Reader Response: Longitudinal Changes of Brain Microstructure and Function in Nonconcussed Female Rugby Players

We read the article by Manning et al.1 with interest. Studies of professional contact-sports athletes have made clear that exposures to repetitive head impacts over decades are associated with late-life neurodegenerative dementia.2,3 It is less clear whether participation in contact sports at the amateur level results in comparable risks. The study by Manning et al. found white matter (WM) microstructural disruption—especially in the corpus callosum and impaired functional connectivity in the default mode network over time in concussion-free and asymptomatic female rugby players—using diffusion tensor (DTI) and resting-state connectivity MRI (rsMRI), respectively.1 These WM tracts are known to be disrupted as a consequence of more severe traumatic brain injuries.4 In contrast to the existing studies,5 Manning et al. assessed WM and functional changes in female athletes and noncontact sport athletes longitudinally, which is a novel and strong study design. Although the results of the Manning et al. study are compelling, they should be interpreted with caution. Although DTI and rsMRI are sensitive for identifying WM disruption, it is likely that there is substantial cognitive reserve built into brain and that these elegant imaging techniques may detect small degrees of disruption that are unlikely to result in functional limitations. Future studies with larger sample sizes and longer follow-up will be required to answer this important question. Finally, the DTI and rsMRI methods have several limitations, including limited availability and cumbersome image processing, which limits their usefulness for routine assessment of athletes. Future studies should include blood-based biomarkers, such as neurofilament light and glial fibrillary acidic protein, which are inexpensive and straightforward to interpret, as markers of axonal disruption. How well blood biomarkers correlate with the imaging biomarkers of axonal injury after concussive and subconcussive head impacts is a critical issue which remains to be resolved.

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