In 1980, the term pervasive developmental disorder (PDD) was introduced into the child psychiatric classification to describe children whose developmental difficulties cross multiple developmental lines (see Box 107.1 for the historical perspective of Autism). This category has been substantially expanded from one specific disorder in the original 1980 classification, autistic disorder, to the inclusion of several other conditions in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR). The conditions described as PDD in both the International Classification of Diseases, Tenth Edition (ICD-10), and in DSM-IV–TR are autistic disorder, Rett syndrome (see Chapter 98, Mental Retardation), childhood disintegrative disorder, Asperger syndrome, and unspecified forms of PDD. An additional diagnosis, overactivity associated with mental retardation and stereotypical movements, is included in ICD-10. Autistic disorder is described here; the DSM-IV–TR and ICD-10 classifications should be consulted for the other conditions.

The syndrome of autistic disorder, in which social, language, cognitive, imaginative and behavioral deficits are apparent, is the prototype of DSM-IV-TR PDD. The relationship between cognitive and language deficits and social abnormalities has been a focus of research. As shown in Box 107.2, diagnostic criteria for autistic disorder have been introduced that focus on qualitative impairments in social interactions and in interpersonal communication, along with a stereotyped restricted pattern of interests and activities. These abnormalities affect functioning in all situations and, in most instances, are present from infancy onward. The disorder is most commonly recognized in the second year of life, but may be recognized up to
approximately 30 months of age. The disorder is defined in terms of behavior that is deviant in relation to the child’s mental age. The majority of children with this disorder have intellectual disability as a feature of their PDD. Efforts are ongoing to identify additional subgroups within this category.

Confusion sometimes exists about the language disorder in PDD, related to the dual nature and function of language. Language serves the purposes of being a mental tool in thinking and also the primary means of communication with others. Children with PDD have the greatest difficulty with the practical use of language as a communication tool (pragmatic language). The language disorder is in social communication (i.e., in appropriately conversing with others). Difficulty in sharing experiences with others (social reciprocity) is a characteristic feature of PDD, regardless of the child’s intellectual level. Communicating feelings poses a particular problem because of the child’s difficulty in interpreting the meaning of tone of voice, posture, and facial expression in others in a social context. Additionally, to share the other person’s frame of reference requires memories of one’s own emotional experience. Remembering and sharing affective experience also is a problem. Deficits exist not only in initiating verbal social communication but also in understanding the nonverbal communication of others.