Head Trauma Strongly Linked To Chronic Traumatic Encephalopathy But Precise Relationship Not Yet Known
Causal link ‘scientifically premature’
Similarly, the absence of cross-sectional, epidemiological, prospective or longitudinal studies on CTE has led many of the most respected experts and researchers in the concussion community to express caution in quantifying the risk of CTE posed by repetitive head impacts, although, again, that fact, with some notable exceptions, has not been widely reported by the media.
An exception was a recent article in which a leading concussion researcher, Dr. Michael McCrea (a member of the scientific panel for the upcoming Berlin conference), singled out for criticism a statement by Dr. McKee in the PBS Frontline documentary League of Denial in which she said she was “really wondering if every single football player doesn’t have [CTE].”
“This is one of those situations where the story has really raced out in front of the science,” McCrea told a reporter for the Milwaukee Business Journal. He agreed that concussion is a serious injury and the sports industry should take it seriously. But McCrea had a problem with League of Denial using what he considered speculation that has yet to be proven in clinical research
In an article in the online publication Deadspin (32), Matthew McCarthy, a physician at New York-Presbyterian Hospital, writes about the “puddles of ink” that will be “spilled linking head trauma to chronic traumatic encephalopathy … written by sportswriters who, frankly, don’t understand the science and have long overstated what is actually known about the condition.”
About the Zurich statement’s conclusion that no cause and effect relationship had been demonstrated, Dr. McCarthy points out that the statement “runs counter to almost everything you have read about CTE, but it received virtually no media attention in the United States when it was released. In part, that’s because it speaks to the far higher burden of proof in the scientific community than the one in the public consciousness. But that’s the point. The popular consensus has far outstripped the science.”
As for Dr. McKee’s statement to NewJersey.com, McCarthy observes that she argued that, while there was not scientific proof, there was enough to start thinking about making changes, so she “and others have chosen to bang the drum, loudly, even if they can’t be sure of the exact message once we’re listening.” (the fact, of course, is that changes are being made, most notably in the form of limits on full-contact practices)
In their 2013 meta-analysis of the scientific literature on CTE (19) Gardner, and two highly respected colleagues, Grant Iverson and Paul McCrory (the lead author of the last three international consensus statements on sport-related concussion, including the 2013 Zurich statement that prompted such expressions of outrage by McKee and Cantu, and a member of both the organizing and scientific committee for the 5th international concussion conference scheduled for Berlin) (13)) characterized the “strongly presented causal assumptions in the literature relating to concussive and subconcussive brain impact exposure” as “scientifically premature.”
In order to reach that conclusion, writes Gardner, systematic research is needed to address five specific unanswered questions:
First, it is not known whether similar, or even identical, neuropathological findings are observed in other samples that share clinical characteristics with CTE such as patients with drug or steroid abuse, alcohol abuse histories, chronic psychiatric problems, cardiovascular/cerebrovascular disease or other health conditions. (although it should be noted here that a 2015 meta-analysis of all reported cases of CTE (68) appears to suggest otherwise, finding no evidence to link substance abuse, genetic factors, such as APOE or pre-existing medical conditions, to an increased risk of CTE).
Second, the extent to which the reported underlying neuropathology contributes to the reported clinical features (eg, cognitive deficits, psychiatric features) is uncertain.
Third, the potential existence of a genetic contribution to the observed neuropathology has not been determined. (Again, the 2015 meta-analysis of CTE cases (68) found no evidence to support the view that genetic factors increased risk of CTE]
Fourth, possible mediator or moderator variables for the association between the neuropathology and the clinical features have not been identified
Finally, noted Gardner, “we do not have a methodology for identifying individuals who are at future risk or might currently have CTE. Psychiatric problems and cognitive impairment usually have multifactorial, not unitary causation – this will require further attention in future studies. The important next step in the process of potentially answering some of the unresolved issues associated with CTE is to conduct large-scale, prospective, longitudinal, clinicopathological studies.”
To be fair, both Drs. Cantu and McKee have also called for such studies, as have many others (67), and such research is beginning, with the NCAA beginning a long-term study, and Stern leading a multi-site study of CTE under a grant from the National Institutes of Health. Dr. Cantu, in a moment of honest and candid reflection on the impact he has as a leading authority on concussions, acknowledged in a postscript to the paperback edition of his 2012 book, Concussions and Our Kids (44), that if there was “one thing that isn’t explained as fully in the book as [he] wish[ed] … it is the precise relationship between total head trauma (concussions and also subconcussive blows) that a child absorbs playing football and hockey and, to a lesser degree, soccer and basketball and the possibility of developing a degenerative brain disease such as CTE as an adult. We don’t know yet,” he admits. “The research continues, and it is possible that we will have an answer to that critical question soon, perhaps with a decade.”
Real world consequences
But, in the meantime, it appears that the prevailing narrative – at least in the mainstream media and among pundits and commentators – is that those that play contact and collision sports in general, and football in particular, and youth football even more specifically, are at serious and high risk of developing a frightening, degenerative, irreversible disease, when, as noted by Dr. McCarthy, “the study of head injuries is a lot more confusing and murky than once suspected.”
The media narrative, argues Dr. McCarthy, has real world consequences in which former NFL players, and all those who ever donned a football helmet, may be, to a greater or lesser degree, “collateral damage.”
As he points out in his gripping first person account of an encounter with an unidentified former NFL player in the psychiatric ward of a New York hospital, the former player was paralyzed by the fear that he was “walking around with a death sentence over [his] head.”
“An aging athlete,” he argued, should not have to “assume that a neurologic symptom is from CTE or that his life is about to unravel. There may be an alternate treatable explanation. And, either way, a physician should be making the diagnosis,” not a journalist or even a research scientist.