Objective: To examine empirical data on children with autistic disorder (AD), Asperger's disorder, and pervasive developmental disorder not otherwise specified (PDD-NOS) for continuities or distinguishing features between disorders and to see to what extent the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) diagnostic criteria reflect observed data. Method: Studies were identified in 4 ways. 1) A Medline search from 1976 to the present of articles with the key words autism, pervasive developmental disorder, autistic spectrum disorder, and Asperger; of these articles, those with mesh headings or textwords “cluster,” which identified cluster analyses deriving pervasive developmental disorder (PDD) subtypes, were retained. 2) The Journal of Autistic and Developmental Disorders from 1990 to the present was hand-searched to identify other empirically derived studies on diagnosis, prevalence, classification, and validity of PDD subtypes. 3) Key review articles were searched for their references. 4) The references of all identified articles were searched. Results: Eight cluster studies were retained for their relevance to diagnostic issues, as were 7 empirically derived studies delineating clinical characteristics of children with AD, Asperger's syndrome, or PDD-NOS. Data suggest that children with PDD may fit into 1 of 2 overlapping groups, including a lower-functioning group with greater developmental compromise, social aloofness, and a greater number of autistic symptoms and a higher-functioning group with higher IQ, fewer autistic symptoms, and more prosocial behaviour. The PDD subtypes resemble each other and can be seen as existing on a continuum, differing only by degree of impairment. Conclusion: Children exhibiting the triad of autistic impairments can be seen as suffering from disorders on a PDD continuum. While the DSM-IV does identify a lower-functioning autistic group (AD), the higher-functioning group is less well served. Asperger's disorder as defined in the DSM-IV is not clearly distinguishable from AD and PDD-NOS, and the PDD-NOS subcategory is not operationalized. Further research is required to elaborate criteria for the higher-functioning PDD group, and measures related to etiology, outcome, and treatment response may help determine which diagnostic criteria can meaningfully separate one disorder from another.
