Longitudinal change in regional brain volumes with exposure to repetitive head impacts

OBJECTIVE: This study tests the hypothesis that certain MRI-based regional brain volumes will show reductions over time in a cohort exposed to repetitive head impacts (RHI). METHODS: Participants were drawn from the Professional Fighters Brain Health Study, a longitudinal observational study of professional fighters and controls. Participants underwent annual 3T brain MRI, computerized cognitive testing, and blood sampling for determination of neurofilament light (NfL) and tau levels. Yearly change in regional brain volume was calculated for several predetermined cortical and subcortical brain volumes and the relationship with NfL and tau levels determined. RESULTS: A total of 204 participants who had at least 2 assessments were included in the analyses. Compared to controls, the active boxers had an average yearly rate of decline in volumes of the left thalamus (102.3 mm(3)/y [p = 0.0004], mid anterior corpus callosum (10.2 mm(3)/y [p = 0.018]), and central corpus callosum (16.5 mm(3)/y [p = <0.0001]). Retired boxers showed the most significant volumetric declines compared to controls in left (32.1 mm(3)/y [p = 0.002]) and right (30.6 mm(3)/y [p = 0.008]) amygdala and right hippocampus (33.5 mm(3)/y [p = 0.01]). Higher baseline NfL levels were associated with greater volumetric decline in left hippocampus and mid anterior corpus callosum. CONCLUSION: Volumetric loss in different brain regions may reflect different pathologic processes at different times among individuals exposed to RHI.