Majority Of Autism Increase Due To Diagnostic Changes, Finds New Study
Almost two thirds of the increase in autistic Danish children results from how autism is diagnosed and tracked, found a new study in JAMA Pediatrics, lending more support to the idea that the apparent rise in autism rates, or at least most of it, is unlikely to be “real.” That is, the increase is likely more about previously-unidentified autistic individuals getting an autism diagnosis than more individuals actually developing autism.
Although the term “autism” has been around for more than a century, it didn’t start taking on a meaning we would recognize today until the 1940s, and it remained linked to schizophrenia, a completely unrelated psychiatric disorder, until the 1960s. The definition has continued to expand and become more detailed, and thus autism prevalence has been adjusted accordingly over the years.
In Denmark in particular, the diagnostic criteria for autism expanded in 1994 to include a spectrum of disorders with a broader list of symptoms, thereby widening the definition of autism. Then in 1995, national data tracking began to include diagnoses made from outpatient patient visits rather than just diagnoses of those admitted to a healthcare facility. Since every Danish resident has a complete health record maintained by the Danish government, researchers can use this national health registry to study an entire population with lower likelihood of bias from those included or excluded in a study.
By examining the health records of all children born in Denmark from 1980 through 1991 – nearly 668,000 children – the researchers determined that 60 percent of the increase in autism rates in Denmark could be attributed to those two changes in the way Danish autistic children have been counted since the mid-1990s. The change in the diagnostic criteria accounted for a third of the increase in autism, and including outpatient diagnoses in the statistics account for 42 percent of the increase.
What makes this study strong is its size, with well over a half million children born over a decade, and the use of the national health registry for the data. “The authors have at hand a more exhaustive and thorough database than is available pretty much anywhere else, and their findings are echoed by some other studies,” said Glen Elliott, chief psychiatrist and medical director of Children’s Health Council in Palo Alto, Calif. But it’s less clear, Elliott told me, how much these findings can be generalized to the U.S. Autism prevalence in Denmark, 54 of every 10,000 children, is still far lower than that of the U.S., with 147 of 10,000 children, though the latter, he said, uses a less precise tool* than direct access to patient records, as used in this study.
“Likely, the effect of diagnostic changes is similar between Denmark and the U.S., although we don’t really have side-by-side studies of which I’m aware to prove that,” Elliott said. “The effect of awareness and early detection of autism spectrum disorders could well be different between the two countries.”