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Review strengthens evidence that repetitive head impacts can cause chronic traumatic encephalopathy

During the past 17 years, there has been a remarkable increase in scientific research concerning chronic traumatic encephalopathy (CTE) with researchers at the BU CTE Center at the forefront. While some sports organizations like the National Hockey League and World Rugby still claim their sports do not cause chronic traumatic encephalopathy, a new review of the evidence by the world’s leading chronic traumatic encephalopathy expert strengthens the case that repetitive head impact exposure is the chief risk factor for the condition.

Chronic traumatic encephalopathy became national news in the United States in 2007, but it wasn’t until 2016 that the National Institute of Neurological Disorders and Stroke/National Institute of Biomedical Imaging and Bioengineering (NINDS-NIBIB) criteria for the neuropathological diagnosis of chronic traumatic encephalopathy were published, and they were refined in 2021. Rare, isolated case studies reporting aberrant findings or using non-accepted diagnostic criteria have been disproportionately emphasized to cast doubt on the connection between repetitive head impact and chronic traumatic encephalopathy.

In a review article in the journal Acta Neuropathologica, Ann McKee MD, chief of neuropathology at VA Boston Healthcare System and director of the BU CTE Center, stresses that now over 600 chronic traumatic encephalopathy cases have been published in the literature from multiple international research groups. And of those over 600 cases, 97% have confirmed exposure to repetitive head impact, primarily through contact and collision sports. Chronic traumatic encephalopathy has been diagnosed in amateur and professional athletes, including athletes from American, Canadian, and Australian football, rugby union, rugby league, soccer, ice hockey, bull-riding, wrestling, mixed-martial arts, and boxing.

What’s more, 82% (14 of the 17) of the purported chronic traumatic encephalopathy cases that occurred in the absence of repetitive head impact, where up-to-date criteria were used, the study authors disclosed that families were never asked what sports the decedent played.

According to the researchers, despite global efforts to find chronic traumatic encephalopathy in the absence of contact sport participation or repetitive head impact exposure, it appears to be extraordinarily rare, if it exists at all. “In studies of community brain banks, chronic traumatic encephalopathy has been seen in 0% to 3% of cases, and where the information is available, positive cases were exposed to brain injuries or repetitive head impact. In contrast, chronic traumatic encephalopathy is the most common neurodegenerative disease diagnosis in contact and collision sport athletes in brain banks around the world. A strong dose response relationship is perhaps the strongest evidence that repetitive head impact is causing chronic traumatic encephalopathy in athletes,” she added.

“The review presents the timeline for the development of neuropathological criteria for the diagnosis of chronic traumatic encephalopathy which was begun nearly 100 years ago by pathologist Harrison Martland who introduced the term "punch-drunk” to describe a neurological condition in prizefighters,” explained McKee, corresponding author of the study. The review chronologically describes the multiple studies conducted by independent, international groups investigating different populations that found chronic traumatic encephalopathy pathology in individuals with a history of repetitive head impact from various sources.”

Chronic traumatic encephalopathy is characterized by a distinctive molecular structural configuration of p-tau fibrils that is unlike the changes observed with aging, Alzheimer disease, or any other diseases caused by tau protein.

Source: News Release
Boston University School of Medicine
February 10, 2023

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