The relationship between structural changes in mTBI and persistent PCS: DTI and cortical thickness analysis

Mild traumatic brain injury (mTBI) can induce persistent somatic, affective and cognitive symptoms, collectively known as post-concussion syndrome (PCS). It is debated whether this syndrome is due to biological or psychological factors. Standard structural imaging only detects lesions in a small proportion of those with mTBI, and these lesions are not associated with PCS in the acute ( 3 months) stage. However, microlesions and diffuse axonal injury (DAI) have been observed using novel imaging techniques such as diffusion tensor imaging (DTI). White matter damage examined in acute and post-acute/chronic mTBI has been correlated with cognitive and behavioural measures, as well as outcome from injury. Increased damage within the white matter tracts of the corpus callosum and thalamic radiations is observed in those with poorer outcome at 3 months, whereas grey matter damage is independent of outcome. This present study aims to investigate the relation of structural changes and long-term consequences in more detail by assessing the correlation between DTI-based indices and persistent PCS symptomatology. Structural changes were investigated in participants with chronic (>1 year) mTBI and persistent PCS (n¼10), participants with mTBI and no on-going PCS (n¼8) and non-head injured controls (n¼10). Fractional Anisotropy (FA) and cortical thickness were compared between groups to assess white matter integrity and focal damage respectively. In addition, the association between neural structure and level of PCS symptom report was evaluated. We hypothesised that long fibre white matter bundles, such as the corpus callosum, would be damaged in participants with chronic mTBI, with cortical thinning around these areas. Furthermore, we hypothesised that this damage would be related to the persistent PCS symptoms seen after mTBI. If PCS has a biological basis, then participants with mTBI and persistent PCS may have sustained greater damage to these areas at the time of injury than participants without ongoing symptoms. Preliminary analysis demonstrates a reduction in cortical thickness and white matter integrity in participants with chronic (>1 year) mTBI, independent of PCS, compared to controls. Diminished cortical thickness and white matter integrity were seen for cingulate cortex and corpus callosum. In addition, similar reductions were observed when comparing mTBI participants without PCS to those with PCS. This suggests that persistent PCS may have a biological element, with those reporting greater symptoms in the chronic state sustaining greater damage at the time of injury. Future research will investigate the correlation between the constituent symptoms of PCS (cognitive, affective, somatic) and structural damage in order to allow more definitive brain-behaviour associations