Autism spectrum disorder (ASD) and attention deficit hyperactivity disorder (ADHD) are neurodevelopmental disorders with onset of symptoms in early childhood. Research, practice and theoretical models suggest that these disorders frequently overlap and co-occur. For example, studies conducted in the US and Europe indicate that children with ASD in clinical settings present with comorbid (co-occurring) symptoms of ADHD with rates ranging between 37% and 85%. More severe externalizing, internalizing and social problems, as well as more impaired adaptive functioning, and more autistic traits and maladaptive behaviors have been reported in children with both ASD and ADHD than children identified with only ASD.
A study published in the journal Autism examined rates of parent-reported clinically significant symptoms of ADHD in a community sample of school-aged children (4-8 years) with ASD. The researchers hypothesized that children with ASD and comorbid ADHD would have lower cognitive functioning, greater delays in adaptive functioning, higher rates of internalizing problems (e.g., depression and anxiety), and more severe social impairment than children with only ASD when these groups were of similar age. Children were evaluated on measures of cognitive functioning, internalizing psychopathology, social functioning and autism mannerisms, and adaptive behavior.
Data analysis indicted significant between-group differences. Results revealed that scores were in the mild to moderately impaired range for the ASD-Only group and in the severely impaired range for the ASD+ADHD group on measures of social functioning and adaptive functioning, representing a continuum of impairment across groups. Children with ASD and ADHD also had lower cognitive functioning than the ASD-Only group. There were no group differences in parent ratings of symptoms of internalizing psychopathology (mood and anxiety disorders), with none of the groups demonstrating elevated rates of internalizing problems.
The overall results of the study indicate greater impairment in cognitive, social, and adaptive functioning for children with ASD and clinically significant ADHD symptoms in comparison with children identified with only ASD. These findings are consistent with other research reports of more severe social problems and maladaptive behaviors in children with co-occurring ASD and ADHD than children with only ASD. The results also have important implications for practitioners in health care, mental health, and educational contexts. It is imperative that practitioners recognize the high co-occurrence rates of these two disorders as well as the potential increased risk for social and adaptive impairment associated with comorbidity of ASD and ADHD. If clinically significant ADHD symptoms are identified, and social development does not appear to be responding to intervention, changes in the intervention program (e.g. intensity, strategies, and goals) may be required. It is also important to note that a significant change in the DSM-5 is removal of the DSM-IV-TR hierarchical rules prohibiting the concurrent diagnosis of ASD and ADHD. When the criteria are met for both disorders, both diagnoses are given. Thus, an assessment of ADHD characteristics should be included whenever inattention and/or impulsivity are indicated as presenting problems. More research is needed to further clarify the behavioral characteristics of children with co-occurring ASD and ADHD so that specialized treatments and interventions may be designed to improve outcomes and quality of life for this group of children.