Impact of ADHD symptoms on autism spectrum disorder symptom severity

Despite the official exclusion criteria for autism spectrum disorder (ASD) and attention deficit/hyperactivity disorder (ADHD) in the DSM-IV and ICD-10, patients with ASD often show ADHD symptoms. We aimed to examine the potential influence of ADHD symptoms on autistic psychopathology in a large sample of patients with ASD. We tested the hypothesis that patients with ASD and an additional ADHD (ASD+) would show a higher severity of autistic symptoms than those with ASD only (ASD-). We measured autistic symptoms using the autism diagnostic observation schedule (ADOS-G), the autism diagnostic interview (ADI-R), and the social responsiveness scale (SRS). To measure overall psychopathology and ADHD symptoms, we used the child behavior checklist (CBCL) and the ADHD rating scale (FBB-ADHS), respectively. Group differences between the ASD+ and the ASD- group (group division was conducted according to the results of the FBB-ADHS) were calculated using a univariate analysis of variance (ANOVA). The ASD+ group showed a greater severity of autistic symptoms than the ASD- group, measured by the SRS and the ADI-R. Especially in the social interaction subscale (ADI-R), a significantly higher symptom severity was found in the ASD+ group. No significant group differences were found regarding autistic symptoms measured by the ADOS-G. Patients with ASD and an additional ADHD expressed a stronger severity of autistic symptoms than patients with ASD only. According to our results, the possibility of a co-diagnosis of ADS and ADHD, as is being planned in the DSM-5, is in line with earlier studies, is highly reasonable, will simplify research, and have therapeutic implications.