A study examining changes to the American Psychiatric Association's diagnosis guidelines predicts that estimates of the number of people with autism spectrum disorder are now likely to be lowered.
The fifth edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders - commonly known within the medical profession as DSM-5 - was published in 2013.
The previous edition, DSM-4, introduced several sub-types of autism spectrum disorder (ASD): autistic disorder, Asperger disorder, Rett disorder, childhood disintegrative disorder and pervasive development disorder not otherwise specified.
DSM-5, however, does not recognize different sub-types, only distinguishing between two ASD categories - "impaired social communication" and restricted, "repetitive patterns of behavior interests or activities."
The diagnostic criteria also now allow historical behaviors from the patient to be taken into account alongside current behaviors.
How do the new criteria affect current ASD estimates?
Some experts think that the new DSM-5 criteria require a higher threshold of symptoms, with some studies reporting that patients who previously met the DSM-4 ASD criteria would now be considered ineligible for the same diagnosis.
This new study, which is published in the Journal of the American Academy of Child and Adolescent Psychiatry (JAMA Psychiatry), set out to test that assumption and investigate what impact these new diagnostic criteria might have on people diagnosed with ASD.
The authors of the study applied the new DSM-5 criteria to data that had been collected by the Autism and Developmental Disabilities Monitoring Network. The data concerned 6,577 8-year-old children who had been diagnosed under the DSM-4 criteria as having ASD. Of these children, 81% (5,339) would retain their diagnosis under the DSM-5 criteria.
The study also applied the new DSM criteria to figures reporting how many people were diagnosed with ASD in 2008. Whereas those figures previously reported an estimate that 11.3 in 1,000 people meet the criteria for ASD, under the new diagnostic criteria this drops to 10 in 1,000.
What impact could the new criteria have on ASD services and diagnoses?
Although these figures suggest a large drop in diagnoses, the authors of the study acknowledge that take-up of the new criteria will not be instant, as clinicians' awareness of the revisions will be gradual. The authors also think it may be possible doctors will document additional symptoms in order to secure an ASD diagnosis when they believe it is required.
"Although the focus of this study was on prevalence, there were some noteworthy findings that could pertain to service eligibility," the study's author, Dr. Matthew Maenner, told Medical News Today.
"Children identified as having ASD by a health care or education professional were more likely to meet DSM-5 criteria than children with DSM-4 documented symptoms of ASD, but not an ASD diagnosis. Also, a large majority of children who did not meet DSM-5 criteria were lacking only a single symptom - that is, they had 4 of 5 required symptoms," he added.
Despite the study's predictions that estimates reporting the prevalence of ASD may drop as the DSM-5 revisions are taken up, the authors also acknowledge that future changes in the way ASD is evaluated and reported could counterbalance this:
"Autism spectrum disorder prevalence estimates will likely be lower under DSM-5 than under DSM-IV-TR diagnostic criteria, although this effect could be tempered by future adaptation of diagnostic practices and documentation of behaviors to fit the new criteria."
In 2013, JAMA Psychiatry also published a study on how DSM-5 criteria changes will affect the diagnosis of toddlers with ASD.