Altered brain morphology in boys with attention-deficit/hyperactivity disorder with and without comorbid conduct disorder/oppositional defiant disorder

About 50% of ADHD patients suffer from comorbidity with oppositional defiant disorder/conduct disorder (ODD/CD). Most previous studies on structural morphology did not differentiate between pure ADHD (ADHD-only) and ADHD with comorbid ODD/CD (ADHD+ODD/CD) and only focused on specific measures (e.g. volumetric differences), leading to inconsistent results. Therefore, we aimed to investigate the structural profile of ADHD-only versus ADHD+ODD/CD spanning different indices, i.e. subcortical and cortical volume, cortical thickness, and surface area. We aimed to disentangle disorder-specific etiological contributions regarding structural brain alterations and expected similar and differential alterations between the patient groups. We acquired structural images from an adolescent sample range (11 to 17 years) matched with regard to age, pubertal status, and IQ - including 36 boys with ADHD-only, 26 boys with ADHD+ODD/CD, and 30 typically developing boys (TD). We analyzed subcortical and cortical volume, cortical thickness, and surface area with FreeSurfer. We found reductions in total gray matter and right cerebellar volume as well as total surface area for both patient groups. For the left cerebellar volume ADHD+ODD/CD, but not ADHD only differed from TD. Boys with ADHD+ODD/CD had a thicker cortex than the other groups in a right rostral middle frontal cluster, which was related to stronger ODD/CD symptoms, even when controlling for ADHD symptoms. No group differences in local cortical volume or surface area emerged. Overall, we found similarities but also differences in brain morphology between the two related disorders. Patients with a "double burden" seem to be even more affected than patients with pure ADHD.