For example, symptoms and characteristics change with developmental maturity and vary with the degree of associated cognitive impairment (Filipek et al., 1999a). This evolving pattern of clinical features can make the differential diagnostic process very difficult in some cases. Nonetheless, the defining feature of autism is the presence of a distinctive impairment in the nature and quality of social and communicative development (influenced by the specific biological and environmental circumstances of the individual). It is this impairment that distinguishes autism from other neuro-developmental conditions (e.g., mental retardation, developmental language disorders, and specific learning disabilities). For example, whereas mental retardation is characterized by a pervasive developmental delay, autism is characterized by a distinctive impairment in the nature of social-communicative development. The prognostic significance of this autistic social dysfunction is underscored by preliminary studies that report a negative correlation between the severity of this social impairment and treatment responsiveness, at least with regard to social and linguistic growth following intensive, behaviorally based early intervention (Ingersoll, Schreibman, & Stahmer, 2001).
Additional complexity in the differential diagnosis of autism and related PDDs results from a wide range of accompanying ab ...Show more