White Matter Microstructural Similarity and Diversity of Functional Constipation and Constipation-predominant Irritable Bowel Syndrome.

Background/aims: The Rome III criteria separated chronic constipation into functional constipation (FC) and constipation-predominant irritable bowel syndrome (IBS-C), but some researchers questioned the partitioning and treated both as distinct parts of a continuum. The study aims to explore the similarity and diversity of brain white matter between FC and IBS-C.

Methods: The voxel-wise analysis of the diffusion parameters was used to quantify the white matter changes of female brains in 18 FC patients and 20 IBS-C patients compared with a comparison group with 19 healthy controls by tract-based spatial statistics. The correlations between diffusive parameters and clinical symptoms were evaluated using a Pearson's correlation.

Results: In comparison to healthy controls, FC patients showed a decrease of fractional anisotropy (FA) and an increase of radial diffusivity (RD) in multiple major fibers encompassing the corpus callosum (CC, = 0.001 at peak), external capsule ( = 0.002 at peak), corona radiata (CR, = 0.001 at peak), and superior longitudinal fasciculus (SLF, = 0.002 at peak). In contrast, IBS-C patients showed FA and RD aberrations in the CC ( = 0.048 at peak). Moreover, the direct comparison between FC and IBS-C showed only RD differences in the CR and SLF. In addition, FA and RD in the CC were significantly associated with abdominal pain for all patients, whereas FA in CR ( = 0.016) and SLF ( = 0.040) were significantly associated with the length of time per attempt and incomplete evacuation separately for FC patients.

Conclusion: These results may improve our understanding of the pathophysiological mechanisms underlying different types of constipation.