Autism, autistic spectrum and the need for better definition
The increase in prevalence might indicate a true increase in incidence, but most of the increase can be accounted for by changes in case-finding methods and diagnostic criteria, and by differences in sample sizes, and the age range and intellectual ability of the populations studied.
Abstract
AUTISM IS a severe neurodevelopmental disorder associated with considerable personal suffering, parental burden and community cost. In recent reports, the prevalence of autism has varied widely from five to 67 cases per 10 000 children, an increase compared with the 3.5–4.5 cases per 10 000 children reported in the 1970s.1,2 This apparent prevalence increase has raised considerable public concern, particularly as it has been temporally linked to the introduction of the measles–mumps–rubella (MMR) vaccine. However, recent epidemiological investigations found no causal link between autism and the MMR vaccine.3,4 The increase in prevalence might indicate a true increase in incidence, but most of the increase can be accounted for by changes in case-finding methods and diagnostic criteria, and by differences in sample sizes, and the age range and intellectual ability of the populations studied.3 The increase in numbers identified has led to a corresponding increase in demand for services. The predominant international approach to diagnosis used by the ICD-10 classification of mental and behavioural disorders5 and the Diagnostic and statistical manual of mental disorders, 4th edition [DSM-IV],6 groups autistic conditions in the category pervasive developmental disorder (PDD) and specifies criteria for the subtypes autistic disorder, Asperger’s disorder and atypical autism (PDD – not otherwise specified [PDD-NOS]) (Box). Recently, some confusion has been introduced, as there is a general move away from the term PDD towards the term autistic spectrum disorder (ASD), which has been used in at least four different ways.