Posttraumatic stress-related white matter microstructure alterations and chronic pain

Background. Posttraumatic stress symptoms (PTSS) are commonly experienced in people with chronic pain. Reduced white matter microstructural integrity in the uncinate fasciculus and the cingulum has been reported similarly in chronic pain and PTSD studies separately. However, the relationship between chronic pain, PTSS and white matter integrity remains unclear. Methods. Thirty-six subjects with and 20 without chronic pain (controls) underwent diffusion weighted imaging and completed the civilian version of the Posttraumatic stress Disorder CheckList (PCL-C). Average fractional anisotropy (FA) and mean diffusivity (MD) values were extracted from three regions-of-interest (uncinate fasciculus, cingulate and hippocampal portions of the cingulum). A series of multiple linear regressions determined the main effects of Group, PTSS severity (PCL-C total score) and their interactions on each ROI separately. Results. The group-by-PTSS interaction was significantly associated with variations of uncinate fasciculus FA. Moderation analysis indicated that increasing PTSS severity was significantly associated with reduced uncinate fasciculus FA in the control group, but not in chronic pain group. No other significant association was found for any other ROI FA values, and there was no significant association with MD values. Conclusions. Consistent with previous studies, increasing PTSS levels were associated with reduced FA of the uncinate fasciculus in controls, but not in people with chronic pain. This suggests that different mechanisms may be at play in chronic pain, including the interplay with other psychopathological problems, such as depression and anxiety. Future larger studies of more homogeneous chronic pain conditions are warranted.