01/23/2012 01:56 pm ET

New Study Sheds Light On Why Autism Diagnosis Can Be So Difficult

Medical diagnoses are rarely clear-cut, and that may be particularly true among children with autism.

A new study finds that children with autism spectrum disorders are more likely to also have other developmental or psychiatric conditions -- highlighting one possible reason why many have changing diagnoses as they get older.

The study, published Monday in the journal Pediatrics, relied on data from more than 1,300 children from the 2007 National Survey of Children's Health, broken into three age groups -- ages 3 to 5, 6 to 11 and 12 to 17. Based on parental reporting, those kids were further broken into two categories: those with a current diagnosis of autism, and those who had been diagnosed in the past, but no longer met the criteria for an autism spectrum disorder (ASD).

According to the study, children ages 3 to 5 with a current diagnosis of autism were 11 times more likely to have a learning disability and were also more likely to have developmental delays than those with a past diagnosis.

Children ages 6 to 11 with a current diagnosis had higher rates of past speech problems as well as anxiety issues in the present than those who had a past diagnosis, while adolescents with a current autism diagnosis had higher rates of speech problems and were 10 times more likely to have epilepsy than those who no longer met criteria for the developmental disorder.

Overall, children with an ASD were more likely to have two or more co-occuring conditions than those with a past diagnosis.

"This study is helpful as the authors try to predict which children on the spectrum will improve. Rather than determining future outcomes based on the severity of ASD symptoms or whether the child participated in a specific treatment, the authors instead use the presence of co-occurring disorders as a tool to predict whether an ASD diagnosis will persist," said Dr. Steven Meyers, a professor of psychology at Roosevelt University and a Chicago-based clinical psychologist who was not associated with the research.

"Their findings suggest that health care providers should learn whether children on the spectrum also have a learning disability, a speech problem, or a hearing problem to help them judge whether symptoms of autism will improve as time progresses," he continued.

But the new study does not explain why certain coexisting conditions may be linked with changes in autism diagnoses. Diagnostic inaccuracies or shifts in diagnostic determination might be at play, as the symptoms of developmental and psychiatric conditions often overlap.

The authors explain that as children age, it may become clear to doctors that what they once thought was a speech or hearing problem may in fact be a symptom of autism; conversely, children diagnosed with an ASD in the past may simply have one of the common co-occurring conditions.

As researchers work to disentangle such issues from other possible underlying mechanisms, the study's authors say their research serves as a powerful reminder to parents that diagnosis can be tricky and that they should consider the possibility that children can have multiple conditions simultaneously in order to identify the best intervention as quickly as possible.

"It's important when parents go to talk to a clinician that they request a full evaluation on possible co-existing conditions, in addition to the core symptoms of autism," study co-author Li-Ching Lee, Ph.D., a research scientist with the Johns Hopkins Bloomberg School of Public Health said. "To avoid possible mis-diagnosis, you want to ask your doctor to go through and test for many things."