Autism and ADHD: Overlapping and discriminating symptoms

Children with ADHD and autism have some similar features, complicating a differential diagnosis. The purpose of our study was to determine the degree to which core ADHD and autistic symptoms overlap in and discriminate between children 2–16 years of age with autism and ADHD. Our study demonstrated that 847 children with autism were easily distinguished from 158 children with ADHD. All children with autism had 15 or more of the 30 Checklist for Autism Spectrum Disorder symptoms (mean 22), and none of the children with ADHD did (mean 4). Three of the symptoms were present only in children with autism. Almost all 30 symptoms were found in over half of the children with autism, whereas none were present in the majority of children with ADHD-Inattentive type (ADHD-I) or in children with ADHD-Combined type (ADHD-C) without comorbid oppositional-defiant disorder. In contrast, ADHD symptoms were common in autism. Children with low and high functioning autism and ADHD-C did not differ on maternal ratings of attention deficit, impulsivity, and hyperactivity. For children with normal intelligence, nonsignificant differences were found between children with autism, ADHD-C, and ADHD-I on neuropsychological tests including measures of attention, working memory, processing speed, and graphomotor skills.

► Our study demonstrates that children with autism can easily be distinguished from children with ADHD based on their symptom profiles.
► The core symptoms of ADHD (attention deficit, impulsivity, and hyperactivity) are part of autism, and autism and ADHD have similar underlying neuropsychological deficits.
► Autistic symptoms are not common in ADHD.
► Because of the high frequency of ADHD symptoms in autism, children with autism may initially be misdiagnosed with ADHD.