychologists and other allied health staff, have access to two significant texts: the International Classification of Diseases v.10 (ICD-10), and the Diagnostic and Statistical Manual of Mental Disorders v.4 (DSM-4-TR). The ICD-10 is an international classification vigorously tested and used world-wide. The DSM-4 was developed in the USA but is used also internationally. Over past reviews and versions of the two texts the diagnostic criteria used for determining a mental illness or disorder have developed greater similarities than variances.In the next two posts an explanation will be given about each of the diagnostic texts in common use. However, among Mental Health Services in NSW it is more common for the ICD-10 to be used as the text for diagnosis and differential diagnosis.