Abstract
IntroductionRepetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE). Our objectives were to: 1) characterize the magnitude and persistence of RHI-induced white matter (WM) changes; 2) determine their relationship to kinematic measures of RHI; and 3) explore their clinical relevance.MethodsProspective, observational study of 10 Division III college football players and 5 non-athlete controls during the 2011-12 season. All subjects underwent diffusion tensor imaging (DTI), physiologic, cognitive, and balance testing at pre-season (Time 1), post-season (Time 2), and after 6-months of no-contact rest (Time 3). Head impact measures were recorded using helmet-mounted accelerometers. The percentage of whole-brain WM voxels with significant changes in fractional anisotropy (FA) and mean diffusivity (MD) from Time 1 to 2, and Time 1 to 3 was determined for each subject and correlated to head impacts and clinical measures.ResultsTotal head impacts for the season ranged from 431–1,850. No athlete suffered a clinically evident concussion. Compared to controls, athletes experienced greater changes in FA and MD from Time 1 to 2 as well as Time 1 to 3; most differences at Time 2 persisted to Time 3. Among athletes, the percentage of voxels with decreased FA from Time 1 to 2 was positively correlated with several helmet impact measures. The persistence of WM changes from Time 1 to 3 was also associated with changes in serum ApoA1 and S100B autoantibodies. WM changes were not consistently associated with cognition or balance.ConclusionsA single football season of RHIs without clinically-evident concussion resulted in WM changes that correlated with multiple helmet impact measures and persisted following 6 months of no-contact rest. This lack of WM recovery could potentially contribute to cumulative WM changes with subsequent RHI exposures.
Highlights
Repetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE)
Concussions are a frequent occurrence among athletes involved in contact sports such as American football, ice hockey, soccer, and lacrosse (1.6–3.8 million/year [1]), repetitive head impacts (RHI) that do not result in concussion are even more common
Subjects Male athletes were recruited from the University of Rochester (UR) football team, which competes in National Collegiate Athletic Association Division III
Summary
Repetitive head impacts (RHI) sustained in contact sports are thought to be necessary for the long-term development of chronic traumatic encephalopathy (CTE). Using helmet-based accelerometers, estimates of the average number of RHIs in a single football season range from 244 to 1,444 per collegiate athlete [2,3], and from 175 to 1,410 per high school athlete [2,4]. Among high school athletes who did not experience concussion, RHIs during a single season of football were associated with abnormal regional cortical activation patterns on functional MRI [9,10]. The magnitude of this activation correlated with the number of RHIs sustained during the season, and resembled that previously reported in subjects with frank concussion [11]. Poorer post-season reaction time and scores on the Trail Making test of visual attention and task switching were found to be associated with greater head impact exposures [12]
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