Does CTE Cause Aggression? Study Finds Link to Dementia Instead

Last year, a gunman opened fire in a New York City office building intending to target the National Football League’s offices for allegedly concealing the dangers of repeated head injuries. The shooter, a former football player, believed he had chronic traumatic encephalopathy (CTE), a disease caused by brain trauma linked to memory loss, cognitive decline, and behavioral changes like aggression. 

The incident reignited questions and CTE experts say reignited debate about links between CTE and violent behavior. 

Researchers at Boston University’s CTE Center are studying hundreds of donated brains to better understand the disease. Currently CTE can’t be diagnosed in living people, and researchers disagree on whether it leads to progressive neurodegeneration and dementia. In his recent study published in the journal Alzheimer’s & Dementia, co-director Michael Alosco hoped to clarify these links

The study found no link between CTE and mood or behavioral changes like aggression, which are often emphasized in media coverage, but did find an increased risk for dementia. Alosco told Being Patient the strength of the association was comparable to the link between Alzheimer’s-related proteins and symptoms. 

However, because of the study’s limitations, Dr. Rebecca Folkerth, neuropathologist at the Icahn School of Medicine at Mount Sinai who wasn’t involved in the study, cautions it doesn’t make a clear-cut case that CTE leads to dementia. 

Searching for the link between CTE and dementia

Alosco and his team autopsied the brains of 248 donors with the pathology or hallmark protein plaques of CTE and 366 without. Almost 97 percent of the study participants were men, more than 80 percent were white, and many were football players. The sample wasn’t representative of the general population or the football community, which includes a higher proportion of Black athletes. 

“What was novel about this study is that we excluded everyone who had another major progressive brain disease,” Alosco said. 

By excluding people whose brains had signs of Alzheimer’s and many other neurodegenerative conditions, they could more specifically test whether CTE was linked to cognitive and behavioral symptoms.

But participants with TDP-43 protein aggregates and other brain features indicative of LATE dementia, as well as those with vascular problems that could contribute to cognitive decline were not excluded, which Folkerth said, would make it difficult to say whether CTE is the only factor contributing to symptoms. 

The researchers grouped, or staged, each brain from zero to four based on the levels of abnormal tau proteins in the brain. Early stages were not linked to cognitive symptoms or a dementia diagnosis, but those in stage three or four had a higher likelihood of reporting memory and thinking problems or receiving a dementia diagnosis. 

“The staging system has not been externally validated by any group outside of Boston University,” said Folkerth. She also pointed to the fact that those in the later stages of CTE identified by the authors were also older, which could contribute to the cognitive symptoms. 

Although in media coverage, CTE is often associated with mood and behavioral problems, this study found no relationship between those symptoms and CTE.

Many individuals in the study may have been misdiagnosed. Nearly 40 percent were incorrectly diagnosed with Alzheimer’s, Alosco said. “It really emphasizes the need for clinicians to assess and consider exposure to head trauma when they’re making diagnoses and managing care,” he said.

Folkerth, on the other hand, isn’t convinced that these links are clear-cut and doesn’t think the study shuts the door on the question. 

What’s next for CTE? 

Even though repetitive head trauma may be a risk factor for dementia, it isn’t inevitable. 

“We should also be careful not to also assume that you’re going to go down that path no matter what,” said Alosco. “If you’re noticing thinking and memory problems, get into a neurology clinic to get it checked out.”

Researchers are still grappling with many questions about CTE. It isn’t clear what the “tipping point” where tau buildup in CTE causes symptoms. “This is the million dollar question,” said Folkerth. 

She worries that people with multiple head injuries might start to worry they have a fatal, progressive disorder, even though it’s not yet certain that’s the case with CTE.

Neuropathologists later uncovered that the Manhattan shooter had early-stage CTE, but this study adds evidence that mood and behavioral symptoms may not be direct consequences. “People were so quick to ascribe his behavior to the fact that he had stage two CTE” Folkerth said, “that they stopped looking at other treatable causes.”