Adult OCD patients with an adult illness onset (N=775) compared to controls (N=1436) showed thinner cortices in left and right hemisphere overall. Regionally, we observed thinner cortices in frontal and temporal regions of adult-onset patients (Cohen’s d between −0.11 and −0.16; Supplementary Table S21a and Figure S15). We also found lower surface area of the left transverse temporal cortex (Cohen’s d −0.17) and the left pars opercularis (Cohen’s d −0.14) in adult OCD patients with an adult illness onset (Supplementary Table S22a and Figure S16). We did not detect significant differences in cortical thickness or surface area in adult OCD patients with a childhood illness onset (N=646) compared to controls or when comparing adult-onset and childhood-onset patients directly (Supplementary Tables S21b–c and Supplementary Tables S22b–c).
