The DSM-IV (2) definition of autism was developed on the basis of a very large, international, multisite field trial. This definition retains historical continuity with previous definitions of autism but differs from its immediate predecessor in that age of onset (before age 3 years) is included as a necessary diagnostic feature and criteria are more conceptually framed. Diagnostic criteria are presented in Table 5.1.1.1.

The characteristic social and communicative deficits are believed to be aberrant relative to the person’s developmental level (1); consistent with Kanner’s original report and subsequent research, social difficulties in autism are a key diagnostic feature 4,5,6. Complexities for definitions of autism have included the broad range of syndrome expression, changes in syndrome expression with age, and differentiation from other psychiatric and developmental disorders 3,6.

Kraeplin’s description of dementia praecox was rapidly extended to children, and the terms childhood schizophrenia and childhood psychosis became synonymous. Early assumptions that all severe childhood disturbance must be a form of schizophrenia were based, in large part, on severity. Kanner’s 1943 (4) description of 11 cases of “early infantile autism” noted various ways in which this disorder appeared to be distinctive. These cases exhibited an apparently congenital inability to relate to other people (in contrast to an apparent ability and overconcern with the nonsocial environment); their language (when it developed at all) was remarkable for echolalia, pronoun reversal, and concreteness. Behaviorally, these children engaged in repetitive, apparently purposeless activities (stereotypy), and were intolerant of change. Kanner’s use of the term autism was meant to convey the unusual, self-centered quality that his cases exhibited, but it was also suggestive of the autism associated with schizophrenia. Although Kanner’s description has been remarkably enduring, early speculations about certain aspects of the condition (e.g., normal levels of intelligence, lack of association with other medical conditions, unusual levels of parental education) proved incorrect (3). The validity of autism was established over the next several decades only, as various lines of evidence became available (3). Autism was included in the landmark third edition of the DSM (DSM-III) (7). The initial definition of the condition in DSM-III lacked an appreciation of developmental change and was modified
in DSM-III-R (8). Unfortunately, while DSM-III-R was more developmentally organized, it proved problematic as it appeared that the diagnostic construct was overly broadened (3). As a result, substantial revisions were made in the DSM-IV (6). Table 5.1.1.2 summarizes historical highlights in the development of the concepts of childhood psychosis and autism.

More than 40 epidemiological studies have been published; in his review, Fombonne (9) reports prevalence estimates in studies conducted since 1987 ranging from 2.5 to 72.6 per 10,000 with a median rate of 11.3 per 10,000. There does appear to be an increase in reported prevalence over time, although several factors complicate the interpretation of this observation. For example, there is more public awareness of autism, and criteria for the condition have been changed and probably effectively broadened the concept. Furthermore, the lay press and public often equate the notion of “autism spectrum disorder” with more strictly defined autism (10). Other factors accounting for discrepancies include differences in screening and ascertainment procedures, and the size of target populations (with higher rates generally reported in studies with smaller samples). Although an increase in reported rates might reflect an actual increase in incidence, other factors, such as case definition and recognition, are important. Thus, newer studies are more likely to adopt broader definitions of autism. Selected epidemiological reports are summarized in Table 5.1.1.3.