cte: what we don’t know

Sunday, July 31, 2016

The press has not been kind to Gary Bettman this week and this time, the press is wrong. The NHL Commissioner wrote a letter in response to questions asked by Connecticut Senator, Richard Blumenthal, that outlined the league’s position regarding concussion and the long term effects of head injury. The New York Times called out his “reluctance to link hits to the head in hockey with a degenerative brain disease”.  Sports Illustrated wrote of the “refusal to acknowledge a possible link between concussions and CTE has proved to be controversial.”

“I was surprised and appalled, because I thought the response would be more receptive,” Blumenthal told SI.com via telephone from Philadelphia. “I would’ve welcomed an acknowledgement for stronger action and a commitment to determining whether the game is causing these heartrending injuries with such painful consequences, rather than dismissing the link between hockey and CTE.” 

Mr. Bettman’s 24-page letter acknowledged the potential for head injury and concussion in all contact sports and also summarized the medical literature that has yet to prove that chronic traumatic encephalopathy (CTE) is caused by concussion. While it seems intuitive that CTE is caused by trauma, there are major questions that remain unanswered.

Association v. Causation

There is no doubt that there is an association between traumatic brain injury and CTE, but the research is just beginning as to what causes some people to develop CTE and others to be spared. Or have they been? With todays’ science and technology, CTE can only be diagnosed after death by autopsy, and then only if the brain is dissected and special stains are used to look at cells under the microscope. Of the athletes whose brains have been studied, there seems to be a correlation between the many concussions that they had sustained and CTE findings in the lab. Unfortunately, there is a problem with the statistics.

For a cause and effect to be found, brains from different groups of athletes need to be studied:

  • Those who had no concussion history and no signs or symptoms of depression or dementia
  • Those who had no concussion history but developed signs or symptoms of depression or dementia
  • Those who had a concussion history and had no signs or symptoms of depression or dementia.

As of now, researchers have mostly studied those who have had a history of concussion and developed signs of mental illness and/or dementia.

What do we know?

There is evidence that there is a link exists between a severe traumatic brain injury and the eventual development of dementia. There also may be a dose relationship, meaning the more severe the head injury, the more likely dementia becomes a future possibility.  However, there is not necessarily that same link that connects repetitive minor head injuries with CTE. Lots of small concussions does not necessarily equal one major head injury.

…specifically for rTBI (recurrent mild traumatic brain injury), there has been an unavoidable case-selection bias and a virtual absence of control material from uninjured cases in reports of CTE, rendering interpretations of the incidence of this pathology meaningless in the context of exposure to repetitive mild injury. –  Hay J, et al. Annual Review of Pathology. May 2016

While the public is hearing about brain chemistry and anatomy, including tau proteins and neurofibrillary tangles, other research is ongoing looking at other markers of brain injury. These include amyloid deposits, DNA binding proteins, neuroinflammtion, brain white matter degradation and neuron (brain cell) loss. Chromosome research may offer some clues to CTE development, with certain genes more likely to be associated  CTE after a brain injury and others that might injure the brain by activating certain enzymes. 

What don’t we know?

Traumatic brain injury is known to be the biggest risk factor for developing dementia. The question is how much brain trauma is needed to cause CTE.

  • Does it take one or multiple concussions?
  • Are concussions spaced closer together more dangerous? Or does the same damage occur even when they are spaced years apart.
  • Is concussion in children and teenagers more important than later in life? or are their brains better able to adapt and heal themselves?
  • Do brains heal themselves and become pristine after a period of time, or is the concussion damage permanent?
  • Why do some concussion patients develop depression and dementia, while other do not?

The bottom line is that while a relationship exists between head injury and degenerative brain disease, scientific research has yet to prove that concussion causes CTE. There are many next steps for research to take, including being able to diagnose CTE in live patients without having to wait until they die to perform an autopsy. For now, we know that we don’t know a lot.

There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don’t know. But there are also unknown unknowns. There are things we don’t know we don’t know. – Donald Rumsfeld.


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