Diffusion Measures Indicate Fight Exposure-Related Damage to Cerebral White Matter in Boxers and Mixed Martial Arts Fighters

Abstract

BACKGROUND AND PURPOSE: Traumatic brain injury is common in fighting athletes such as boxers, given the frequency of blows to the head. Because DTI is sensitive to microstructural changes in white matter, this technique is often used to investigate white matter integrity in patients with traumatic brain injury. We hypothesized that previous fight exposure would predict DTI abnormalities in fighting athletes after controlling for individual variation.

A Longitudinal Diffusion Tensor Imaging Study Assessing White Matter Fiber Tracts after Sports-Related Concussion

“…Although these data do not inform us about the absolute maxima and minima of the diffusion metric trajectories because of the absence of measurements between 2 weeks and 2 months postinjury, the statistical trend detected by the between-group analyses at 2 months suggests a minor relapse in the recovery of the structural measures of WM integrity. This finding, taken together with the observed variability in the trajectories of RD and FA between 2 weeks and 2 months, might be reflective of the athletes' exposure to subconcussive hits following return to play (see earlier discussion 11,33,68 ). A more recent study, 87 and the first to relate diffusion measures to biomarkers in athletes with subconcussive hits, reported a positive correlation between the percentage change in football post-minus preseason levels of serum autoantibodies of the astrocytic protein, S100B (considered a peripheral marker of blood-brain barrier dysfunction), and the percentage of voxels with changes in MD during the corresponding time period.…”

“…These studies 11,33 suggest that RD might be a potentially sensitive measure to subconcussive hits. A recent DTI study 68 on cerebral WM in 74 boxers and 81 mixed martial arts fighters found that a history of previous knockouts (the ''knockout'' measure includes ''technical knockouts'' with no subsequent LOC) could predict increased RD in the CC, isthmus of the cingulate gyrus, pericalcarine sulcus, the precuneus, and the amygdala in the group of boxers. The same regions had increased MD and decreased FA values.…”

“…The investigators note that the continued expression of the positive clusters is inconsistent with cytotoxic edema, which drives ionic edema and signals a premorbid cellular process leading to necrotic cell death. 78 In discussing these findings, other researchers 68 suggest the possibility that contact sport athletes represent a distinct population because of their continued exposure to subconcussive hits leading to constant WM injury and recovery cycles and therefore might present a different recovery profile from the civilian, non-contact-sport population suffering a single mTBI episode. It must be noted that at least one study on SRC 79 showed significantly higher FA, AD, and lower MD (as compared to noncontact controls) values at two time points: *81 hours (on average) and 6 months postinjury, suggesting no significant recovery in diffusion measures during that time interval.…”

“…These findings suggest that subject specific exposure to subconcussive hits after return to play may be a potential factor affecting recovery of diffusion measures. 32,87 Further, variability in the trajectories of the diffusion measures might be affected by differences in number of previous concussions, 68 timing of each athlete's return to play (see Table 1), and individual genetic predisposition. 88,89 Experimental designs of future studies should include the assessment of subconcussive hits, extending at least to the end of season.…”

Advanced magnetic resonance imaging and neuropsychological assessment for detecting brain injury in a prospective cohort of university amateur boxers

“…Increasingly sophisticated analysis methods of structural imaging data have been developed enabling measurement of grey matter thickness and density, subcortical volume changes, and white matter microstructure at the voxel level for the whole brain. Recent studies that have applied these methods to participants with concussion from a variety of different sports (predominantly American Football, Football, Ice Hockey, and Mixed Martial Arts) have revealed convergent trends for concussion exposure to be related to reduced cortical thickness (Koerte et al, 2015, Albaugh et al, 2015, Tremblay et al, 2013), smaller subcortical structure volumes (Bernick et al, 2015a, Singh et al, 2014), and altered white matter diffusion metrics (Lancaster et al, 2016, Meier et al, 2015, Stamm et al, 2015, Wilde et al, 2015, Tremblay et al, 2014, Shin et al, 2014, Bazarian et al, 2014, Hart et al, 2013, Virji-Babul et al, 2013). Additionally, these findings have often corresponded to impaired neuropsychological function but appear to be more persistent, suggesting a biomarker of longer-term structural alteration.…”