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Dr. Ann McKee: We have no idea what percentage of NFL players develop CTE

Football Brain Disease

This combination of PET scans provided by UCLA on April 2, 2015 shows, from left, a normal brain scan, a suspected Chronic Traumatic Encephalopathy (CTE) subject, and a subject with Alzheimer’s disease. In a report released on Monday, April 6, 2015, researchers say this brain-scanning technique might one day help doctors identify people with CTE, a disease linked to concussions in football and other sports, an illness now diagnosed after death. Symptoms include memory loss, confusion, aggression, depression and progressive dementia. These images are from the article “In vivo Characterization of Chronic Traumatic Encephalopathy (CTE) using [F-18]FDDNP-PET Brain Imaging,” first author Jorge R. Barrio. (AP Photo/PNAS/David Geffen School of Medicine at UCLA)


Researchers in Boston studying the brains of deceased NFL players have found chronic traumatic encephalopathy, or CTE, in more than 90 percent of them. That has led some to assume that more than 90 percent of NFL players develop CTE -- a conclusion not supported by the science.

Because researchers have studied the brains only of players who asked to have their brains studied -- or whose families asked for their brains to be studied -- the sample is biased. A randomly selected sample of NFL players’ brains would need to be compared to a randomly selected sample of non-NFL players’ brains for researchers to reach any kind of conclusion about the prevalence of CTE among NFL players compared to the prevalence of CTE among the population as a whole. So far, that kind of study has not been conducted.

Dr. Ann McKee, the chief of neuropathology at the V.A. Boston Healthcare System and a professor of neurology and pathology at Boston University’s medical school, was the researcher who gave a presentation before Congress that preceded NFL executive vice president Jeff Miller’s declaration that there is “certainly” a link between football and CTE. But McKee acknowledges that she doesn’t know -- no one knows -- what percentage of players develop CTE.

“We can’t say from this sample whether the rate of CTE in pro players is 1 percent or what; we have no idea,” McKee told the New York Times.

McKee said that she doesn’t think CTE is rare among NFL players because it would be unlikely that she would see it in such a large percentage of the brains she studies if it were unusual in NFL players overall. But she doesn’t know for sure.

“I don’t think it’s extremely rare. I would have to have some golden touch to see this many, if it were,” McKee said.

Robert Stern, a professor of neurology and neurosurgery at the Boston University School of Medicine, who works with McKee, added that “This research is in its infancy.”

Much more research needs to be done.