Unpacking the Complex Nature of the Autism “Epidemic”?

The upcoming issue of Research in Autism Spectrum Disorders includes an article entitled Unpacking the Complex Nature of the Autism Epidemic. Judging from the fact that it is a 7-page article only, I didn’t expect it to really unravel the complicated matter surrounding the increase in autism diagnosis over the years, and I was right.

The article starts by summarizing that autism spectrum disorders are a group of conditions marked by the triad of impairments. The authors remain neutral on the subject of causation, citing sources that postulate genetic causes as well as various environmental factors, and concluding that there is likely an interplay between both and that there is no single cause for autism.

Notwithstanding the title of their publication, the authors remain inconclusive, but lean towards believing there is no actual autism epidemic. This is clear from the rest of their article, in which they examine various factors which could’ve influenced increases in diagnosis rather than actual increases in autism prevalence:

• Changing diagnostic criteria: the diagnostic criteria for ASDs have been broadened significantly since the DSM-III in 1980, thereby allowing for more diagnoses to be made. One study they cite even estimates a 2-0 to 28-fold increase in prevalence explained by changing diagnostic criteria.
• Nomenclature: the authors warn readers to use specific terminology. “Autism” can mean “autistic disorder”, which is different from “autism spectrum disorder”, which is yet different from “pervasive developmental disorder”. The terminology used influences prevalence rates.
• Age of diagnosis: apparently, if children are diagnosed at an earlier age, this artificially inflates the prevalence rate of autism.
• Methodological considerations: as clinicians become more aware of ASD and how to detect it, they are easier able to diagnose autistics.
• Socio-cultural factors: people have an incentive to get an ASD diagnosis, because it will get them services. Furthermore, in areas with more pediatricians, more children are diagnosed with ASD. Working class or poor children and black children are also less likely to be diagnosed with ASD than white children or those from the middle or upper class.
• Diagnostic substitution: this involves the diagnosis of ASD as one’s primary disability where previously something else would have been diagnosed, such as intellectual disability or a learning disability. One study even found a comparable decrease in the prevalence of intellectual disability to the increase in ASD prevalence. Others found that the increase in ASD diagnoses was at least in part compensated by a decrease in diagnosis of another (primary) disability. The authors conclude that it has yet to be answered whether some children would truly in the past have been diagnosed with another disability rather than ASD – as one study of adults diagnosed with developmental language disorder found.

The authors, finally, don’t answer the question of whether ASD is truly increasing. They don’t seem to believe in an epidemic, but that doesn’t mean some factors couldn’t lead to a modest increase in ASD prevalence.

Reference

Leonard H, Dixon G, Whitehouse AJO, Bourke J, Aiberti K, Nassar N, Bower C, Glasson EJ (2010), Unpacking the Complex Nature of the Autism Epidemic. Research in Autism Spectrum Disorders, 4(4):548-554. DOI: 10.1016/j.rasd.2010.01.003