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Trends in ASD Co-Occurring Diagnoses in the Autism and Developmental Disabilities Monitoring Network
A recent report from the Autism and Developmental Disabilities Monitoring (ADDM) Network reported that 83% of 8-year-olds with an autism spectrum disorder (ASD) had at least one co-occurring developmental, neurologic, or psychiatric diagnosis (CD). Estimated prevalence of ASDs has significantly increased from 2002 to 2008. Little is known regarding the frequency of CDs among children with ASDs over time and whether specific CDs are increasing in relation to the increase in estimated prevalence of ASDs.
Objectives:
To examine the prevalence of CDs among children with an ASD and whether prevalence of CDs has changed.
Methods:
The ADDM Network is a biennial multiple source population-based surveillance system for ASDs and other developmental disabilities in 8-year-old children. Case identification is based on reviews of special education and health records. This study examined data from the 2002, 2006, and 2008 surveillance years. The sample was limited to ADDM sites for which >85% of children with ASDs had information on cognitive ability recorded. Altogether the sample included 4,051 children with ASDs identified at four sites. For each surveillance year, mean number of CDs was calculated and 95% confidence intervals (CI) were estimated using the Poisson distribution. To evaluate trends, extended Mantel-Haenszel tests were conducted, adjusting for site and whether the child’s ASDs classification was based on review of education records only, health records only, or both. Tests were run for two variable types: 1) a categorical grouping of diagnosis type (developmental diagnoses, psychiatric diagnoses, neurological diagnoses, and possible causative medical diagnoses [such as birth defects or genetic disorders]); and 2) individual diagnoses subsumed within these 4 types.
Results:
In this sample of children with ASDs, the mean number of CDs increased significantly from 2.09 in 2002 (CI 1.99-2.19) to 2.32 in in 2008 (CI: 2.25-2.39) (p<0.001). In 2008 65.4% of children had one or more developmental CDs, 5.7% had one or more psychiatric CDs, 4% had one or more neurologic CDs, and 0.36% had one or more possible causative CDs. Thirty-six distinct CDs were identified: 13 developmental diagnoses, 13 psychiatric diagnoses, 6 neurological diagnoses, and 4 possible causative medical diagnoses. Of the 36 specific diagnoses, “developmental delay”, a general diagnosis subsumed within the broader developmental diagnoses category was most frequent. Further, it increased from 56% in 2002 to 65% in 2008 (p<0.001). There were also significant trends in two other developmental diagnoses; language disorder increased and intellectual disability decreased. None of the conditions included in the psychiatric, neurologic, or possibly causal medical diagnoses categories changed from 2002-2008.
Conclusions:
CDs were prevalent in our population-based sample, which could complicate the identification and diagnosis of children with ASDs. Co-occurring developmental diagnoses were especially prominent and one of these, developmental delay, has increased significantly since 2002. These results highlight the need for clinicians to be aware of the high prevalence of CDs in children with ASDs. CDs likely impact the observed phenotypic heterogeneity of ASDs and need to be considered in developing treatment strategies for children with ASDs.