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THE MERCK MANUAL MEDICAL LIBRARY: The Merck Manual of Medical Information--Home Edition
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Classification and Diagnosis of Mental Illness

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In 1952, the American Psychiatric Association first published the Diagnostic and Statistical Manual of Mental Disorders (DSM-I), marking the first attempt to approach the diagnosis of mental illness through standardized definitions and criteria. The latest edition, DSM-IV-TR, published in 2000, provides a classification system that attempts to separate mental illnesses into diagnostic categories based on descriptions of symptoms (that is, what people say and do as a reflection of how they think and feel) and on the course of the illness. Newer revisions of the DSM are expected to describe mental disorders along a continuous spectrum of symptoms, rather than classifying them by categories.

The International Classification of Disease, 10th Revision, Clinical Modification (ICD-10-CM), a book published by the World Health Organization, uses diagnostic categories similar to those in the DSM-IV-TR. This similarity suggests that diagnoses of specific mental illnesses are becoming more standard and consistent throughout the world.

Advances have been made in diagnostic methods. Several brain imaging techniques are available. They include computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET), a type of scan that measures blood flow to specific areas of the brain (see Symptoms and Diagnosis of Heart and Blood Vessel Disorders: Positron Emission Tomography). These imaging techniques are being used to map brain structure and function in people with normal and abnormal behavior, and they give scientists greater understanding of how the brain functions in people with and without mental illness. Research that has differentiated one mental health disorder from another has led to greater precision in diagnosis.

Last full review/revision May 2007 by Caroline Carney Doebbeling, MD, MSc

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