Study – 41% of Retired Fighters Likely Have CTE – The More Bouts the Higher the Risk

New research was published this week in the British Journal of Sports Medicine shedding more light on the prevalence of the progressive brain disease CTE in the combat sports community.

In the study, titled Traumatic encephalopathy syndrome: application of new criteria to a cohort exposed to repetitive head impacts, the authors accessed data from the Professional Athletes Brain Health Study. 176 combat sports athletes participated (boxers and MMA fighters). The authors applied the Consensus Diagnostic Criteria for Traumatic Encephalopathy Syndrome (“TES” which are the criterial for when someone is suspected to have CTE while alive since a formal diagnosis cannot be made until death). They found that 41% of the participants had TES.

Of the TES positive group the authors then compared MRI brain volumes, cognitive testing results and certain biomarkers to see the difference in these objective findings compared to the group without TES. They found that the TES group had differences in brain volume and reduced cognitive testing results leading them to conclude that using the Consensus Diagnostic Criteria for Traumatic Encephalopathy Syndrome have value when studying harm from repetitive head impacts.

In discussing the prevalence of CTE among fighters in the study and the risk factors the authors noted as follows:

One of the outstanding questions regarding CTE is the incidence and prevalence in various groups exposed to RHI. The prevalence of TES in our entire cohort of retired professional fighters and those over the age of 35 was 41% and increases with age. More than 60% of retired fighters above the age of 50 met criteria for TES…

The heterogeneity of previous cohorts studied makes it difficult to compare our findings to prevalence rates reported in the literature. In the initial description of CTE, Martland claimed that 50% of boxers had symptoms of what was termed ‘punch drunk’.20 One of the most extensive epidemiological study of boxers performed over 50 years ago on 250 randomly selected retired fighters in Great Britain found that 17% had what would be considered CTE and 40% with some neurological findings or alcoholism.21 Using the NINDS Consensus pathological criteria, postmortem studies have indicated rates of CTE ranging from 32% of individuals who had a history of playing contact sports in the Mayo Clinic Brain Bank, to 99% of former National Football League players in the Boston University Brain Bank.

Aside from age, we found the major factor associated with TES+ in our group was amount of exposure to RHI.. Looking at boxers in our cohort, we found that a threshold of 25 or more fights predicted whether a patient was categorised as TES+, though the sensitivity and specificity of this was relatively low (72 and 64, respectively). This finding may help guide required exposure levels for combat sports in future iterations of the TES criteria, but further data modelling may be improved by incorporating other factors that can be easily assessed such as frequency of competitions, age of starting fighting or number of knock outs.

While it may be that anyone given enough exposure to RHI will develop TES, other factors have been reported to interact with exposure to determine an individual’s long-term neurological outcome from RHI.23 Of note, and similar to previous findings in our cohort and others, age at which one starts exposure to RHI may be a risk factor for worse performance and TES

The full abstract reads as follows:


Objective To examine the characteristics of those who fulfil the recent National Institute of Neurological Disease and Stroke (NINDS) Consensus Diagnostic Criteria for Traumatic Encephalopathy Syndrome (TES) and test whether they show differences in MRI-based regional brain volumes, cognitive domains, and certain plasma biomarkers.

Methods Professional fighters 35 years of age or older and/or retired were included. Participants were categorised as either having TES (TES+) or not (non-TES). TES+ participants were further subtyped by their cognitive profile. Multiple linear regression models were used to compare MRI-based regional brain volumes, cognitive performance, plasma tau and neurofilament light levels between TES– and TES+ groups.

Results 176 participants (110 boxers and 66 MMA) were included in the analysis. 72 (41%)/176 were categorised as having TES, the likelihood of TES increasing with age. TES+ participants tended to be boxers, started fighting at a younger age, had more professional fights and knocked out more frequently. The TES+ group had lower regional brain volumes including both grey and white matter structures. TES+ also had lower scores on simple and choice reaction time, psychomotor speed and Trails A .

Conclusion The new TES criteria does distinguish a group of fighters with differences in regional brain volumes and reduced cognitive function. Our findings support the use of the NINDS criteria for TES in further research of the long-term effects of repetitive head impacts.


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