S1084 Neuroimaging in Veterans With Irritable Bowel Syndrome (IBS): Analysis of the TRACTS (Translational Research Center for Traumatic Brain Injury and Stress Disorders) Longitudinal Prospective Cohort Study

Introduction: Irritable bowel syndrome (IBS) is a highly prevalent disorder of gut-brain interaction that is frequently comorbid with posttraumatic stress disorder (PTSD). Prior studies in non-veterans with IBS suggest that the brain areas involved are associated with pain or emotional processing and visceral sensation, but studies in the veteran population are lacking. This study aims to identify structural and functional brain changes in veterans with IBS, with or without PTSD, to gain insight into the pathophysiology of IBS. Methods: This study includes veterans enrolled in TRACTS, where participants undergo neuropsychiatric assessments and neuroimaging with magnetic resonance imaging (MRI). Participants screened in for IBS through review of the electronic health record based on Rome IV criteria. Exclusion criteria included inflammatory bowel conditions prior colonic surgery, and incomplete baseline data. Functional connectivity was modeled using a seed-based correlation approach focused on 8 components of the default mode network (DMN). Linear regression controlling for PTSD was used to estimate the effect of IBS on various brain regions. Data processing of major MRI sequences was used to measure morphometric properties of cortical and subcortical gray matter to obtain structural characteristics. Two-sample T tests were used to generate pairwise comparisons between groups. P < 0.05 was considered significant. Results: A total of 587 participants were enrolled including 50 IBS patients. When controlling for PTSD, functional MRI showed higher connectivity between the cingulate and the bitemporal components of the DMN associated with IBS. The DMN plays a key role in self-referential processing and emotional regulation. Structural data showed differences between participants with IBS and those with PTSD only. The structural findings were distinct from the areas noted to have increased functional connectivity in IBS. Conclusion: In this first structural and functional neuroimaging study in a large veteran population with IBS and PTSD, unique structural and functional brain imaging differences were identified in veterans with IBS compared with controls and those with PTSD. These results contrast with prior functional studies which showed reduced temporal lobe activation and resting-state functional connectivity in the DMN in IBS. This might suggest distinct brain pathomechanisms for IBS and PTSD in different brain regions which warrants exploration of their clinical phenotypes.