Posttraumatic stress symptoms in chronic pain: impacts on brain morphology

Background Posttraumatic stress symptoms (PTSS) are commonly experienced by people with chronic pain. Although PTSS and chronic pain are associated with similar effects on brain morphology, the present study aimed to clarify the relationship between chronic pain and PTSS on the brain. Methods Fifty-two people with chronic pain and 38 pain-free healthy controls (HC) underwent T1-weighted magnetic resonance imaging. Severity of PTSS was measured using the civilian version of the posttraumatic stress disorder checklist (PCL-C). A series of multiple linear regressions determined the main effects of group, PTSS severity (PCL-C total score and symptom-specific scores) and their interaction on grey matter volume of selected regions-of-interest. Results The interaction term was significantly associated with variations in grey matter volume in the left and right putamen, the left middle cingulate cortex (MCC) and the right posterior insula. Results showed significantly smaller left and right putamen when reporting higher PTSS levels, and significantly larger left MCC and right posterior insula at lower PTSS levels in people with chronic pain compared to HCs. In addition, increasing PTSS severity was significantly associated with larger left and right putamen in HCs, and significantly associated with smaller left MCC and right posterior insula, in people with chronic pain. Conclusions Severity of PTSS moderated chronic pain-related grey matter alterations. More severe PTSS, especially avoidance, was associated with smaller left MCC, a core region of the “pain matrix”. The MCC is strongly linked with the somatosensory network, and critical for empathy, especially toward pain-related stimuli. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by a project grant from the National Health and Medical Research Council of Australia (ID1084240) and a Rebecca Cooper Fellowship from the Rebecca L. Cooper Medical Research Foundation awarded to S.M.G. N.N.-N. was supported by the Australian Government Research Training Program Scholarship (administered by the University of New South Wales) and a supplementary scholarship, and PhD Pearl Award administered by Neuroscience Research Australia. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Human Research Ethics committees of the University of New South Wales (HC15206), the University of Sydney (HREC06287) and Northern Sydney Local Health District (1102-066M) gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors