Corpus callosum abnormalities in medication-naïve adult patients with obsessive compulsive disorder.

Emerging evidence demonstrates widespread abnormalities involving white matter (WM) tracts connecting different cortical regions in obsessive-compulsive disorder (OCD). The corpus callosum (CC), the largest inter-hemispheric tract connecting the association cortices, has been shown to be affected in OCD. This study examines CC abnormalities in a large sample of medication-naïve OCD patients in comparison to matched healthy controls (HCs). We examined the mid-sagittal area of the CC in medication-naïve OCD patients (n=49) in comparison with age-, sex-, and handedness-matched HCs (n=38). Witelson's method was used to measure the sub-regions of the CC - namely, the genu, body, isthmus and splenium - with good inter-rater reliability. The area of the body of the CC and total CC area were significantly larger in OCD patients than in HCs after controlling for age, sex and intracranial area. The Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) compulsion score had a significant negative correlation with the areas of the isthmus and splenium of the CC in addition to the total CC area. The region-specific differences in the body of the CC and the region-specific association of severity score with posterior regions of the CC might be indicative of the involvement of additional areas like the dorsolateral prefrontal cortex, posterior parietal areas, occipital and association cortices in OCD that extend beyond the conventional orbito-fronto-striatal circuitry that is often posited to be involved in OCD.