For those who study safety issues in combative and contact sports a useful article was published in the latest edition of Neurotrauma and Critical Care News discussing the state of science connecting CTE and other brain injury to contact sports.
The article, titled “Head Impacts in Contact Sports and Long-Term Brain Degeneration” offers an easy to read, plain English summary of what’s known and what still needs to be explored in the world of repetitive head trauma from sports and CTE.
In addressing CTE specifically the authors note as follows:
A 2016 National Institutes of Health (NIH) expert neuropathological panel established that the pattern of CTE is unlike any other form of brain degenerative disease with the collections of NFT or NT occurring in a unique and distinguishing pattern (3). It is believed that the more superficial and frontal areas of the brain are involved due to the direct contact with sports-related head impacts.
These pathophysiological features are associated with a characteristic behavioral syndrome for CTE, with symptoms in four categories: cognition, behavior, mood and occasionally motor. Behavioral changes include amplified aggression, increased impulsiveness, impaired judgment, and risk taking acts. Most often, a 6- to 12-year latency period following retirement from contact sports is then associated with failure in business, financial and marital relationships, homelessness, drug and/or alcohol abuse, depression, mild cognitive impairment and dementia, and many CTE sufferers commit suicide. Researchers have reported that CTE can be considered in two major clinical categories, with one group whose initial features develop at a younger age involving behavioral and/or mood disturbance and another group whose initial symptoms develop later in life and involve cognitive impairment. The language function is usually normal, but intelligence is often ultimately affected by the numerous effects described above (4).
While the risk of developing CTE has historically been discussed in the context of concussive injury and extensive neurotrauma exposure, emerging evidence indicates that a history of diagnosed or major concussions is not a requirement, but instead, repetitive subconcussive injury may play a prominent role in CTE development (5). This finding is based upon lack of documented concussive injury in numerous individuals diagnosed with CTE, although lack of self-reporting by athletes was common, and concussion without loss of consciousness was not recognized and treated as seriously as it is today. Evidence related to subconcussive injury and possible predilection to neurodegenerative disease includes the documented rates and severity of impacts in football linemen, a position in which retired athletes have been diagnosed with CTE (5). Additional evidence is the demonstration of neuroimaging and cognitive changes in those without a history of documented concussions as well as laboratory evidence indicating cellular and ultrastructural alterations without changes in levels of alertness or behavior. Despite the large number of people exposed to concussive and subconcussive injury through various sports and military service, CTE appears problematic for only a small subset of the population exposed to neurotrauma. Nonetheless, we currently do not know the incidence and prevalence of CTE since there has been no longitudinal study conducted to substantiate estimates of several prominent CTE research groups. The largest review to date, Maroon et. al., surveyed the clinical findings in all 153 CTE cases reported in the literature and found that 63 had a history of participation in football with majority of these having played at the professional level (6). The most common age at death of individuals with CTE was the range of 60 to 69, with 72.7 percent dying before the age of 70 (6).
Identification of other variables involved as risk factors for CTE remains in its early stage with speculation that genetics and lifestyle may be implicated. Just as in other forms of neurodegeneration such as Alzheimer’s disease, it has been postulated that the role of the ApoE ε4 (ApoE4) allele may be a susceptibility factor for the development of CTE; however, this has yet to be borne out.
Research continues to try to identify who is at greatest risk for getting concussions and ultimately, CTE. More studies are needed to follow former athletes over many years in order to know the true prevalence of CTE. A major focus of CTE research is investigating confirmation of the diagnosis of CTE in living individuals with several promising imaging technologies being evaluated, with F18DDNP PET imaging for tau and amyloid protein labeling being the most advanced (7).
Currently, there are no established treatments for CTE; therefore, reducing the risk for CTE development becomes the primary goal by limiting the exposure to concussive and subconcussive head impacts. There have been numerous positive changes in recent years involving contact sports, particularly football, resulting in greater safety for all participants. These include limiting contact in practice, eliminating head-to-head hits in practice drills, rule changes to penalize and prohibit egregious cranial hits, improvements in helmet design, new technology, such as helmet sensors and efforts to mitigate brain slosh, among others. It is hoped that in the near future CTE will be eliminated in contact sport athletes, but in the meantime, the possibility and implications of repetitive head trauma causing long-term effects, including brain degeneration, should be understood.