Identifying Autistic-Like Symptoms in Children with ADHD: A Comparative Study Using ADOS-2

Recent literature has focused attention on the presence of autistic-like symptoms in children with Attention Deficit/Hyperactivity Disorder (ADHD), who often exhibit social difficulties, posing challenges for a distinct clinical diagnosis. The current study aimed to identify the specific pattern of autistic symptoms in subjects with ADHD or Autistic Spectrum Disorder (ASD), examining similarities or differences at both the domain and individual item levels. In this study, we enrolled 43 school-age children divided into the following: the ADHD group (n=25) consisted of children initially referred for ASD symptoms but subsequently clinically diagnosed with ADHD, and the ASD group consisted of 18 children with ASD. We used the Autism Diagnostic Observation Schedule, 2nd edition (ADOS-2), to examine relative differences in the presence of symptoms such as deficits in communication and social interaction, and restricted and repetitive behaviors in these two groups. Comparison between groups was conducted to explore differences in IQ, age, ADOS-2 domains, and externalizing and internalizing problems among the groups. We found significant differences between the groups when comparing summary scores of ADOS-2 domains (Social Affect, Restricted and Repetitive Behavior, and Total Score). Interestingly, at the individual item level, the ADHD group exhibited a similar level of atypical behaviors compared to the ASD group in two items related to the social-communication area: "Pointing" and "Gestures". Additionally, the frequencies of "Stereotyped/idiosyncratic words or phrases", "Mannerisms", and "Repetitive interests and behaviors" also showed similarities between groups. These findings indicate the importance of exploring and developing potential transdiagnostic domains that could be targeted for treatments specifically designed for children with ADHD.