Associate Professor Mathew Summers
The relationship between a head injury and dementia is that people who sustain significant brain injuries in early adulthood, do show a slight increase in the risk for dementia in late adulthood. That link is because head injury results in pathological changes in the brain, both at the microscopic level in terms of changes to your neural connections throughout different parts of the brain, but also at the macroscopic level where we see large infarcts and areas of dead tissue.
The evidence again for the relationship between head injury and dementia is retrospective, not prospective, and there are ethical reasons why we can’t do a prospective randomised control trial and deliberately give a group of people a head injury and then see what happens to them. The only studies we can really do in humans, are looking at people who have sustained a head injury, and see whether or not they develop dementia. The difficulty we have is that if we look at the epidemiological evidence for head injuries, people at highest risks for a head injury are male, educated less than year 12, under the age of 25 at the time of injury, have low socioeconomic status to start with, and then subsequent to the head injury, will have educational and socioeconomic disadvantage. Those factors alone may account for why there is an increased risk of dementia in that cohort, because it’s difficult to compare that group of people then with a wider population, where we have 50% female and the education standards are different.
There is a new group of traumatic brain injuries that we are exploring in our research, that’s starting to appear in the research literature, and that’s related to sports related concussions, and particularly the risk of repetitive concussive injuries in contact sports. For instance, the sort of things we’re seeing out of the US relate to the NFL, the American Football League, where there are lots of concussive head injuries, which do not involve loss of consciousness. We’re seeing similar sorts of studies of AFL football players, rugby league players and rugby union players, as well as soccer players, in Australia. We were looking at the impact of those repetitive concussions. We have established evidence between boxing and dementia pugilistica, which is a form of dementia that arises from repetitive high impact concussive head injuries, but that’s specific to boxing. So the interest amongst competitive contact sports is, do we have an increased risk for seeing those sorts of outcomes in professional sports people who have repetitive injuries? There is some indication that there’s a risk. There are descriptions of a condition called CTE which involves pathological changes which have been detected in retired professional NFL players from the US. There are issues between sports, in terms of level and force of contact, that have to be worked out in terms of how they contribute. There are issues in terms of magnitude of concussion. There are issues, particularly in relation to sport, in terms of the age at which these concussions start. Most professional sports players commence their sport as children, and continue to play all the way through amateur and junior leagues. Do the concussions that happen that early on, carry more impact than the concussions that happen later on? So we don’t have the evidence yet, but there is sufficient concern at this stage that most sporting codes that involve contact sports have modified concussion rules, and we have very clear information and concussion rules particularly for junior sports. Rugby union was probably the first sport worldwide that brought in mandatory concussion reporting rules and taking players out of sport, particularly at junior levels, worldwide, and that is starting to influence every other professional code. Whether someone should be concerned about increased dementia risk from concussion, is difficult to be definitive about. There is possibly a link between the number of repeated concussions and the severity of those concussions, and dementia. That being said, the evidence isn’t firm yet, but it would most likely be dose dependent. That is, the sporting code rules would indicate that two concussions, of any form, within a season, should sideline a player for the rest of that season until medically cleared to resume playing, and that means cognitive testing to make sure that the brain functions are back to normal. So if we extend that risk, we need to monitor repeat concussions, and if a player starts to experience more than two concussions in a season, every season, they should probably reconsider their choice of sport and the potential for risks to future brain functions.