Structural Brain Abnormalities of Attention-Deficit/Hyperactivity Disorder with Oppositional Defiant Disorder

Background: Attention-Deficit/Hyperactivity-Disorder (ADHD) is associated with structural abnormalities in total gray matter, basal ganglia and cerebellum. Findings of structural abnormalities in frontal and temporal lobes, amygdala, and insula are less consistent. Remarkably, the impact of comorbid Oppositional Defiant Disorder (ODD) (comorbidity rates up to 60%) on these neuroanatomical differences is scarcely studied, while ODD (in combination with Conduct Disorder (CD)) has been associated with structural abnormalities of the frontal lobe, amygdala, and insula. The aim of this study was to investigate the effect of comorbid ODD on cerebral volume and cortical thickness in ADHD. Methods: Three groups (mean age 16 year, SD=3.5, range 7-29) were studied on volumetric and cortical thickness characteristics using structural magnetic resonance imaging (Surface-Based Morphometry): ADHD+ODD (n=67), ADHD-only (n=243), and controls (n=233). Analyses included moderators age, gender, IQ, scan-site. Results: ADHD+ODD and ADHD-only showed volumetric reductions in total gray matter and (mainly) frontal brain areas. Stepwise volumetric reductions (ADHD+ODD<ADHD-only<controls) were found for mainly frontal regions, and ADHD+ODD was uniquely associated with reductions in several structures (e.g. the precuneus). In general, findings remained significant after accounting for ADHD symptom-severity. There were no group differences in cortical thickness. Exploratory voxel-wise analyses showed no group differences. Conclusions: ADHD+ODD and ADHD-only were associated with volumetric reductions in brain areas crucial for attention, (working) memory and decision-making. Volumetric reductions of frontal lobes were largest in the ADHD+ODD group, possibly underlying observed larger impairments in neurocognitive functions. Previously reported striatal abnormalities in ADHD may be due to comorbid CD, rather than ODD