Widespread alterations of white matter integrity in medication-free obsessive-compulsive disorder

Previous studies have highlighted alterations of white matter (WM) integrity underlying mechanisms of obsessive-compulsive disorder (OCD). However, whole-brain WM abnormalities in OCD at the tract-level still remain largely unknown. In current study, we evaluated the integrity of 42 WM tracts in individuals with OCD using the novel tractography toolbox, TRActs Constrained by UnderLying Anatomy (TRACULA), and investigated the grey matter changes linked to the white matter alterations. Furthermore, we investigated the association of diffusion measures with clinical symptom severity. DTI and T1-weighted image data were collected from 54 medication-free OCD patients and 39 age- and sex-matched healthy controls (HCs). TRACULA was used to reconstruct 42 WM tracts and produce tract volume, fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) of each tract, and grey matter measures were extracted from T1-weighted images. Group comparisons of these measures were evaluated with analysis of covariance. Comparing to HCs, OCD patients showed widespread decreased FA, including rostrum of the corpus callosum, uncinate fasciculus, frontal aslant tract, inferior longitudinal fasciculus, acoustic radiation and optic radiation. Additionally, we found grey matter changes linking to the detected white matter changes, including abnormalities in the medial orbital frontal cortex, superior frontal gyrus, pars opercularis, precentral gyrus, postcentral gyrus, lingual gyrus, and Heschl's Gyrus. Our results demonstrated that OCD had structural disconnection not only within the traditional frontal-limbic networks but also extended to the visual and auditory systems.