Rise in autism related to changes in diagnosis, New study suggests

Over the past 10 years the prevalence rates have risen steadily, from one in 150, to one in 110, and now to one in every 88 children. This represents a 78 percent increase in the number of children identified with an autism spectrum disorder (ASD) over the past decade. What are the reasons for this dramatic increase in the prevalence of ASD? A new study suggests that the rise in the number of cases of autism may be related to changes to autism diagnostic criteria.

The criteria for assessing autism has changed over the last 20 years resulting in a broadening of autism diagnoses and the identification of cases that would not have been diagnosed by using older criteria. The current study published online in the Journal of Autism and Developmental Disorders re-examined diagnostic data from a state-wide autism prevalence study (n = 489) conducted in the 1980s to investigate the impact of broader diagnostic criteria on autism spectrum disorder (ASD) case status. Clinicians in the original study used DSM-III criteria to assess individuals as “diagnosed autistic” or “diagnosed not autistic.”  After applying current diagnostic criteria from the DSM-IV-TR to records from participants in the two-decades-old study, sixty-four (59 %) of the 108 originally “Diagnosed Not Autistic” met the current ASD case definition, while those who were found to have autism in the 1980s study continued to qualify for the diagnosis using the current criteria. The average IQ estimate in the newly identified group was also significantly lower than in the original group. Current diagnostic criteria applied to participants ascertained in the 1980s identified more cases of autism with intellectual disability. The researchers conclude, “The results of this study demonstrate a significant effect on ASD case status attributable to changing ASD criteria, particularly with regard to individuals with intellectual impairment,” They also comment, “An important caveat, however, is that we were unable to determine whether it was the broadening of the criteria themselves, or the interpretation of the criteria, which lead to this effect.”

The current study supports the theory that the rise in the number of cases of autism may be related to changes in how the disorder is diagnosed. Another aspect of the autism landscape that has changed over the past 20 years is an increase in the awareness of autism among the general public as well as healthcare professionals. While recent findings suggest that at least a portion of the increase in prevalence can be attributed to these factors, they cannot alone explain the dramatic rise in autism prevalence. According to Autism Speaks, genetic vulnerabilities and interaction with environmental factors are likely contributors to the increase in prevalence. 

Miller, J. S., Bilder, D., Coon, H., Pinborough-Zimmerman, J., Jenson, W., Rice, C. E., Fombonne, E., Pingree, C. B., and Ritvo, E., et al. (2012). Autism spectrum disorder reclassified: A second look at the 1980s Utah/UCLA Autism Epidemiologic Study. Journal of Autism and Developmental Disorders. DOI: 10.1007/s10803-012-1566-0

Lee A. Wilkinson, PhD, CCBT, NCSP is author of the award-winning book, A Best Practice Guide to Assessment and Intervention for Autism and Asperger Syndrome in Schools, published by Jessica Kingsley Publishers