Autism Identification Rates Continue to Rise

A CDC report issued shortly before Christmas found that autism rates surged 56% between 2002 and 2006. Coincidentally, 2006 is also the year in which the first drug approval was issued for a pharmaceutical used in the treatment of autism: namely, Risperdal.  This timing suggests that the increase in autism identification over this period was not straightforwardly related to pharmaceutical marketing (potentially excepting off-label marketing during this period). It is also important to note that this latest surge is part of an ongoing increase in the rate of autism diagnosis cast longitudinally over several decades.

The study’s lead author noted in the press that it is difficult to determine how much of the increase is attributable to an actual increase in autism among children, and how much is due to increased rates of detection.  This uncertainty, however, did not preclude speculation about some of the potential environmental causes of the condition presently under investigation, such as “exposure to hazardous pollutants and the added risk of parents giving birth at older ages”.

In the CDC study, children met the case definition for an Autistic Spectrum Disorder if their medical records documented behaviors consistent with DSM-IV-TR criteria for autistic disorder, pervasive developmental disorder–not otherwise specified (PDD NOS), or Asperger disorder. Children were classified as having a previously documented ASD classification if they had 1) received a diagnosis of autistic disorder, PDD-NOS, Asperger syndrome, PDD, or ASD by a qualified professional that was documented in an evaluation record or 2) had received special education services under an autism eligibility category. Reliability of previously documented ASD classifications is not discussed at any length in the report.

What is the social significance of increasing rates of autism identification?  Is this significance affected by whether or not these rates reflect an actual increase in true positives?  Is this trend likely to continue?  And finally, how is this trend likely to be affected by proposed changes to the Autism Spectrum currently under consideration for inclusion in the DSM-V?

CJ Murdoch

4 Responses to Autism Identification Rates Continue to Rise
  1. “or 2) had received special education services under an autism eligibility category.”

    That sounds like a potentially deceptive part of the definition. At least in the US, designation for special education services has a host of implications for the child and for the school district. Mark Kelman has written about how special education students are found at the highest rates in the poorest and the richest school districts – probably not because of higher incidence in at least the second of those locations.

    Do you know how many of the diagnoses were made on the second branch?

    More generally, do you think there is any good way to figure out how much of the apparent increase is real? Even professional diagnoses are likely to be affected by increased knowledge and prominence of the disorder.

    I find this is a very frustrating field because I really don’t hsve a clue as to whether the “true incidence” (however one defines that) of autism really is increasing.


  2. Hank, I agree with your intuition about special education, and for that reason I selectively mentioned it in the OP.

    Skimming back over the report, I don’t believe the ASD group is divided again in the analysis once the decision is made definitionally to aggregate the two branches. However, there is this loosely related finding of interest:

    “For sites that had full access to education records, information in the records indicated that the vast majority of children identified with an ASD for surveillance were receiving special education services through public schools (Table 3). Wide variation existed in the proportion of children who were documented to receive special education under an eligibility category of autism (range: 34% [Colorado]–76% [Maryland]) (Table 3). Other common special education eligibilities included “specific learning disabilities,” “speech and language impairments,” “other health impairments,” and “intellectual disabilities,” with these proportions also varying by site (Table 3).”

    The field of psychiatric epidemiology is fascinating because there are so many variables at play – “awareness” campaigns by patient groups, changes in medical education, advertising, cultural shifts and collective focus – not to mention shifting definitions in DSM and ICD iterations, and the general vicissitudes of history. I agree that for the same reasons it is interesting, it is a fairly frustrating.

    Personally I am skeptical of most large-scale epidemiological studies which treat diagnoses made by different clinicians of functional behavioral disease characteristics as though they are reliably intercoded. Not all studies are of that sort, but many tend to be.

    What is most remarkable, however, is the incredible culturo-historical traction these studies have, in spite of the fact that they do not often represent good science. They almost always get extensive press and end up cited in policy documents or brought up in legislative deliberations. For that reason, I don’t expect that there will be a dearth of them any time soon.


  3. I have a handicapped nearly 40-year-old son who doesn’t talk. Quite a few years ago he was tested at LPCH to see if he was autistic. At that time the result came back that Erik had “psychomotor retardation.” How that is distinguished from autism has never been explained. As to whether the greater availability of social services has increased the diagnoses of autism, I talked to Erik’s case worker. He thought there is an increase in diagnoses because of the increased attention to autism and the better services afforded with a diagnosis of autism.

    My problem is with the diagnosis of autism itself as being a purely behavioral or for that matter genetic phenomenon. First of all autism is ill-defined. In various studies the differences between genetic forms of autism (Rhett’s syndrome, fragile-x) and(Aspergers, Kanner’s)are almost never clearly defined. There also is no clear-cut distiction between autism and certain deficiency syndromes and toxicity-related phenomena (alcohol, lead, asenic, mercury etc.). Almost all the B-Vitamin deficiencies have mental and behavioral components. So do certain plant toxins. My experience has been that toxicology is a step-child of medicine. In addition, the doctors in my son’s past have had no or too little training in those areas (toxicology, nutrition, psychosis) to make reliable diagnoses.


  4. Obviously it’s better if one can be identified so he or she can get help. I have noticed however that it’s become “Trendy” to get disgnosed with such things, and each case should be evaluated properly.


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