Age-Accelerated Reduction in Cortical Surface Area in United States Service Members and Veterans with Mild Traumatic Brain Injury and Post-Traumatic Stress Disorder.

Despite the prevalence of combat-related mild traumatic brain injury (mTBI) and relatively high incidence of concurrent post-traumatic stress disorder (PTSD), the joint effect of these conditions on the brain is not well understood. Further, few studies in the mTBI or PTSD populations focus on cortical surface area measures, despite known disruptions to cytoarchitecture of the cortex. This study examines the effects of comorbid mTBI and PTSD on age-related surface area changes across the cortex, as compared with a group with mTBI only. While a direct comparison of PTSD versus non-PTSD groups showed little difference on surface area measures, several regions showed a decline in surface area, with increasing age and a significant PTSD-by-age interaction effect, indicating an age-dependent decrease in surface area in those with both mTBI and PTSD. The findings suggest an apparent age-accelerated shrinking of the cortical surface area in some regions when mTBI and PTSD are present, a pattern that was not consistently found in those with mTBI only. Among the several cortical regions with significant age-by-group interactions were bilateral posterior cingulate cortex (left:  = 0.03; right:  = 0.02), isthmus of the cingulate (left:  = 0.016; right:  = 0.001), and lateral orbitofrontal cortex (left:  = 0.038; right:  = 0.02). It is possible that these findings are related to a larger pattern of premature neurodegeneration and age-acceleration noted in those with long-term PTSD.