2 Hypotheses: Autism Epidemic and Diagnostic Substitution
April 8, 2008 by Kristina Chew, PhD
Filed under Health
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?)
No statement.
Just thought these were relevant and might be of interest.
Edelson, M.G., (2006). Are the Majority of Children with Autism Mentally Retarded? A Systematic Evaluation of the Data.
Focus on Autism and Other Developmental Disabilities, v21 n2 p66-83 Sum 2006
There are frequent claims in the literature that a majority of children with autism are mentally retarded (MR). The present study examined the evidence used as the basis for these claims, reviewing 215 articles published between 1937 and 2003. Results indicated 74% of the claims came from nonempirical sources, 53% of which never traced back to empirical data. Most empirical evidence for the claims was published 25 to 45 years ago and was often obtained utilizing developmental or adaptive scales rather than measures of intelligence. Furthermore, significantly higher prevalence rates of MR were reported when these measures were used. Overall, the findings indicate that more empirical evidence is needed before conclusions can be made about the percentages of children with autism who are mentally retarded.
http://www.willamette.edu/dept/comm/reprint/edelson/
Interesting discussion related to Kanner, etc.
GERNSBACHER, M. A., GEYE, H. M., & ELLIS WEISMER, S. (2005).
The role of language and communication impairments within autism.
In P. Fletcher & J. C. Miller (Eds.), Language disorders and developmental theory.
Philadelphia, PA: John Benjamins.
http://psych.wisc.edu/lang/pdf/gernsbacher_chapter.pdf
More discussion of intelligence, testing, and what is being measured.
DAWSON, M., SOULIÈRES, I., GERNSBACHER, M. A., & MOTTRON, L. (2007).
The level and nature of autistic intelligence. Psychological Science, 18, 657-662.
http://psych.wisc.edu/lang/pdf/Dawson_AutisticIntelligence_PS_2007.pdf
Based on what studies are these test reliable forecasting tools on future potentials of the child taking them? Have there been any follow-up studies for comparison after 2003? I have heard little to nothing about the use, benefit, or administration of either of these tests in school systems or ASD populations in my geographic region.
Laurentius, i totally agree that IQ levels for autistics are underestimated.
Could it be that there in not an epidemic bout look like an epidemic becaue the rules may haved changed over the years. Do think that the first DSM-1 may have been too norrow and how that we up to DSM-1V maybe they just loosened the diagnosis that may enclue other things like alcohol systrom, nitrate poison {from well water on farms} whitch would bring up the count. I am not sure how they tell the difference of if you can tell the difference between that and autism.
Just more data…
FYI: Coo H, Ouellette-Kuntz H, Lloyd JE, Kasmara L, Holden JJ, Lewis ME. (2008). Trends in autism prevalence: diagnostic substitution revisited. Journal of Autism and Developmental Disorders, 38, 1036-1046.
There has been little evidence to support the hypothesis that diagnostic substitution may contribute to increases in the administrative prevalence of autism. We examined trends in assignment of special education codes to British Columbia (BC) school children who had an autism code in at least 1 year between 1996 and 2004, inclusive. The proportion of children with an autism code increased from 12.3/10,000 in 1996 to 43.1/10,000 in 2004; 51.9% of this increase was attributable to children switching from another special education classification to autism (16.0/10,000). Taking into account the reverse situation (children with an autism code switching to another special education category (5.9/10.000)), diagnostic substitution accounted for at least one-third of the increase in autism prevalence over the study period.
Linking to the Pubmed abstract because there are related articles in the sidebar–it’s a body of evidence, not necessarily the citing of one particular paper.
Interesting that the “reverse situation” of children with an autism code switching to another special education category was also studied.