Towards Understanding Comprehensive Morphometric Changes and Its Correlation with Cognition and Exposure to Fighting in Active Professional Boxers

Abstract

Professional athletes exposed to repetitive head impacts are at increased risk for developing a progressive neurological syndrome known as traumatic encephalopathy syndrome and neuropathology seen on autopsy called chronic traumatic encephalopathy (CTE). The early identification of individuals at increased risk for CTE is important and the search for biomarkers is underway. In this study, we utilized data from a large cohort study to compare differences in regional brain volumes, cortical thickness, voxel-based morphometric (VBM)-derived measures, and graph-theoretical measures derived from large-scale topographical maps in active professional boxers. We compared the above morphometric measures between active professional boxers with low cognitive scores (impaired boxers) and active professional boxers with intact cognitive scores (nonimpaired boxers). The cognitive scores were evaluated through neuropsychological evaluation. As an exploratory analysis, we also examined the power of various machine-learning algorithms to identify impaired and nonimpaired boxers using both group-level regression-driven analysis and previously identified hypothesis-driven cortical thickness and volumetric measures. We found significant group-level differences between impaired and nonimpaired boxers in cortical thickness in a single brain region (right precuneus), differences in VBM-derived gray matter density encompassing the caudate, putamen, and thalamus; and white matter density encompassing the right paracentral lobule, but no differences in any graph-theoretical network properties. Additionally, we found that a priori hypothesis-driven T1-derived cortical thickness and volumetric analysis performed better than traditional regression-based analysis. Overall, this study suggests that neuroanatomical differences exist between impaired and nonimpaired active professional boxers, and that hypothesis-driven techniques are likely necessary to become reliable biomarkers.

Longitudinal Changes in Cognitive Functioning and Brain Structure in Professional Boxers and Mixed Martial Artists After They Stop Fighting

“…Previous studies, including our own studies, have reported cognitive impairments in active professional fighters that further correlate with fighters' RHI exposures 7,8,14 . In our current study, fighters who stopped fighting in their early 30s demonstrated improvements across measures of VM, PSS and PSY.…”

“…bilateral thalamus, since both cross-sectional and longitudinal volume loss of bilateral thalamus have been previously reported in this fighter's cohort 12,14,15 .…”

“…We primarily focused our analyses on cortical thickness measures, and additional analyses for volume measures were specifically performed at (1) regions demonstrating significant effects in cortical thickness analysis and (2) bilateral thalamus because both cross-sectional and longitudinal volume loss of bilateral thalamus have been previously reported in this fighter's cohort. 12,14,15 Details of MRI data analyses are included in eMethods (links. lww.com/WNL/C312).…”

“…Previous neuroimaging studies have identified various structural abnormalities in fighters' brains that have been associated with both exposure to RHI and subsequent declines in neuropsychological performance [9][10][11][12][13][14] . Changes in fighters' regional thalamic volumes have been reported both cross-sectionally and longitudinally in structural magnetic resonance imaging (MRI) data 11,12 , with greater regional volume loss associated with declines in cognitive functioning 11,14 . Grey matter morphometry changes encompassing the caudate, putamen, and thalamus have also been identified in fighters with declines in cognitive performance 15 .…”

“…11,14 Gray matter morphometry changes encompassing the caudate, putamen, and thalamus have also been identified in fighters with declines in cognitive performance. 15 Building from these works, we hypothesize that, after active fighters' transitions to inactive status, their brain regional measures derived from structural MRI data will stabilize or change differently from fighters who remain active, and these changes will correspond with the stabilization of their cognitive functions.…”