Postconcussional disorder and PTSD symptoms of military‐related traumatic brain injury associated with compromised neurocircuitry

Abstract

Traumatic brain injury (TBI) is a common combat injury, often through explosive blast, and produces heterogeneous brain changes due to various mechanisms of injury. It is unclear whether the vulnerability of white matter differs between blast and impact injury, and the consequences of microstructural changes on neuropsychological function are poorly understood in military TBI patients. Diffusion tensor imaging (DTI) techniques were used to assess the neurocircuitry in 37 U.S. service members (29 mild, 7 moderate, 1 severe; 17 blast and 20 nonblast), who sustained a TBI while deployed, compared to 14 nondeployed, military controls. High-dimensional deformable registration of MRI diffusion tensor data was followed by fiber tracking and tract-specific analysis along with region-of-interest analysis. DTI results were examined in relation to post-concussion and post-traumatic stress disorder (PTSD) symptoms. The most prominent white matter microstructural injury for both blast and nonblast patients was in the frontal fibers within the fronto-striatal (corona radiata, internal capsule) and fronto-limbic circuits (fornix, cingulum), the fronto-parieto-occipital association fibers, in brainstem fibers, and in callosal fibers. Subcortical superior-inferiorly oriented tracts were more vulnerable to blast injury than nonblast injury, while direct impact force had more detrimental effects on anterior-posteriorly oriented tracts, which tended to cause heterogeneous left and right hemispheric asymmetries of white matter connectivity. The tractography using diffusion anisotropy deficits revealed the cortico-striatal-thalamic-cerebellar-cortical (CSTCC) networks, where increased post-concussion and PTSD symptoms were associated with low fractional anisotropy in the major nodes of compromised CSTCC neurocircuitry, and the consequences on cognitive function were explored as well.

Compromised Neurocircuitry in Chronic Blast‐Related Mild Traumatic Brain Injury

“…These results are similar to our previous report [Yeh et al, 2014] and other reports of chronic changes in military-related blast mTBI [Mac Donald et al, 2011] using voxel-wise analysis for group comparison. In addition, newer approaches using tract profile analyses were useful in group comparison and single subject analysis, which pinpoint specific damaged fiber tracts and affected neurocircuitry.…”

“…3 and 4) are vulnerable to blast injury. These results were consistent with our previous DTI and tractography report in subacute TBI patients [Yeh et al, 2014] that revealed subcortical superior-inferiorly oriented tracts were particularly vulnerable to blast injury, as well as other reports of chronic changes in mTBI, either military personnel [Mac Donald et al, 2011] or civilian populations [Inglese et al, 2005;Kraus et al, 2007;Lipton et al, 2009]. The anatomical locations of low FA using tract specific analysis and tract profile analysis in this study are also consistent with the results from using mechanical simulation and finite element analysis of brain exposure to blasts, showing that the highest level of axonal shear/ strain effects developed in the regions of corpus callosum and corona radiata [Chatelin et al, 2011] in mTBI model.…”

The effect of preprocessing in dynamic functional network connectivity used to classify mild traumatic brain injury

“…This correlation enhancement can be explained by a compensatory mechanism for detrimental sensorial symptoms in mTBI patients (Sours et al., 2015). Structural corticothalamic abnormalities of white matter in TBI patients are linked to more serious symptoms including posttraumatic stress disorder (Yeh et al., 2014). Obtained results cannot directly explain decreased connectivity linked to the DMN reported by previous studies (Bonnelle et al., 2011; Sharp, Scott, & Leech, 2014; Sharp et al., 2011).…”

Explosive Blast Mild Traumatic Brain Injury

“…On the contrary, disruption in WM-integrity allows diffusion of water away from the WM, indicated by a decrease in FA and increases MD. There are several DTI studies of veterans where loss of WM-integrity predicts mTBI [28][29][30]. A study of 125 veterans, 2-5 years post-deployment, indicated that mild TBI was correlated with number of deployments and increased PCS, however, indicated normal WM-integrity on DTI [23].…”