Module 3 - Assessment of Mental Health for People with an Intellectual Disability

Classification of Mental Illness

Classification of illnesses is a way of giving names to different illnesses and conditions. Doing this helps to decide what is wrong with a person and what treatment they may need. Some medical conditions are classified on the basis of the cause, such as bacterial meningitis, others on the basis of the structural changes in the body, such as a heart attack or myocardial infarction.  In other cases illnesses are classified on the basis of the symptoms they present with, such as migraine headaches, and still others on the basis of how different they are from most people, such as hypertension (high blood pressure). In general, classification based on the cause of the problem has proven to be most useful in clinical practice. For example pneumonias (infections of the lungs) could be classified on the basis of their symptoms such as cough, temperature, etc. but it is only by identifying the bacteria causing the problem that an appropriate antibiotic can be selected. Unfortunately the cause of most mental disorders is unknown and most mental disorders are classified by recognising patterns of symptoms (patterns of symptoms that occur together are called syndromes and are thought to indicate particular illnesses). It is hoped that categorising mental illness on the basis of syndromes will eventually lead to identifying the causes underlying the different diagnoses. One of the consequences of classifying mental illnesses in this way is that of unreliability. There is no diagnostic test that can prove a diagnosis and the accuracy of the diagnosis depends on the skill of the clinician in eliciting symptoms and correctly applying these to the appropriate illness categories. There is much room for error in this process and psychiatrists may differ in their opinion regarding the diagnoses for a particular patient. The major classification system used in Australia is the Diagnostic and Statistical Manual of Mental Disorders, now in its 5th Edition (DSM–V) produced by the American Psychiatric Association. In Europe the International Classification of Diseases is used, which is in its 10th edition (ICD-10). The Diagnostic and Statistical Manual of Mental Disorders divides mental illness into a number of categories, these being: Disorders usually first diagnosed in infancy, childhood or adolescence (Developmental disorders) Neurocognitive disorders (including delirium and dementia); Mental disorders due to a general medical condition; Substance-related disorders; Schizophrenia and the other psychotic disorders; Mood disorders (including depressive and bipolar disorders); Anxiety disorders; Somatoform disorders;  Factitious disorders; Dissociative disorders; Sexual and gender identity disorders; Eating disorders; Sleep disorders; Impulse control disorders; Adjustment disorders; Personality disorders; and Other conditions that may be a focus of clinical attention. Many of these will be discussed further in subsequent modules.
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