Almost all cases of chronic traumatic encephalopathy (CTE) analysed through research are linked to exposure to repetitive head impact, primarily as a result of contact and collision sports, a groundbreaking new study has discovered.
Over 600 cases of CTE have been published in literature from multiple international research groups – and 97 per cent of those have confirmed exposure to repetitive head impact (RHI).
And of the 14 of the 17 purported CTE cases that occurred in the absence of RHI, where up-to-date criteria were used, the study authors found that families were never asked what sports the individual played.
The review of research – led by Dr Ann McKee, director of the BU CTE Center and world-leading authority on CTE – confirms that, despite global efforts to find CTE in the absence of contact sport participation or RHI exposure, it appears to be extremely rare – if it exists at all.
“In studies of community brain banks, CTE has been seen in zero to three per cent of cases, and where the information is available, positive cases were exposed to brain injuries or RHI,” says Dr McKee.
“In contrast, CTE 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 RHI is causing CTE in athletes.”
CTE has been subject to a significant increase in scientific research over the past 17 years, primarily led by researchers at the BU CTE Center, but despite mounting evidence of the link between RHI and neurodegenerative disease, criticism has been made of sports bodies for not taking action to protect players quickly enough.
CTE became national news in the United States in 2007, but it was not 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 CTE were published, and they were refined in 2021.
CTE has been diagnosed in amateur and professional athletes, including those who took part in football, rugby union, rugby league, American football, ice hockey, bull-riding, wrestling, mixed-martial arts, and boxing.
The research continues to make advances in knowledge around CTE. While it cannot yet be diagnosed during life, evidence is showing that MRI may show the disease in the living.
It is hoped the new review of research to date will help to increase the prevalence of CTE in looking at the impact of RHI, particularly in sport, and to encourage governing bodies to take action, with aims being set out to find a cure for CTE by 2040.
“The review presents the timeline for the development of neuropathological criteria for the diagnosis of CTE 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 Dr McKee.
“The review chronologically describes the multiple studies conducted by independent, international groups investigating different populations that found CTE pathology in individuals with a history of RHI from various sources.”
