In DSM-III (published by the APA in 1980) a new class of childhood onset disorders was identified. These were termed as Pervasive Developmental Disorders (PDD)¹¹. In many ways PDD is a clinical equivalent to the term ‘autistic spectrum’ with the addition of certain similar but less related conditions (such as Rett’s Syndrome). Individuals with a PDD were impaired in the growth and development of functioning over a wide range of areas and abilities. The term did not imply or rely on any presupposed assumption or theory of aetiology and did not consign such conditions to any specific individual discipline. As a class of disorder and in the use of diagnostic criteria PDD is still widely accepted and broadly used today. Among the other PDD’s was autism. Autism specifically was divided into two categories: Infantile Autism and Residual Infantile Autism. The latter of these categories was intended to encompass those individuals who fitted the criteria for infantile autism at one point but no longer did so completely. Generally however this was viewed as an inadequate response to developmental change and suggested autism was transient which is not the case. The severe impairment of social interaction was emphasised but so too was pervasive and profound deficits in the development of language. This was seen as inappropriate because although many individuals with autism demonstrate severe language impairments or are mute the underlying difficulty and impairment is seen to be one of communication. There was also a requirement that onset of the disorder be evident before the age of 30 months.

DSM-III was soon followed by DSM-III-R (the revised edition, APA, 1987)¹². The new diagnostic criteria for autism were broader and theoretically (and in practice in the evidence of field trials) encompassed many more cases then previously. The triad of impairments that is fairly universally recognised as the basis of autism and autistic spectrum disorders was included. These were a qualitative impairment in reciprocal social interaction; qualitative impairments in verbal and non-verbal communication, and in imagination; restricted repertoire of activities and interests. These were sub-divided and for a diagnosis of autism an individual had to conform to a minimum number of the sub-categories. The age of onset limit was dropped from DSM-III-R. The condition was renamed Autistic Disorder emphasising the life-long nature of autism. The changes to diagnostic definitions and criteria and to the necessity of an age of onset limit were seen as problematic as they broadened the classification, diverged from the original and current understandings and perceptions of the condition and complicated the validity and use of studies using other and previous concepts. As a result the description and criteria of autism was changed substantially for the subsequent APA publication DSM-IV¹³.

DSM-IV was published in 1994 and is generally regarded as a significant improvement on DSM-III-R¹⁴. Criteria and definitions were conceptualised in accordance with a concurrent diagnostic tool ICD-10 (see below) resulting in a fairly universal approach. The criteria for a diagnosis of autism (termed childhood autism) are reproduced under ‘DSM Criteria’.

The DSM-IV criteria also define other conditions as mutually exclusive to autism. These conditions include the other pervasive developmental disorders. There is also a category for atypical forms of autism which are not best categorised as another form of PDD. These include cases where most of the symptoms and sub-categories are complied to but there is a difference not accounted for by an alternative diagnosis, such as deviation in age of onset or in fulfilling the required number of criteria.

DSM-IV categorically refers to the triad of impairments of autism. Some degree of impairment must be present in each category (social interaction, communication, stereotyped behaviour) within a range of individual variation. More weight is given to the social interaction element of autism. This is in accordance with the overwhelming majority of views on autism and relates directly to Kanner’s ‘autistic aloneness’. The triad of impairments are discussed in detail later but it is clear that they form the basis of diagnosis and classification in autism. As important as defining the functional elements and presentations of autism is a recognition that autism is a condition. To some degree it may define how a person acts and behaves, and why they do so, but it does not define who a person is. People with autism are individuals with their own identity and personality to the same extent that non-autistic people are. This must be recognised in the diagnostic process. Behaviours and abilities will be manifest as a consequence of many factors, including personality, environment and other conditions or health-related concerns as well as autism itself. The importance of this issue cannot be illustrated or ensured through diagnostic criteria but emphasises how such criteria are useful only when constructively applied by experienced, understanding and sympathetic clinicians.

As previously mentioned DSM-IV is significant not solely for its advancement in criteria and definitions but also for its universally applicable nature. The is due to co-operation and agreement, as stipulated by formal convention, with the World Health Organisation’s ICD-10 (WHO, 1992, 1993).