Bishop, D. V. M., Whitehouse, A. J. O., Watt, H.J., & Line, E. A. (2008). Autism and diagnostic substitution: evidence from a study of adults with a history of developmental language disorder. Developmental Medicine & Child Neurology, 50(5), 341-345.
Aim of the paper:
Autism rates have risen over the past three decades. The ‘diagnostic substitution hypothesis’ says that this is because children that had previously been diagnosed with a different disorder are now being diagnosed with autism. This is because the diagnostic boundaries for autism have been broadened. Developmental language disorder (DLD) has similarities to autism, such as communication problems. This study aimed to find out whether a sample of 38 people diagnosed with DLD five to 25 years ago might now be diagnosed with autism. Two diagnostic instruments for autism were used; the Autism Diagnostic Observation Schedule – Generic (conducted by an examiner), and the Autism Diagnostic Interview – Revised (filled out by the participants’ parents).
What was found:
When a diagnosis required a score above threshold on only one of the instruments, 19 of the 20 people with pragmatic language impairment (PLI), and six of the 18 people with specific language impairment or DLD fit this criterion.
When a diagnosis required a score above threshold on both of the instruments, eight of the 20 people with PLI and none of the people with SLI/DLD fit this criterion.
What does this mean?
Overall, this study indicates that many children diagnosed with severe language disorders in the 1980s and 1990s, particularly those with PLI, might now be diagnosed with autism based on contemporary criteria. This provides direct evidence of diagnostic substitution. One explanation discussed was the idea that a diagnosis was not given due to a lack of problematic behaviour. At the time of language disorder diagnosis, autism was often only diagnosed if provision was considered necessary. This may not have been the case with these children. In conclusion, this study emphasises the lack of a clear dividing line between language disorders and autism. Importantly, the authors also note that studies conducted with children with language disorders need to be re-evaluated, as they may now be regarded as having ASD instead.
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