Fight Exposure Linked to Reduced Brain Volume

Pauline Anderson

February 02, 2015

The more boxers and martial arts practitioners experience head trauma, the more likely they are to have lower brain volume, particularly caudate and thalamus volume, according to a new study.

Lower brain volume in these fighters correlated with reduced processing speed, the study also found.

These results "suggest that greater exposure to head trauma is related to detectable brain structural and performance deficits in active fighters," the authors, led by Charles Bernick, MD, Lou Ruvo Center for Brain Health, Cleveland Clinic, Las Vegas, Nevada, conclude.

The study was published online January 29 in the British Journal of Sports Medicine.

Fight Exposure

The analysis included 224 adults, aged 18 to 44 years, who were participants in the Professional Fighters Brain Health Study, a longitudinal cohort study of boxers and mixed martial arts (MMA) fighters. The participants included 93 boxers and 131 MMA fighters.

The length of professional fighting in this group ranged from 0 to 24 years, with a mean of 4 years. The number of professional fights ranged from 0 to 101, with a mean of 10 fights.

The study also included a control group of 22 age- and education-matched participants with no history of head trauma who did not play a sport associated with head injuries from high school onward.

Participants were assessed at baseline and then annually for 4 years. Researchers measured cognitive function with a computer-based battery consisting of tests of verbal memory, processing speed, and other functions. They used MRI to assess brain volumes.

Researchers also evaluated the Fight Exposure Score (FES), which considers duration and intensity of fights. FESs range from 0 to 4, with 4 representing the greatest exposure.

The study found that increasing exposure to head trauma, as measured by the number of professional fights or years of professional fighting, was generally associated with lower brain structural volumes, particularly subcortical structures. The most consistent relationship between exposure variables and brain volume was seen in the thalamus and caudate.

Cortex "Gateway"

The thalamus acts as a "gateway" to the cortex and when affected can influence many neurologic functions, said the authors. It and the caudate are vulnerable to volumetric loss through several mechanisms. Rotational movement of the head brought on by punches in boxing or MMA can result in diffuse axonal injury in white matter tracts, they note.

For the most part, brain structure volumes were lower for boxers than MMA fighters or controls. This could be due to several factors, the authors write.

"Perhaps the most obvious explanation is that boxers get hit in the head more. In addition to trying to concuss (ie, knock out) their opponent, MMA fighters can utilise other combat skills such as wrestling and jiu jitsu to win their match by submission without causing a concussion."

The study also found that processing speed was correlated with reduced volume in several cortical and subcortical structures. Reduction in processing speed, said the authors, is consistent with repeated concussions and is considered a clinical component of chronic traumatic encephalopathy.

The FES turned out to be a useful tool to identify affected fighters. Each exposure in FES was associated with reductions of 0.8%, 0.9%, and 0.8% in volumes of the caudate, amygdala, and thalamus, respectively. About 1 in 4 fighters with an FES of 3 or 4 scored in an impaired range on tests of verbal memory compared with only about 1 in 10 of those who had an FES of 0.

"Pending review of its performance longitudinally and replication of our findings in a larger cohort of fighters, the FES (or some modification of it) may be an easy to use, practical tool that can select out fighters that may be more likely to have cognitive impairment or be going down that road," write the authors.

The study sample was not a random sample of fighters but was self-selected; as a result the participants may be less skilled or more susceptible to be knocked out. Another potential study limitation was that the measures of exposure to head trauma were indirect and may not truly reflect the actual degree of head trauma.

The authors also acknowledged that the computerized cognitive test battery was not comprehensive and that the relationship between exposure and brain volumes and cognition may have been due to other factors related to exposure and not the exposure itself.

The authors have disclosed no relevant financial relationships.

Br J Sports Med. Published online January 29, 2015. Abstract

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