Thursday, March 29, 2012

Autism and intellectual disability in DSM-5

Earlier this week, I wrote about the recently published study by McPartland, Reichow and Volkmar, looking at the potential impact of the proposed DSM 5 criteria for Autism Spectrum Disorder. There were caveats-a-plenty but the data suggested that autism rates may go down considerably as a result of the renegotiation of diagnostic borders. In fact, a new diagnosis, Social Communication Disorder, has been created to capture all the people who won't now make the ASD cut-off.

In the comments, an important question was raised by Harold Doherty, author of the Autism in New Brunswick blog: What will happen to autistic people with intellectual disability in DSM 5?

Although I didn’t mention it in the original post, this was actually something that McPartland et al looked at in their study.

Harold's concern, which he's been raising for some time, is that the wording of the new criteria will actually (and, in his view, deliberately) exclude people with an intellectual disability.

Under the draft version of DSM 5, in order to receive an ASD diagnosis, a person would have to show:
"persistent deficits in social communication and social interaction across contexts, not accounted for by general developmental delays." 
It's that last part that is the issue for Harold.

The idea, as I interpret it, is to make sure that people getting an ASD diagnosis really are autistic and not merely people who have social difficulties that are a result of developmental delay.

An analogy would be with people who are born deaf or blind; they inevitably have social interaction difficulties but we wouldn't necessarily call them all autistic. In the same way, someone with intellectual disability might struggle in certain social situations because of their poor language and memory skills, but again they wouldn't necessarily be considered to have autism.

Autism is more than just being a little behind in terms of social development. It’s qualitatively different. The challenge is to define those qualities.

This interpretation of the new criteria is entirely consistent with the quotation Harold provides from Cathy Lord, a member of the DSM-5 Neurodevelopmental Work Group:
Catherine Lord… said that the goal was to ensure that autism was not used as a “fallback diagnosis” for children whose primary trait might be, for instance, an intellectual disability or aggression. New York Times, 20 Jan, 2012 
Clearly, the intent is to stop non-autistic people getting an ASD diagnosis. That isn’t the same thing as saying that, if you’re intellectually disabled, you can’t also be autistic.

So much for the intentions. What about the guidelines in practice?

In one of their analyses, McPartland et al. divided people up according to their IQ. Those with IQs below 70 were considered to have “low cognitive ability”, which I think for our purposes we can treat as being synonymous with intellectual disability.

As in the previous post, I’ve plotted the results with kids achieving a DSM-5 ASD diagnosis in blue (ASD+) and those missing out on a diagnosis in red (ASD-).




As we saw last time, a good chunk of the kids failed to meet DSM-5 criteria for ASD. However, kids with intellectual disability were much more likely to be diagnosed with ASD than were those with IQs above 70. This is the opposite of what we’d expect if DSM-5 really was going to selectively exclude the intellectually disabled.

As I discussed before, we need to treat these findings with a good deal of caution. But I can't see any intention to exclude people with intellectual disability, and there's certainly no evidence at this time that this will happen in practice.


Reference:

McPartland JC, Reichow B, & Volkmar FR (2012). Sensitivity and Specificity of Proposed DSM-5 Diagnostic Criteria for Autism Spectrum Disorder. Journal of the American Academy of Child and Adolescent Psychiatry, 51 (4), 368-83 PMID: 22449643

Monday, March 26, 2012

How will DSM 5 affect autism rates?

In January, at a meeting of the Icelandic Medical Association, Yale researcher, Dr Fred Volkmar gave a presentation of data from a study looking at the implications of changes to autism diagnostic criteria in DSM 5. His conclusion was that many people who are currently diagnosed with autism, Asperger's, or PDD-NOS would not meet the new proposed criteria for autism spectrum disorder in DSM 5.

Volkmar's remarks were picked up by the New York Times, who ran with the lede:
"Proposed changes in the definition of autism would sharply reduce the skyrocketing rate at which the disorder is diagnosed and might make it harder for many people who would no longer meet the criteria to get health, educational and social services"
Not surprisingly, the article caused much consternation in autism circles. But because the study itself hadn't been published, members of the DSM 5 Neurodevelopmental Work Group, charged with implementing these changes, were unable to pass comment.

After all the brouhaha, the Yale study, with Dr James McPartland as first author, was finally published online two weeks ago - to suprisingly little fanfare. It was also accompanied by a commentary from Susan Swedo and members of the DSM 5 group, who had finally got hold of the paper.

DSM 5 and autism

A quick recap. There are essentially two big changes on the cards in DSM 5 as far as autism is concerned. First, rather than there being separate diagnoses of autistic disorder, Asperger's syndrome, and PDD-NOS, there will be a single category of "Autistic Spectrum Disorder".

Second, rather than organising the criteria into three themes, DSM 5 will collapse that down to two.

But there's also a more subtle and potentially more important change. DSM IV took a kind of pick'n'mix approach, with over 2000 combinations of 12 "symptoms" that would get you a diagnosis.
In DSM 5, this is simplified. The "symptoms" themselves are each somewhat broader and perhaps more flexibly interpreted, but there is much less scope for picking and mixing.

McPartland et al.'s study

Whether or not you agree with the changes in principle, what really matters is how the new criteria translate into the real world. There are currently ongoing "field studies" that are testing out the new criteria to see how they work in practice. McPartland and Volkmar essentially took a short cut by reanalysing the data from a similar field trial conducted 20 years ago when DSM IV was being developed.

To do this, McPartland et al had to translate the questions that were asked in the original study into something approximating an item in DSM 5. They then reanalysed the data, applying DSM 5 rules to "re-diagnose" the kids in the original study.

This is how things worked out. Kids in blue (ASD+) were those who met criteria for ASD in DSM 5. Those in red (ASD-) failed to meet the criteria.




As you can see, roughly three quarters of kids originally diagnosed with autistic disorder met DSM 5 criteria for ASD. However, only a quarter of those with a diagnosis of Asperger syndrome or PDD-NOS made the grade, so to speak.

These figures seem to back up Volkmar's claim that many people, currently diagnosed, would not meet the new criteria. However, with publication, the limitations of the study are now clear, as noted in the commentary by Swedo and colleagues, and by the authors themselves.

Limitations

The most obvious problem is that the original study was not designed for these purposes. While some of the DSM 5 criteria mapped neatly onto items in the original study, others didn't. For example, DSM 5 includes this pretty vague statement:
Symptoms must be present in early childhood (but may not become fully manifest until social demands exceed limited capacities).
Translated into English, this I think means that parents should be able to look back with hindsight and  recognise early signs of ASD, even if they missed them at the time. Quite how this will be ascertained without asking leading questions is not clear. But the important point is that there was nothing in the DSM IV questions that really corresponded to this question, so McPartland had to go with the nearest thing, which was "onset before 36 months".

As Swedo et al caution, it's probably best to wait until the results of the actual field studies are in. However, given that the DSM 5 criteria are much more prescriptive than those for DSM IV, we have to expect results along these lines. 

Further comment comes from David Skuse. Writing in his editorial capacity, he highlights the pressing issue of the people who don't meet the DSM 5 criteria. As mentioned in a previous post, DSM 5 is set to introduce a shiny new diagnostic category of "Social Communication Disorder" which would capture many of these people. The clinical and scientific merits of this new diagnosis are, however, yet to be established.

For me, this all highlights the inherent circularity and subjectivity of the DSM 5 debate. McPartland et al. effectively use DSM IV diagnoses as the standard against which to judge DSM 5. In the original trial 20 years ago, these would have been judged against DSM III. Inevitably the outcomes are slightly different, but who is to say which is better or worse? Swedo et al. make precisely this point, arguing that the true "gold standard" is expert clinical opinion. Or, to put it another way, we know it when we see it. An admission, perhaps, that autism defies definition.




Reference:

McPartland, J., Reichow, B., & Volkmar, F. (2012). Sensitivity and Specificity of Proposed DSM-5 Diagnostic Criteria for Autism Spectrum Disorder Journal of the American Academy of Child & Adolescent Psychiatry, 51 (4), 368-383 DOI: 10.1016/j.jaac.2012.01.007


Related posts:

Further reading: