Altered Brain Structure in Irritable Bowel Syndrome: Potential Contributions of Pre-Existing and Disease-Driven Factors

Background & Aims

Brain imaging studies have identified abnormal rectal-evoked responses and cortical thinning in patients with irritable bowel syndrome (IBS). However, it is not known whether these abnormalities are pre-existing or develop as result of long-term IBS. Therefore, we tested whether abnormal structural gray matter integrity in IBS correlates with individual disease symptoms, duration of the IBS, or the personality characteristic of pain catastrophizing.

Methods

Eleven IBS patients and 16 age-matched healthy subjects underwent structural magnetic resonance imaging. Voxel-based morphometry and cortical thickness analysis were used to identify abnormalities in subcortical and cortical regions, respectively, and their correlation to individual characteristics.

Results

The IBS group showed increased hypothalamic gray matter and cortical thinning in the anterior midcingulate cortex compared with controls, a strong negative correlation between dorsolateral prefrontal cortex thickness and pain catastrophizing, and a positive correlation between anterior insula thickness and pain duration. In the insula, there was cortical thinning in patients with short-term IBS, but long-term IBS pain was associated with a more normal insula thickness.

Conclusions

Our findings provide new insight into IBS and chronic pain through evidence for structural changes that could fit with functional abnormalities. We report that patients with IBS have increased hypothalamic gray matter, which may be related to the association among IBS, stress, and the hypothalamic-pituitary-adrenal axis. Furthermore, we have identified some supraspinal abnormalities that may be pre-existing and contribute to vulnerability, and others that may develop over time, possibly because of chronic abnormal inputs.

Keywords: Irritable Bowel Syndrome, Magnetic Resonance Imaging, Gray Matter, Pain

Abbreviations used in this paper: ACC, anterior cingulate cortex, aMCC, anterior midcingulate cortex, CTA, cortical thickness analysis, DLPFC, dorso-lateral prefrontal cortex, FDR, false discovery rate, fMRI, functional magnetic resonance imaging, IBS, irritable bowel syndrome, IC, insular cortex, MCC, midcingulate cortex, MRI, magnetic resonance imaging, PCS, pain catastrophizing scale, ROI, region of interest, S1, primary somatosensory cortex, S2, secondary somatosensory cortex, sMRI, structural magnetic resonance imaging, VBM, voxel-based morphometry