Left insular cortical thinning differentiates the inattentive and combined subtype of adult attention-deficit/hyperactivity disorder

Background: Neuroimaging studies in attention-deficit/hyperactivity disorder (ADHD) demonstrated decreased global gray matter volume. In terms of surface parameters, most investigations focused on cortical thickness with a multi-center MEGA-analysis indicating cortical thinning in children, but not in adults with ADHD. In this single-scanner study, for the first time in adult ADHD, we additionally examined metrics beyond cortical thickness and surface area, namely sulcal depth and fractal dimension as measures of cortical alteration and complexity. Unlike most previous studies, ADHD subtypes were considered. Methods: As part of the Comparison of Methylphenidate and Psychotherapy in Adult ADHD Study (COMPAS), surface parameters were analyzed in 131 adults with ADHD (66 combined, 60 inattentive and 5 hyperactive/ impulsive subtype) and 95 healthy controls with the Computational Anatomy Toolbox (CAT12) using Statistical Parametric Mapping Software (SPM). Results: Neither at the vertex-nor at the region of interest-level, the ADHD and control group differed signifi-cantly with regard to cortical thickness, gyrification index, sulcal depth or fractal dimension. Contrasting the combined and the inattentive subtype, patients of the combined subtype showed a significant thinning of the left anterior insular cortex. Thinner left pars opercularis cortical thickness was associated with symptoms of hy-peractivity/restlessness. Conclusions: Resembling previous findings of a correlation of the left anterior insular gray matter volume with oppositional symptoms in adolescents with ADHD, we detected left anterior insular cortical thinning in the ADHD combined subtype. Left insular cortical thickness could represent a potential marker to distinguish the predominantly inattentive and the combined ADHD subtype in adulthood.

Automated summary

This study explored neuroimaging in adult patients with attention-deficit/hyperactivity disorder (ADHD). The analysis of surface parameters did not reveal significant differences in cortical thickness, gyrification index, sulcal depth, or fractal dimension between ADHD patients and healthy controls. However, when comparing different subtypes of ADHD, significant thinning of the left anterior insular cortex was observed in the combined subtype.