SIGN Guideline 98: Assessment, diagnosis and clinical interventions for children and young people with autism spectrum disorders

2 Definitions and concepts

2.1 DEFINITIONS

The term autism spectrum disorders has been used throughout this guideline to cover conditions termed autism, atypical autism and Asperger’s syndrome (see annex 2). These are complex developmental disorders, behaviourally defined, that include a range of possible developmental impairments in reciprocal social interaction and communication, and also a stereotyped, repetitive or limited, behavioural repertoire. ASD may occur in association with any level of general intellectual/ learning ability, and manifestations range from subtle problems of understanding and impaired social function to severe disabilities.¹

Impairments in each of the areas relevant to ASD diagnoses occur along a continuum from minimal to severe and categorical diagnoses inevitably involve defining a cut off. Diagnostic classification in itself should not be the basis for decisions about provision within education, or needs for social care and support.²

2.2 DIAGNOSTIC CRITERIA

There are two major diagnostic classification systems in current use, the International Classification of Diseases, version 10 (ICD-10)¹¹ and the Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV).¹² They have similar symptom criteria for diagnosis, based on a triad of impairments, with the behaviours being discrepant from the individual’s mental age:^{13, 14}

social – impaired, deviant and delayed or atypical social development, especially interpersonal development
language and communication – impaired and deviant language and communication, verbal and non-verbal. Impairment in pragmatic aspects of language
thought and behaviour – rigidity of thought and behaviour and impoverished social imagination. Ritualistic behaviour, reliance on routines, impairment of imaginative play.

A comparison of the two systems is given in annex 2.

ICD-10 (available in complementary clinical and research forms) is the most commonly used ASD classification system in the UK, although many research studies use DSM-IV or other criteria. For this reason and to minimise complexity, where differences of terminology occur between ICD-10 and DSM-IV, this guideline has used that within ICD-10.

The diagnostic criteria for ASD continue to develop as more research is done and understanding improves, and they are likely to change with future revisions. For example, for a diagnosis of Asperger’s syndrome, both systems require no clinically significant general delay in language (speech of words and phrases by specified times) and no clinically significant general delay in cognitive development. DSM-IV also employs an explicit hierarchy, so that Asperger’s syndrome can only be diagnosed if criteria for autism are not met. This is not specified in the same way within ICD-10.

Wider usage of diagnostic terms may be influenced by other factors and may not always reflect the definitions in classification systems. For example, the name Asperger’s syndrome may be used for some individuals who speak well later, but did in fact have early language delay.

There is limited evidence on the reliability and validity of the existing classification systems, ICD-10 and DSM-IV. Several studies have explored the discriminatory validity of Asperger’s syndrome and autism, but no studies have looked at predictive validity.

Three studies all found that the use of DSM-IV and ICD-10 criteria for autism improve the reliability of the diagnostic process.^15-17 The studies consistently found that:

using either DSM-IV or ICD-10 increases the reliability of the diagnostic process. The effect is even greater when inexperienced practitioners are making the diagnosis
the current criteria for Asperger’s syndrome and autism have poor discriminant validity.
Evidence level 2+

CAll professionals involved in diagnosing ASD in children and young people should consider using either ICD-10 or DSM-IV

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