Association of increased grey matter with obsession and anhedonia in adolescent obsessive-compulsive disorder

Adolescent obsessive-compulsive disorder (OCD) is a severe psychiatric condition, but its neurodevelopmental origin remains understudied. Structural neuroimaging findings in adolescents are inconsistent and rarely linked to specific symptom dimensions, particularly anhedonia.

We conducted voxel-based morphometry to investigate grey matter volume (GMV) in 38 adolescents with OCD and 31 healthy controls (HC), supplemented by exploratory surface-based morphometry and medication-based subgroup analyses. Clinical assessments included the Children's Yale-Brown Obsessive Compulsive Scale and the Children's Depression Inventory. We conducted between-group comparisons, correlation analyses with obsessive severity, and mediation analysis to test the role of the right putamen in anhedonia-obsession relationship.

Adolescents with OCD exhibited significantly increased GMV in limbic, paralimbic, and subcortical regions, including the left hippocampus/amygdala, bilateral insula, and right putamen, along with increased sulcal depth in the left precentral gyrus. GMV exhibited a graded decrease across the unmedicated OCD, medicated OCD, and HC groups. Importantly, right insular and putamen GMV were positively correlated with obsessive symptoms. Mediation analysis revealed that putamen GMV partially mediated the relationship between anhedonia and obsessive symptoms (indirect effect = 0.199, 95% CI: 0.067-0.380).

This study identifies a distinct pattern of increased GMV in adolescent OCD, implicating the regions involved in emotional processing, salience detection, and habit formation. The correlation between right insula/putamen structure and obsessive symptoms, and the mediation role of the putamen between anhedonia and obsession together suggested a novel neuroanatomical model linking reward processing deficits to core OCD symptomatology. Our findings highlight potential targets for future mechanism-based interventions.