People need to stop confusing concussion with CTE. We have long known that multiple concussions can lead to some reduction in baseline cognitive skills and prolonged concussive symptoms (headache, dizziness, etc.). The symptoms are most severe immediately and get better over time. With only one mild uncomplicated mild TBI, the overwhelming majority of people are going to be just fine and fully recover. With multiple concussions, there is increased risk you may not make it back to full baseline. Still, most do.
CTE is supposedly a neurodegenerative disorder involving hyperphosphorylated tau aggregation. It is a degenerative disorder akin to Alzheimer's disease that results from repeated concussive or subconcussive blows. The evidence for CTE is not convincing at best, and is completely intellectually dishonest at worst. The narrative of the big bad NFL being like big tobacco is too sexy for media and lay people to let go, so you only hear statement like "what we know now" and "the evidence is so overwhelming." Seemingly very smart people believe there is an epidemic of contact sport athletes committing suicide, becoming violent and deranged, and dying earlier because they played a contact sport. In fact, the hard data show exactly the opposite.
Weir et al (2009) using a self-report survey of over 1000 retired NFL players showed NFL retirees aged 50+ reported having ‘Dementia (AD or other) more commonly than would be found in 6% vs. 2%. That is concerning, ignoring for the moment it is self report and not actual diagnosis (and that 94% of respondents didn't report dementia/memory problems). More interesting, depression rates were the same as general population (recent retirees slightly higher rates, but that is expected and otherwise all rates across ages were not statistically different). It also showed significantly lower rates (and I mean significantly) of anger-proneness/violence in retired NFL players.
Lehman et al., 2012 examined the causes of death in a cohort of 3439 NFL players with more than 5 playing seasons from 1959–1988 (using the pension fund database). Know what was found? Neurodegenerative mortality rate of NFL cohort was higher than the general population, but still the overall rate was lower than 5% of the cohort. So again, there may be increased risk of some form of dementia, but 95% have none. More interesting, overall rate of death due to any cause was much lower in retired NFL players than for U.S. men (age and race matched) in the general population. Only about 1/2 as many deaths in retired NFL sample as would be expected for similar aged men.
THIS IS THE BEST PART: the study also found retired NFL players much less likely to commit suicide. Rate of death due to suicide in retired NFL players is only 40% of general population. This finding has been replicated in at least two other subsequent meta-analyses, and is not a fluke. You are less likely to kill yourself if you are a retired NFL player.
So, what do we know for sure about CTE? We know that you have a slightly higher risk for developing dementia in late life, but even with that increased risk 95% will not. Depression is no more common than in the general public, and violent behavior and suicide are significantly less than in the general public. So, if CTE is an epidemic, then it is the weakest one ever.
So, you are probably asking how it is so many are getting diagnosed with CTE. The thing that is important to remember here is that all research in non-boxers since 2005 has essentially come from two camps (Bennett Omalu's camp in California, and Anne McKee's camp at BU). The hundreds of millions of dollars in research funding, the fame and notoriety, has all gone to these two. To say they are invested in this machine is an understatement. Both hold press conferences rather than subject themselves to peer review. Dr. McKee apparently won't take questions from other researchers, only the press. Omalu is in trouble for funneling money to his for-profit company from his non-profit research and is a fame seeker. He wouldn't allow McKee to be in the movie because he is such a narcissist. These two camps hate each other because they are in direct competition.
Here is what you need to know about the "overwhelming" research for CTE that they are producing. There is still only case studies. There are no control studies. There is no epidemiological studies. We literally have no idea how many concussions it would take to produce CTE, or how prevalent it is because those studies DO NOT EXIST. Omalu and McKee also have deviated from Corsellis et al's (1973) gold standard for diagnosing CTE to make it much easier to diagnose. The only element that is really necessary at this point is the tau protein aggregation in the brain. Tau is a microtubule associated protein thought to play a role in neuronal microtubule stability. When hyperphosphorylated, it leads to aggregation in the form of tangles.
Here is what you need to know about it. It is commonly found in people over 40 and it's accumulation correlates with age. While not common, even 10% of people under 20 years old who have no history of concussion are walking around just fine. I'd suggest looking at Braak et al. (2012) if you want to learn more about how common it is. They explored a series of 2332 random autopsies and it is just a fantastic study. We also know many things increase the likelihood of finding pathological tau in the brain, such as opiate use (which is very prevalent in the NFL and retirees due to their chronic pain). Some weaker studies even suggest bipolar disorder might be associated with greater tau accumulation, though I find those studies to be poorly done. Tau is associated with multiple forms of dementia, to include Alzheimer's disease and frontal-temporal dementia subtypes. Omalu and McKee suggest CTE is different because there is no beta amyloid, but almost 50% of their donated brains reportedly have evidence of amyloid and tau (the signature pathology of Alzheimer's). Some also have TDP-43 (ALS), and synuclien (Parkinsons/Lewy body dementia). FTD subtypes have all the same behavior described in CTE, starts in peoples 50s, and is a tau dementia. There is literally no way to differentiate it from CTE as defined by Omalu and McKee. The fact is that most of their donated brains are probably reflecting normal aging or another dementia.
You are probably asking now, what about those studies of boxers. You probably heard that we have known about CTE for 90 years. What you don't hear is that there has always been controversy about it because of poor research methodology. There was never a consensus about whether it was a progressive disease of something static. In fact, the term CTE stands for Chronic Traumatic Encephalopathy. The "chronic" literally meant it was supposed to be static and non-progressing, so it is funny that Omalu in 2005 decided to adopt this term from Miller (1966) rather than the competing terms such as dementia pugilistica or punch drunk. Controversy about CTE has always been present even before the NFL brought it to general awareness because there were only case studies (no controls), selection bias (only brains of boxers who were institutionalize were autopsied), and newer histological methods have shown that many of the brains studied originally and thought to lack amyloid are actually indistinguishable from Alzheimer's disease. In fact, it appears AD may have been the underlying issue in many of these older boxers.
I've spent way too much time writing something that nobody will read so I will stop now. But I hope this CTE craze ends soon. We are going to look back at this time period and be really embarrassed.
Braak H, Del Tredici K. Alzheimer’s disease: Pathogenesis and prevention. Alzheimer’s and Dementia 2012;8:227–233.
Cottler L, Abdallah B, Cummings S, Barr J, Banks R, Forchheimer R. Injury, pain, and prescription opioid use among former National Football League (NFL) players. Drug and Alcohol Dependence 2011;116:188–194.
Lehman E, Hein M, Baron S, Gersic C. Neurodegenerative causes of death among retired National Football League players. Neurology 2012;79:1970–1974.
Miller H. Mental sequelae of head injury. Proceedings of the Royal Society of Medicine 1966;59:257–261.
Weir D, Jackson J, Sonega A. Study of retired NFL players. Ann Arbor, MI: University of Michigan Institute for Social Research; 2009.
Topic: Are all these football players' anger issues a result of head trauma? (Read 8724 times)