Abnormal fractional anisotropy and correlation to symptom measures in irritable bowel syndrome

Irritable Bowel Syndrome (IBS) is a common gastrointestinal disorder characterized by abdominal pain and disturbed bowel habits, with poor relation to physical gastrointestinal pathology. Recent functional and structural brain imaging studies in IBS patients have found abnormal conical responses to rectal distension and reduced gray matter areas within key regions associated with pain processing. This thesis sought to use diffusion tensor imaging (DTI) to assess the hypothesis that the structural integrity of white matter (WM) within the pain network is compromised in IBS patients, and also to test the impact of individual disease characteristics and personality factors. Magnetic resonance imaging (MM) was used to obtain DTI images from 10 IBS patients and 16 age- and sex-matched healthy controls. Participants completed questionnaires to assess neuroticism (NAPE I) and pain catastrophizing (PCS), and patients were also interviewed to attain their symptom history (specifically, ratings of pain severity, pain unpleasantness, and duration since symptom onset). Tract-based spatial statistics (TBSS) was implemented in FSL 4.1 to generate a white matter skeleton, from which mean fractional anisotropy (FA) values were extracted for regions of interest: Si, medial and lateral thalamic nuclei (MD, VPL), anterior-mid cingulum (maC), anterior and posterior insula (aIC, pIC), and fornix. Student's t-test and linear regression (p < 0.05) revealed that patients have higher mean FA in the fornix and WM adjacent to the right pIC, and that mean FA in bilateral aIC correlated positively with pain severity in patients. Pain severity also correlated positively to mean FA of WM traversing the right VPL, whereas pain unpleasantness only correlated positively to mean FA of WM adjacent to the left aIC. Duration since symptom onset correlated positively to mean FA in the external capsule adjacent to the left pIC. PCS scores correlated positively to mean FA in the external capsule adjacent to the left aIC and pIC in controls but not patients, and also correlated negatively to mean FA in the maC in patients but not controls. Finally, neuroticism correlated positively with mean FA in the left MD in patients but not controls. These findings primarily implicate the integrity of the fornix and insular white matter in IBS status and symptoms, and add to evidence suggesting that dysregulation of brain-gut communication via the neuroendocrine pathway or via abnormal visceral sensory and homeostatic input may be central to IBS pathology.