The influence of comorbid oppositional defiant disorder on white matter microstructure in attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) are highly comor- bid disorders. ADHD has been associated with altered white matter (WM) microstructure, though the literature is incon- sistent, which may be due to differences in the in- or exclu- sion of participants with comorbid ODD. WM abnormalities in ODD are still poorly understood, and it is unclear whether comorbid ODD in ADHD may have confounded the current ADHD literature. Diffusion Tensor Imaging (DTI) was used to compare fractional anisotropy (FA) and mean diffusivity (MD) between ADHD patients with (n = 42) and without (n = 117) comorbid ODD. All participants were between 8–25 years and groups did not differ in mean age or gender. Follow-up analyses were conducted to examine the role of antisocial behaviour (conduct problems) on FA and MD val- ues in both groups. Comorbid ODD in ADHD was associated with lower FA in left frontotemporal WM, which appeared independent of ADHD symptoms. FA was negatively associ- ated with antisocial behaviour in ADHD + ODD, but not in ADHD-only. Comorbid ODD is associated with WM abnor- malities in individuals with ADHD, which appears to be independent of ADHD symptoms. Altered WM microstruc- ture in comorbid ODD may play a role in inconsistencies in the current DTI literature in ADHD. Altered development of these tracts may contribute to social-emotional and cog- nitive problems in children with oppositional and antisocial behaviour.