Abstract
To the Editor:
In his recent letter, 1 Dr. Hutchinson raises some important points regarding the imaging evaluation of acute mild traumatic brain injury (mTBI). We agree that attrition is an important consideration in longitudinal studies and the effects of attrition can be assessed by the Consolidated Standards of Reporting Trials (CONSORT) diagram we provided in our study. 2 We also agree that most acute mTBI patients experience substantial recovery during the weeks to months following their injury. Indeed, this may help explain another point Dr. Hutchinson made about the relative lack of involvement of the corpus callosum in our diffusion tensor imaging (DTI) study. White matter microstructural disruption of the corpus callosum was originally demonstrated in the clinical literature with DTI of chronic symptomatic mTBI patients 3,4 and may thus be linked to persistent injury. Our study suggests that callosal injury on DTI might not be as prominent a feature in an mTBI cohort with substantial recovery, rather than one with only long-term symptomatic individuals. More advanced diffusion magnetic resonance imaging technology such as neurite orientation dispersion and density imaging (NODDI) could provide more sensitive and specific biomarkers of the progression from acute mTBI to chronic cognitive and behavioral impairment than is possible with DTI. 5
Dr. Hutchinson also suggests that the regional distribution of white matter microstructural alterations found using DTI in our study overlaps with watershed regions prone to ischemia. While possible, there are also other special characteristics of these deep white matter zones as well, such as a high degree of connectome network connectivity due to a large proportion of long crossing fiber tracts. 6,7 The length and configuration of these white matter fibers may render them uniquely susceptible to biomechanical trauma and their importance to the whole-brain structural connectome may result in diverse cognitive and behavioral sequelae when disrupted. 8
Finally, Dr. Hutchinson suggests that incomplete recovery in mTBI may sometimes be associated with pre-existing psychological characteristics. We wholeheartedly agree, although an exclusive focus on secondary gain is much too narrow. We have recently shown a major effect of emotional resilience on the longitudinal DTI results that relate to the long-term disability and symptomatic outcomes in this mTBI cohort. 9 Hence, the effects of psychological factors such as resilience (“what the brain brings to the injury”) need to be considered in addition to the traditional biomechanical trauma paradigm (“what the injury brings to the brain”) for optimal TBI patient outcome prediction.