Neurocognitive Function in Attention-Deficit–Hyperactivity Disorder with and Without Comorbid Disruptive Behaviour Disorders

Objective: The aim of the present study was to examine the effect of comorbid oppositional defiant disorder (ODD) and conduct disorder (CD) on (i) symptom levels in attention-deficit–hyperactivity disorder (ADHD) and (ii) the relationship between neurocognitive impairment and ADHD symptom severity. Method: A total of 200 6–12-year-old children with DSM-IV ADHD, combined type (ADHD-CT) were identified in a specialist ADHD clinic in metropolitan Melbourne. From this initial group, 23 were identified with ADHD without ODD/CD (ADHD alone), 22 had ADHD and ODD and 20 had ADHD and CD. All the children were medication naïve. Twenty-five healthy control children were also recruited from local primary schools. The four groups did not differ in age, gender or full-scale IQ. A cross-sectional study of parent- and teacher-reported ADHD and externalizing symptoms, spatial span, spatial working memory, visuospatial memory, spatial recognition, spatial planning and behavioural inhibition was completed. Results: Parent-reported externalizing symptoms were higher in the ADHD + CD and ADHD + ODD groups compared to the ADHD alone group. There were no differences in neurocognitive function between children with ADHD-CT with and without ODD or CD. All the ADHD groups, however, performed worse than the healthy control group. Further, worse spatial span, spatial working memory and delayed matching to sample performance were associated with increased teacher-reported ADHD symptoms in the ADHD alone group. Also, worse spatial working memory performance was associated with increased teacher-reported ADHD symptoms in the ADHD + CD group. Conclusions: ADHD symptom severity is associated with the magnitude of impairment in executive functions in children with ADHD alone, but these relationships can be obscured by the presence of comorbid disruptive disorders. Children with ADHD + CD may demonstrate similar associations to children with ADHD alone, suggesting a similar underlying dysfunction. ADHD + ODD, however, may be better understood as a maladaptive response to the abnormal behaviours and neurocognitive functions in ADHD.