Sunday, April 11, 2010

A Dimensional Approach to Autism

The pervasive developmental disorders (PDD) have traditionally been viewed as categorical diagnoses. With a categorical or dichotomous scheme, disorders are either present or absent. For example, the DSM-IV-TR and ICD-10 list specific criteria for each disorder that must be met to receive a diagnostic classification. Similarly, the Individuals with Disabilities Education Act (IDEA) specify categories of special education disability. Both are categorical rather than dimensional systems of classification (e.g., a child meets or does not meet criteria) and both focus on a description of behavior rather than function.
       We now question whether autism should be conceptualized as a distinct clinical entity or as a continuum of severity. For example, children with the same diagnostic classification are likely to be heterogeneous and many childhood disorders, including autism, fall along a continuum in the general population. Categorical classification fails to account for these quantitative differences between children with the same core symptoms. In fact, there is a growing consensus among professionals who work with children with PDD that the differences between the higher functioning subtypes are not particularly useful in terms of either intervention or outcome and that autism is more appropriately conceptualized as a spectrum condition rather than an “all-or-nothing” diagnostic entity. We also recognize that traits similar to those observed in PDD are not restricted to children with a clinical diagnosis. This is especially important because even mild degrees of autistic symptomatology can have an adverse effect on a child’s adaptive and school functioning. Thus, while categories are much easier to conceptualize, they tend to be of minimal use in actual practice.
       This dimensional perspective is reflected in the American Psychiatric Association’s recently released draft diagnostic criteria for the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM). Specifically, the proposal for a new category of “autism spectrum disorder,” which incorporates the current diagnoses of autistic disorder (autism), Asperger’s disorder, childhood disintegrative disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS). This single “spectrum disorder” better describes our current understanding about the clinical presentation and course of the pervasive developmental disorders (PDDs), and should facilitate more effective identification and treatment going forward.

Wilkinson, L. A. (2010). A best practice guide to assessment and intervention for autism and Asperger syndrome in schools. London: Jessica Kingsley Publishers.

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