Diffusion anisotropy changes in the brains of professional boxers

Abstract

Background and purpose: Professional boxing may result in brain injury. We hypothesize that quantitative MR diffusion imaging may be useful in determining early white matter changes.

Methods: Forty-nine professional boxers (age 30 +/- 4.5 years) and 19 healthy control subjects (age 32 +/- 9.5 years) were imaged on a clinical 1.5T scanner. None of the subjects had neurologic disorder or deficit. The average diffusion constant (D(av)) and diffusion anisotropy (FA) were determined pixel by pixel. Regional diffusion measurements were done in the corpus callosum (CC) and internal capsule (IC). The whole brain diffusion constant (BD(av)) was also determined. Student t test was used to analyze the diffusion difference between boxers and the healthy control subjects. P < .05 was considered statistically significant.

Results: Of the 49 professional boxers, 42 had normal conventional MRIs. The remaining 7 boxers had abnormal MR imaging findings dominated by nonspecific white matter disease. There was a significant difference in diffusion and anisotropy measurements in all the boxers compared with the healthy control subjects. In the boxer group, BD(av) increased and FA decreased significantly in the CC and posterior limb of IC. The measured FA and D(av) inversely correlated in regions of CC and IC in boxers but not in healthy control subjects. BD(av) also robustly correlated with both FA and D(av) in the splenium of CC in boxers.

Conclusion: Increased BD(av) and the decreased FA in the CC and IC may represent preclinical signs of subtle brain injury in professional boxers.

Fig 1.

Illustration of regional diffusion and anisotropy measurements with ROIs in the genu CC, splenium CC, anterior IC, and posterior IC.

Fig 2.

Representative axial FLAIR images of subcortical white matter disease (A), periventricular white matter disease (B), and cavum septum pellucidum (C)

Fig 3.

Comparison of FA (A) and D_av (B) measurements between boxers and healthy control subjects. Compared with healthy control subjects, boxers overall and boxers with normal MR imaging have decreased FA in splenium CC (P < .05), genu CC (P < .005), and posterior IC (P < .05) and increased BD_av (P < .05) and D_av in both the anterior and posterior limbs of IC (P < .05).

Fig 4.

Robust correlations of D_av and FA in CC of all boxers (A) and boxers with normal MR imaging (B). For the genu CC, D_av = 1.23 − 0.66 × FA, r = 0.59, P < .001; for the splenium CC, D_av = 0.95 − 0.35 × FA, r = 0.37, P < .01. B, The group of boxers with normal MR imaging. For the genu CC (dots), D_av = 1.19 − 0.61 × FA, r = 0.55, P < .001; for the splenium CC (circles): D_av = 0.94 − 0.34 × FA, r = 0.34, P < .05.

Fig 5.

Diffusion anisotropy maps and diffusion tensor imaging-based white matter tractography of a representative boxer (A and B; 27 years old) and a control (C and D; 29 years old). Intensity is proportional to anisotropy and color shows the direction. The boxer has decreased anisotropy in CC and anterior and posterior limb of IC compared with the healthy control subjects. Fiber tracking showed overall fewer trackable white matter fibers in this boxer’s brain (B) compared with that of a control subject (D). The difference in fibers through the corpus callosum is particularly striking.

Fig 6.

Two boxers with a follow-up study with in 464 days (A) and 658 days (B) apart, respectively. Both boxers showed decreased trackable fibers within the whole brain as well as the corpus callosum compared with the initial study.