Regional Cerebellar Volumetrics in Obsessive-Compulsive Disorder: An ENIGMA-OCD Study

Background: Although subtle differences in cortico-striato-thalamo-cortical circuit structure and function are critical to the current understanding of the neurocircuitry in obsessive-compulsive disorder (OCD), emerging evidence suggests that the cerebellum may also be involved. However, much of this evidence comes from studies with small samples and notable methodological heterogeneity. Methods: We conducted a mega-analysis of individual-participant data on cerebellar subregional volumes, comparing individuals with OCD and healthy controls (HCs) from the ENIGMA-OCD Working Group. Three-dimensional T1-weighted volumetric structural brain magnetic resonance imaging (MRI) scans from 1954 individuals with OCD and 2091 HCs across 22 sites (40 datasets) were processed using the ACAPULCO (Automatic Cerebellum Anatomical parcellation using U-Net Locally Constrained Optimization) pipeline to extract cerebellar parcellations. We harmonized the volume measures across sites using the ComBat algorithm. Multiple linear regression models were fitted to estimate group differences separately within the pediatric (<12 years), adolescent (12–17 years), and adult (from 18 years) samples, adjusting for age, gender, and intracranial volume. Results: In adults with OCD (vs. HCs), we found significantly smaller volumes of the corpus medullare (d = −0.093, false discovery rate (FDR)–corrected p = .036), left VIIb (d = −0.085, pFDR = .039) and right VIIb (d = −0.091, pFDR = .036). None of the comparisons between children or adolescents with OCD versus HCs remained statistically significant after FDR correction. In all 3 age groups, cerebellar (subregional) volumes were significantly moderated by medication status. Conclusions: We report novel findings implicating specific cerebellar subregions across developmental stages of OCD and the key impact of medication status. Additional research on the functional significance of these findings may offer new translational leads.