2 Identifying and diagnosing autistic conditions
2.1 Principles of diagnosis
The starting point for all systematic work on ASDs, whether in the field of research, therapy or education, is a clear and agreed description of characteristic patterns of symptoms for use in diagnosis. Accurate diagnosis is necessary to ensure shared understanding about the nature and implications of a individual's problem, and serves as the first step in establishing an appropriate basis for care and support for the individual and his or her family.
Underlying the use of systematic descriptions of autism in diagnosis is a framework of assumptions known as the diagnostic approach – an important tool in general medicine as well as in clinical psychology and psychiatry. Research and practice within this framework has provided evidence that particular psychological symptoms consistently group together to form identifiable clusters or syndromes, and has helped to elucidate the underlying causes of some of these clusters. Though the diagnostic approach assumes that syndromes are separable, it also accommodates overlap between their respective symptoms. For instance, lack of responsiveness to human voices could be a symptom of autism or of a hearing impairment. Differential diagnosis between these conditions depends on weighing up the overall pattern of symptoms. This is a necessary pre-requisite for establishing therapeutic needs: a hearing-impaired child has different needs from a child with autism.
Diagnosis: The process of placing an individual's pattern of symptoms as reliably as possible within a recognised category, for purposes of identification, research and treatment.
Diagnostic approach: Approach within clinical psychology and psychiatry involving the systematic description and classification of symptom patterns and their use in the identification and treatment of psychological problems.
Differential diagnosis: Use of diagnosis to distinguish between problems or conditions that have similar or overlapping sets of symptoms.