Increased diffusion in the brain of professional boxers: a preclinical sign of traumatic brain injury?

Abstract

Background and purpose: Professional boxing is associated with chronic, repetitive head blows that may cause brain injuries. Diffusion-weighted imaging is sensitive to microscopic changes and may be a useful tool to quantify the microstructural integrity of the brain. In this study, we sought to quantify microscopic alterations associated with chronic traumatic brain injury in professional boxers.

Methods: MR and diffusion-weighted imaging were performed in 24 boxers and in 14 age- and sex-matched control subjects with no history of head trauma. Using distribution analysis, the average diffusion constant of the entire brain (BD(av)) and diffusion distribution width (sigma) were calculated for each subject; findings in professional boxers were compared with those of control subjects. In the boxer group, correlations between diffusion changes and boxing history and diffusion changes and MR imaging findings were assessed.

Results: The measured diffusion values in the boxer group were significantly higher than those measured in the control group (BD(av), P <.0001; sigma, P <.01). In the boxer group, a robust correlation was found between increased BD(av) and frequency of hospitalization for boxing injuries (r = 0.654, P <.05). The most common MR finding in the boxer group was volume loss inappropriate to age followed by cavum septum pellucidum, subcortical white matter disease, and periventricular white matter disease.

Conclusion: Boxers had higher diffusion constants than those in control subjects. Our data suggest that microstructural damage of the brain associated with chronic traumatic brain injury may elevate whole-brain diffusion. This global elevation can exist even when routine MR findings are normal.

Fig 1.

Normalized brain diffusion distribution histograms in a control subject and a boxer (case 15). The areas under the two curves are the same. The D_av data (dots and circles) are fitted with a triple Gaussian function to represent the two-compartment nature and the mixing between the two compartments (lines). The narrow peak represents the distribution of the brain tissue about its mean. The second and the third compartments have a broader distribution. The mean of the brain tissue pixel distribution is recognized as a mean diffusion constant for the entire brain (BD_av). The distribution width (σ) of the brain tissue compartment is also recorded. The fitted curve of the boxer (circles) shifts to the right as compared with the curve of the control subject (dots). The second compartment level of the boxer’s curve is higher than that of the control subject.

Fig 2.

BD_av versus σ for boxers and control subjects: Overall, the boxer group shows elevated BD_av and σ.

Fig 3.

Representative images of MR findings in boxers: A, Cavum septum pellucidum (case 14); B, nonspecific periventricular white matter disease (case 22); and C, mild subcortical white matter demyelination (case 21).