Rise in autism cases may be over-estimated

By Will Boggs, MD

NEW YORK (Reuters Health) - Changes in the criteria for diagnosing autism may account -- at least in part -- for the marked rise in the number of new cases in the last few decades, the results of a small study suggest.

"The dramatic increase in rates of diagnosis of autism does not necessarily mean there is an epidemic of new cases," Dr. Dorothy V. M. Bishop from the University of Oxford, UK, told Reuters Health. "A large part of the increase could be due to an autism diagnosis being given to children who would previously be identified as having other conditions."

As described in the journal Developmental Medicine and Child Neurology, Bishop and colleagues used follow-up data on 38 adults diagnosed with developmental language disorder 5 to 25 years earlier to test their hypothesis that some would currently be diagnosed with autism.

The authors found that, in fact, this was the case, suggesting that if the diagnostic criteria had held steady over the last few decades, it is possible that a dramatic rise in cases would not have been seen.

Still, because the study was small, "we are not able to estimate just how much of the increase (in autism rates) is due to such diagnostic reassignment," Bishop said.

SOURCE: Developmental Medicine and Child Neurology, April 2008.