Persistent, Long-term Cerebral White Matter Changes after Sports-Related Repetitive Head Impacts

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.

The Influence of Head Impact Threshold for Reporting Data in Contact and Collision Sports: Systematic Review and Original Data Analysis

“…These did however vary for studies reporting impacts that occurred during matches only, those that were recorded for both match and training activities and those that combined both match and training activity impacts. More than half (52%) of the studies 6 6 These changes post season imply a relationship between the number of RHI's that occur over a season of American football and white matter injury, despite no clinically evident concussion being recorded. 6 The inclusion of impact tolerances and impact severity levels may also assist with the identification of players at risk of possible long term injuries.…”

“…More than half (52%) of the studies 6 6 These changes post season imply a relationship between the number of RHI's that occur over a season of American football and white matter injury, despite no clinically evident concussion being recorded. 6 The inclusion of impact tolerances and impact severity levels may also assist with the identification of players at risk of possible long term injuries. This may also act as an indicator of when to rest players if they are exposed to RHI's above these impact tolerances (>4,500 rad/s 2 and >6,000 rad/s 2 ).…”

Age at First Exposure to Football Is Associated with Altered Corpus Callosum White Matter Microstructure in Former Professional Football Players

“…56,57 The greatest shear strain occurs in the genu (anterior CC) and splenium (posterior CC), 57 and these regions are frequently damaged in TBI. 26,[56][57][58][59][60] Studies also report CC microstructural damage following prolonged exposure to RHI in football, 49 hockey, 50 and soccer players. 5 Further, several neuroimaging studies in children demonstrate disrupted CC development following TBI of varying severity.…”

“…Recent research using DTI, 5,[48][49][50][51] as well as other imaging modalities, 52-55 also revealed altered brain structure and connectivity following prolonged exposure to RHI. Further, several studies report altered diffusivity following just one season of football 48,49,51 and ice hockey 50 play, when comparing preseason and post-season DTI measures. Bazarian and colleagues 49 identified decreased FA and increased mean diffusivity values that persisted for at least 6 months post-season.…”

“…Further, several studies report altered diffusivity following just one season of football 48,49,51 and ice hockey 50 play, when comparing preseason and post-season DTI measures. Bazarian and colleagues 49 identified decreased FA and increased mean diffusivity values that persisted for at least 6 months post-season. Moreover, Koerte and colleagues 5 compared elite adult soccer players with no history of concussion (i.e., only subconcussive blows to the head) to competitive swimmers and observed higher RD and AD in several brain regions.…”