To what extent has the prevalence rate of autism increased because of the “better diagnosis” argument—-that we are able to better diagnose and identify autism today than in the past? Is what some call an “epidemic of autism” more accurately described as a sort of “epidemic of understanding and awareness” about autism?
A new study in the Developmental Medicine and Child Neurology by Dorothy Bishop, et al., has found that some adults who received a diagnosis of language disorder during childhood might now have been diagnosed with autism. 38 adults (age 15 to 31) were included in the study, whose findings Translating Autism by Nestor L. Lopez-Duran, Ph.D., cogently summarizes:
The authors were mostly interested in a particular type of language disorder diagnosis called pragmatic language impairment (PLI), since this disorder has many similarities with autism. The authors conducted full ADOS and ADI evaluations of these individuals. They found that 55% of the participants with PLI met the criteria of autism as indicated by the ADOS or the ADI, and 40% met the criteria of autism as indicated by both, the ADOS and the ADI.
These findings are consistent with the diagnostic substitution of autism. The implication is that a significant percentage of people who were diagnosed with PLI in the past would now receive a diagnosis of autism instead. Likely this substitution is not sufficient to explain, in its entirety, the dramatic increase in autism diagnoses; but it is reasonable to conclude that such substitution could partially explain such increase. In addition, the PLI substitution is just one of several proposed substitutions (see for example MR as described here). Finally, it could be argued that these individuals received the correct diagnosis of PLI as children and developed autism symptoms as adults. Although this is a plausible explanation, it is not consistent with what we know of the developmental progression of autism symptoms.
Professor Dorothy Bishop is quoted in a press release, which notes that the “two main hypotheses” to explain the rise in the autism rate are the “autism epidemic” hypothesis and the “diagnostic substitution” hypothesis.
“Our study shows pretty direct evidence to support the theory that changes in diagnosis may contribute towards the rise in autism,” says Professor Bishop. “These were children that people were saying were not autistic in the 1980s, but when we talk to their parents now about what they were like as children, it’s clear that they would be classified as autistic now.
“Criteria for diagnosing autism were much more stringent in the 1980s than nowadays and a child wouldn’t be classed as autistic unless he or she was very severe. Now, children are being identified who have more subtle characteristics and who could in the past easily have been missed.”
However, Professor Bishop cautions against using the results to suggest that the prevalence of autism is not genuinely rising.
“We can’t say that genuine cases of autism are not on the increase as the numbers in our study are very small,” she says. “However, this is the only study to date where direct evidence has been found of people who would have had a different diagnosis today than they were given fifteen or twenty years ago.”
Another way to think about the “autism epidemic” and “diagnostic substitution” hypotheses is this: Is the increase in the number of autism diagnoses (especially in children) due to some external factor or agent; to, for instance, something in the environment—-in the physical world—that has changed? Or, is the increase due to a kind of internal change in us, in how we think about and understand and perceive the world? Psychology is a relatively recent innovation: The ancient Greeks and Romans who I teach were certainly interested in how we humans think and what happens to our souls (the Greek word for soul is psyche) and whether we have one. What would we call “autism” in a time and a world without psychology? (And can you imagine such a perspective?)