Pervasive developmental disorders in young children.

Abstract

THERE IS MUCH CONCERN ABOUT WHETHER THE PREVAlence of pervasive developmental disorders (PDDs), sometimes referred to as autistic spectrum disorders, is increasing. No study is likely to answer that question because the last 20 years have seen dramatic changes in the diagnostic criteria, an increase in public awareness of autism and related disorders, and sweeping changes in the types and availability of therapeutic and educational services. However, problems with determining whether prevalence of the PDDs is increasing should not serve to distract from the question that can be answered—ie, what is the prevalence of PDDs now. Determining the prevalence of a behaviorally defined disorder is more difficult than determining the prevalence of conditions for which biological markers exist. The symptoms of PDDs—deficits in social reciprocity and communication and restricted and repetitive behaviors—vary in severity and may appear quite different in children with different cognitive abilities. Autism, Asperger syndrome, and pervasive developmental disorder-not otherwise specified (PDD-NOS) have been proposed to occur along a spectrum within PDD. Autism, the most severe form of PDD, was estimated to have a general population prevalence of 4 to 5 per 10000 prior to 1988, according to surveys of children and adolescents. Prevalence studies using current diagnostic formulations and tiered screening of regional populations of preschool children have reported prevalence rates for the specific diagnosis of autism of 21 to 31 per 10000 and of 57.9 per 10000 for all PDDs combined. One small, regionally defined study of 7-year-olds reported rates for autism as high as 60 per 10000 and for all PDDs reported 121 per 10000. In a recent case finding study in Brick Township, New Jersey, the prevalence of autism was reported to be 40 per 10000 and for all PDDs it was reported to be 67 per 10000 with similar rates identified for children between the ages of 3 and 5 years and 6 and 10 years. The age of the sample and methods of case ascertainment may affect the prevalence rates reported in such studies. In this issue of THE JOURNAL, Chakrabarti and Fombonne report a prevalence rate in the United Kingdom of 16.8 per 10000 for autism and 63 per 10000 for all PDDs in a regional sample of children younger than 5 years. The identification of developmental concerns was aided by health visitors, specialized nurses who assist in monitoring health and development when a child is approximately 7 months, 18 to 24 months, and 3 years of age. Children with delayed or atypical development were referred to a multidisciplinary team who used the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM IV) criteria to establish the diagnosis of PDD. Children identified as having PDD on clinical grounds were further evaluated using the Autism Diagnostic Interview-Revised, a semistructured interview valid for establishing the diagnosis of PDD and autism in children as young as 18 months. Chakrabarti and Fombonne provide further evidence that PDDs are more common in preschool children than was previously thought, even when case finding occurs only through careful clinical evaluation. Just as newer studies are indicating higher prevalence rates for PDDs than were reported in earlier studies, they also indicate lower rates of mental retardation in children with PDDs. Only 26% of the children studied in the report by Chakrabarti and Fombonne were diagnosed with both PDDs and cognitive limitations. These were primarily children who met diagnostic criteria for autism. This finding agrees with the observations from other studies showing that 45% to 60% of young children with nonautistic PDDs have intellectual abilities in the normal range. Chakrabarti and Fombonne reported that evaluations looking for an origin for the disorder were guided by clinical judgment. Ten percent of the children had medical conditions identified. This is not dissimilar from the average rate of 6% of patients with medical conditions that might be related etiologically across 23 epidemiologic studies of children and