Neuropsychological Characteristics of Individuals with Mixed High Functioning ASD and ADHD

Background: Clinical heterogeneity is a well-established characteristic of ASD. It is estimated that 75% of individuals with ASD present associated medical conditions, genetic syndromes, mental health or developmental disorders (Ghaziuddin, 2008). In addition to the social communication impairment and the presence of restricted and repetitive behavior, a large portion of individuals with ASD presents symptoms of ADHD. While the comorbidity of ASD and ADHD is well known in the clinical realm, relatively little research has examined the neuropsychological profiles of children with mixed ASD and ADHD.

Objectives: To examine the neuropsychological characteristics of individuals with ASD + ADHD and those with ASD only.

Methods: 57 individuals with high functioning ASD (FSIQ > 70) were enrolled in the study. The sample consisted of 22 children with ASD and 25 children with ASD + ADHD (age 7 to 13). The battery administered to all participants comprised the Wechsler Scales of Intelligence, the Child Behavior Checklist (CBCL), the “Reading the Mind in the Eyes” (Baron-Cohen, 2001) used to evaluate empathy, the Purdue Pegboard Test used to evaluate manual dexterity, and the Tower of London Test used to evaluate planning.

Results: The groups did not differ in FSIQ, VIQ, or PIQ. ADHD symptoms (t = - 2.19; p = .03) and anxiety symptoms (t = -1.95; p = .05), as measured by the CBCL, were higher in the group of children with ASD + ADHD in comparison to the group with ASD only. Moreover, after controlling for FSIQ, children with ASD + ADHD showed significantly lower scores, in comparison to children with ASD only, in Working Memory (F = 4.52; p = .04) and marginally significantly lower scores in the “Reading the Mind in the Eyes” Test (3.48; p = .70). There were not significant differences in the Purdue Pegboard Test or in the Tower of London Test between the groups.

Conclusions: Our results showed significant differences in the neuropsychological characteristics of children with ASD + ADHD in comparison to those with ASD only. This suggests that having ADHD brings further challenges to individuals with ASD. Our findings may have implications for clinical assessment as well as intervention.