PTSD, but not history of mTBI, is associated with altered myelin in combat-exposed Iraq and Afghanistan Veterans

Objective: To investigate the biological, cognitive, and psychological presentations of combat-exposed Veterans with a history of mild traumatic brain injury (mTBI) and/or posttraumatic stress disorder (PTSD) using a novel white matter imaging technique and comprehensive neuropsychological assessment. Method: 74 Iraq and Afghanistan Veterans (mean age 33.89, 90.5% male) with history of mTBI (average 7.25 years since injury), PTSD, both, or neither underwent magnetic resonance imaging (MRI) exams including acquisition of a novel imaging technique, multicomponent-driven equilibrium single-pulse observation of T1/T2 (mcDESPOT) to quantify myelin water fraction (MWF), a surrogate measure of myelin content. Participants also underwent comprehensive neuropsychological assessment and three cognitive composite scores (memory, working memory/processing speed, and executive functioning) were created. Results: There were no significant group differences on the neuropsychological composite scores. ANCOVAs revealed a main effect of PTSD across all a priori regions of interest (ROI) in which PTSD was associated with higher MWF. There was no main effect of mTBI history or TBI by PTSD interaction on any ROI. Significant positive associations were observed between myelin and PTSD symptoms, but no significant associations were found between myelin and neurobehavioral symptoms. No significant associations were found between myelin in the a priori ROIs and the cognitive composite scores. Conclusion: This study did not find neuropsychological or MWF differences in combat Veterans with a remote history of mTBI but did find myelin alterations related to PTSD. Psychological trauma should be a primary target for intervention in Veterans with comorbid PTSD and mTBI reporting subjective complaints, given its salience.