Shared and Unique Structural Covariance Connectivity in Comorbidity of Obsessive‐Compulsive Disorder and Major Depressive Disorder

Background The comorbidity of obsessive–compulsive disorder (OCD) and major depressive disorder (MDD) is a prevalent clinical phenomenon, which is associated with greater symptom severity, suicide risk, and poorer treatment outcomes. However, the neural basis of this comorbidity remains unclear. The aim of this study was to investigate the common and unique neural basis of comorbidity compared with OCD and MDD alone. Methods A total of 67 patients with comorbid OCD and MDD, 89 patients with OCD alone, 94 patients with MDD alone, and 94 healthy controls (HCs) completed the acquisition of T1‐weighted structural images and were included in the present study. The gray matter volume of each brain region in the AAL116 atlas was calculated, based on which the structural covariance between each pair of brain regions was measured. One‐way ANCOVA were performed to explore the structural covariance differences among the four groups. Results Compared with HC, patients with comorbidity and patients with OCD or MDD alone showed some common altered structural connections ( p < 0.05, false discovery rate [FDR] correction). Patients with comorbidity showed unique altered correlation strength of gray matter volume between left cerebelum_crus1 and left orbital frontal cortex (OFC), left Rolandic operculum, right rectus, right parahippocampal gyrus, left and right fusiform gyrus (FG), left Heschl gyrus, left and right superior temporal gyrus (STG), and left cerebelum_crus2; these 10 connections were also significantly different when comparing comorbidity with OCD and MDD separately ( p < 0.05, FDR correction). Conclusions Compared with OCD or MDD alone, comorbidity showed both common and unique altered structural covariant connections of gray matter structure. The unique structural connections observed in comorbidity were concentrated between the cerebellum and other brain regions. These findings highlight the crucial role of the cerebellum in the neural basis of comorbid OCD and MDD.