Children currently diagnosed with an autism spectrum disorder are more likely to have coexisting psychiatric or neurodevelopmental conditions than are children with a past but not current diagnosis, and these conditions might lead to a change in ASD diagnosis, suggest the findings of a cross-sectional study in the February issue of Pediatrics.

An estimated 1% of 8-year-old children (typically the peak age of prevalence) have an ASD, such as autistic disorder; pervasive developmental disorder, not otherwise specified (PDD-NOS); or Asperger’s syndrome, according to the Centers for Disease Control and Prevention. Co-occurring conditions often include attention-deficit/hyperactivity disorder, learning disability, depression, anxiety, and seizures. Also, more than 10% of children diagnosed with an ASD at age 2 years no longer have the diagnosis by age 9 years.

To provide an appropriate diagnosis and opportunities for early intervention, clinicians must be able to differentiate between the core features of an ASD and any coexisting conditions.

Using cross-sectional data from the National Survey of Children’s Health 2007 (NSCH), Heather A. Close, of the Center for Autism and Developmental Disabilities Epidemiology at Johns Hopkins University, Baltimore, and her colleagues examined the relationship between co-occurring conditions and changes in diagnosis of an ASD (Pediatrics 2012;129:305-16 [doi:10.1542/peds.2011-1217]). This study consisted of 1,366 children from the NSCH with a parent-reported current or a past but not current (PBNC) diagnosis of an ASD.

The study authors found that the type of co-occurring conditions varied by age. For example, 3- to 5-year-old children currently diagnosed with an ASD were 11 times more likely to have a moderate or severe learning disability and 9 times more likely to have a moderate or severe developmental delay than children with a PBNC diagnosis. They were nearly 5 times more likely to have two or more current co-occurring conditions than children with a PBNC diagnosis of an ASD.

Meanwhile, children aged 6-11 years with a current ASD diagnosis were almost 4 times more likely to have had a past speech problem and 3.5 times more likely to have current moderate or severe anxiety than children with a PBNC diagnosis. And, they were more than 3 times as likely to have two or more current co-occurring conditions as those with a PBNC diagnosis.

Finally, adolescents aged 12-17 years with a current ASD diagnosis were almost 4 times more likely to have moderate or severe speech problems and 10 times more likely to have current mild seizures or epilepsy than children with a PBNC diagnosis of ASD.

Children and adolescents with a current ASD diagnosis were more likely to have two or more co-occurring conditions than those with a PBNC diagnosis.

The study results suggest that some co-occurring conditions might, in part, lead to a change in an ASD diagnosis, although the underlying mechanisms for this change are unclear. In this study, the researchers focused on the possible impact that neurodevelopmental and psychiatric conditions could have on the continuation of ASD diagnosis by comparing groups who currently have an ASD diagnosis to groups with a PBNC diagnosis.

"Our results are in line with the few studies that have researched differences between current or past ASD diagnoses in the context of co-occurring conditions," Ms. Close and her colleagues wrote.

Children with ASDs have impaired communication, including delays in speech and acquisition of language, or delays in age-appropriate social skills. With increasing age, these symptoms appear more consistent with ASD than with what might have been considered a speech or hearing problem or a nonspecific developmental delay.

"This can also be true in the opposite direction, in which a child might have been diagnosed with an ASD because of the presence of common ASD co-occurring conditions or diagnoses and then was later reclassified as not having an ASD," the researchers said.

Possible reasons for reclassifying children previously diagnosed with an ASD include developmental improvements as the child ages, such as in IQ or adaptive social abilities, or a child no longer meeting the diagnostic criteria as a result of early intervention. "Improvements leading to a loss of an ASD diagnosis also occur more commonly in children diagnosed at an early age with PDD-NOS rather than with autistic disorder," the researchers said.

The limitations of this study included the fact that information was based on parent-reported diagnoses obtained through one telephone interview; the different outcomes among children and adolescents with autism, Asperger’s syndrome, and PDD-NOS; the small sample size for some variables of interest; and a lack of information on individual interventions for each study. Also, the study investigated children with a current or previous ASD diagnosis but did not specifically look at the change from never having a diagnosis to having a diagnosis.

A prospective, longitudinal, population-based retrospective study of adults that asks similar questions could offer a detailed profile of the ages at which an ASD diagnosis changes, as well as co-occurring conditions and interventions, the researchers said.

The authors had no financial relationships to disclose.

Coexisting Conditions May Explain Change in Autism Diagnosis