Head Trauma Strongly Linked To Chronic Traumatic Encephalopathy But Precise Relationship Not Yet Known
“The interpretation of causation in the modern CTE case studies should proceed cautiously,” urges another 2013 literature review (22) whose authors not only include McCrory and Gardner, but such pre-eminent concussion researchers as Willem H. Meeuwisse of the University of Alberta (another member of the organizing and scientific committees for the upcoming Berlin conference), and neurologist Jeffrey S. Kutcher, Director of the Sport Neurology Clinic at the Core Institute in Brighton, Michigan, co-author of the 2013 American Academy of Neurology’s concussion guidelines (23), and co-author of the new book, Back in the Game: Why Concussion Doesn’t Have To End Your Athletic Career.
Between and 2015, five reviews of the peer-reviewed literature (39-42, 73) poured cold water on the now common assumption in the media and general population that contact sports inevitably causes CTE, and that CTE causes those with the disease to commit suicide.
In the first, published in the British Journal of Sports Medicine (39) a leading concussion researcher, Grant Iverson, MD, of the Department of Physical Medicine and Rehabilitation at Harvard Medical School, found the scientific evidence insufficient to support a finding of the existence of a strong causal relationship between CTE and suicide in former athletes.
In the second, published in the journal Behavioral Sciences and the Law, (40) scientists at the University of Colorado School Medicine conducted a state-of-the-science review of CTE, explored the evidence for links between traumatic brain injury (TBI), CTE and catastrophic clinical events such as suicide, and highlighted the complexity of specifically attributing suicide to CTE. Like Iverson, they urged caution in jumping to conclusions on the basis of preliminary case study autopsies.
In the third commentary, published in the journal Neuropsychological Review (41), Randolph, the Loyola University – Chicago neuropsychologist, and, as noted earlier, the leading skeptic about the link between CTE and contact sports, reviewed the history of so-called “classic” CTE in boxers, the literature on “modern” CTE (case studies from 2005 forward), mainly in American football players, and explored the sampling and methodological issues that, he said, prevented any firm conclusions about the association between athletic head trauma and neurodegenerative diseases such as CTE being drawn, and called, like Iverson and Wortzel, for more carefully-controlled epidemiological and prospective studies to overcome current limitations in this research and stimulate further research.
Fourth, commenting in the British Journal of Sports Medicine on a systematic review of the literature on CTE in sport (19) published in the same issue of the journal, Charles Tator, MD, of the Division of Neurosurgery at the University of Toronto, while noting the “significant advances” over the past 10 years in understanding CTE that allowed the sports community to understand that the issue of brain degeneration as a consequence of repetitive concussion was not confined to boxers but applies at least to hockey, football, wrestling, and rugby, emphasized, however, that there were many questions to be answered, among them:
- the percentage of concussed athletes who will develop CTE
- the exact relationship between concussion and brain degeneration
- how many concussions are required to cause brain degeneration
- whether subconcussive blows lead to the same neurological deficits and pathological changes as concussive blows
- whether it is possible to recognize clinical precursors to CTE, such as post-concussion syndrome
- whether the changes in the brain resulting from repetitive concussions are specific to concussions or are similar to degenerative changes that occur as a result of normal aging or diseases of aging, such as Alzheimer’s, dementia, and Parkinson’s disease
- how many non-concussed athletes or non-athletes will have any of the changes in the brain, such as tau protein deposits, considered specific markers for CTE.
Like Iverson, Wortzel, and Randolph, Tator says longitudinal studies of large number of at-risk athletes are “essential.” The recent editorial in the British Journal of Sports Medicine (67) takes the same view.
Finally, in a critical review of the medical literature in 2016 (73), Iverson concluded that, while it has been asserted and assumed that suicidality and completed suicide are common clinical features of CTE, and that this belief has been reinforced in the general public and the medical and scientific community by thousands of media stories, the science underlying the assertions and assumptions that suicide is caused in whole or part by the neuropathology of CTE, or that it is a core clinical feature of CTE, is “extremely limited, inconclusive, and, in fact, contradictory” He therefore argued that “it is currently premature to assume that people with the neuropathology believed to be characteristic and unique to CTE are at an increased risk for suicide,” noting that establishing such an alleged connection will be extremely difficult given the absence of agreed-upon and validated clinical (or neuropathological) diagnostic criteria for CTE required to reliably or accurately diagnose the disease in a living person.
Causal link likely exists, just not yet proven
It is important to emphasize that such researchers are not saying that such causal links won’t ever be established. As Gardner admits, “Ultimately, scientific research might establish that participation in contact sports leads to a distinct neuropathological syndrome, and this neuropathology causes psychiatric, cognitive and physical problems.” (19)
Indeed, the authors of one recent paper (40) acknowledge that “it simply makes good clinical sense to continue practices to minimize the number of concussions sustained and that allow for adequate recovery after any concussion” while awaiting the results of such studies. The authors of the 2015 BJSM editorial on CTE (67) take the same view: “Despite uncertainties, strategies to reduce the number of concussive and subconcussive head impacts in American football [and in other sports, presumably, such as soccer, lacrosse, and hockey] should be a top priority.”
At the same time, however, they say it is “essential to avoid embracing preliminary results derived from relatively small case numbers and methodologically problematic studies as undisputed medical fact, and to allow such results to redirect clinical practice away from established standards.”
A concerted effort is thus needed, they say, to educate medical professionals and the public at large regarding the state of the science of mTBI and CTE in order to avoid “catastrophizing” mTBI, to mitigate the “collective anxiety” that has resulted, and to reduce the likelihood that outcomes after mTBI will be actually be made worse as a result of the media frenzy around CTE.