What Do We Know About How Many People Might Have CTE?

Prevalence is a very difficult study to perform when we don’t have a diagnostic marker during life. I think once we have that diagnostic marker we’ll be able to do prevalence studies fairly easily. But at this point we can only make the diagnosis after death. So for us to do a really well-composed prevalence study, we’d have to get two groups with different exposures to football and follow them till death some 60 years and then look at the rates of CTE in their brain after death. So nobody has 60, 70 years to wait until this answer. So what we have is a convenience sample. It’s a brain bank sample. It does have selection bias in it. There’s no question. But all brain bank studies have selection bias. It’s important to know that in our brain bank, the criteria for admission to the brain bank is based on exposure to head injury. We don’t look for symptoms. We don’t look for anything else. It’s just whether or not they were exposed to head injury. That’s not true for any other brain bank that I know of. This is a unique brain bank. In all of those other brain banks, CTE is very rare. The ones that don’t recruit for head injury. But in our brain bank, it’s very high. In fact, in our JAMA study that came out last July it was 87% for all American football players over an eight-year period, which is quite high. Now, a lot of what I would say people that don’t want to accept CTE as a real public health issue. They have pointed to that selection bias as a reason to discredit the study, a reason to just ignore the study altogether. And I think that’s quite ridiculous. First of all, we do have selection bias. But the people that ask for the brain to be examined, because 90% of our brains come from the families of the person, not from a doctor or from a medical examiner. They come from the families. Those people are ordinary citizens. They’re not specifically trained as diagnosticians. They don’t have a tertiary medical center in their back pocket. They haven’t done all sorts of fancy tests. These are just people that have seen the symptoms, thought something was unusual usually, and had a hunch that something was going on. And they referred the brain in for us to analyze it. And so that hunch is 87% correct. That’s remarkable. So that just wouldn’t happen unless this is a real problem. We don’t know the degree of that public health problem, but it’s certainly an issue. And if we look at the denominator just in NFL players because we had 111 NFL players in that study. If we took all the NFL players that died during an eight-year period that were included, if we assume that every other NFL player that died somewhere else that didn’t donate their brain to science did not have CTE, which would be a very absurd assumption. The minimum rate of NFL players being affected is 10%. That’s the least it could possibly be. And so you have to ask yourself: is that an acceptable occupational hazard that 10% of you are gonna develop an untreatable, progressive neurodegenerative disease. So, in my mind that’s clear evidence that this is an issue. And then there were a lot of amateur players in that study. 91% of the college players, 21% of the high school players were diagnosed with CTE. So this isn’t just something that happens to the extreme and extraordinarily gifted football players. This is something that happens to amateurs. This video was produced by BrainLine thanks to generous support from the Infinite Hero Foundation.
Posted on BrainLine December 20, 2018.

About the author: Ann McKee, MD

Ann McKee, MD is the chief neuropathologist for the Framingham Heart Study and the Boston University-based Centenarian Study. She is also the chief neuropathologist for the Boston-based Veterans Administration Medical Centers and for the Sports Legacy Institute.

Ann McKee