About a decade ago, a great number of former NFL players filed civil and industrial injury claims in California alleging that sport related head trauma and concussions while engaged in professional football resulted in the development of a Alzheimer’s like dementia decades later. At the time, this medical condition became known as CTE or Chronic Traumatic Encephalopathy.

Their claims were based, in part, on the work of Anne McKee M.D. who is a neuropathologist and expert in neurodegenerative disease at the New England Veterans Affairs Medical Centers and is professor of neurology and pathology at Boston University School of Medicine and director of Boston University CTE Center, which was established in 1996 and funded by the National Institutes of Health to advance research on Alzheimer’s disease and related dementias.

In her early work published in 2009, she reviewed 48 cases of neuropathologically verified CTE recorded in the literature and document the detailed findings of CTE in 3 professional athletes, 1 football player and 2 boxers, and theorized that “Chronic traumatic encephalopathy is a neuropathologically distinct slowly progressive tauopathy with a clear environmental etiology.”

Het hypothesis received widespread media attention with the arrival of the movie “Concussion” a 2015 American biographical sports drama film. Will Smith starred as Dr. Bennet Omalu, a forensic pathologist who fights against the National Football League trying to suppress his research on chronic traumatic encephalopathy (CTE).

Over the years, much scientific debate ensued over her theory, and the relationship between a head trauma and the development of CTE many years later. And for over two decades, the Concussion in Sport Group (CISG) has held meetings and developed five international statements on concussion in sport.  CISG is an international multidisciplinary group of experts who work to improve the understanding and management of concussion in sport. It was founded in 2001 and has met every four years since then to produce consensus statements on the latest evidence about concussion in sport.

The CISG is made up of experts from a variety of disciplines, including neurology, neurosurgery, sports medicine, neuropsychology, and epidemiology. The group’s work is supported by the International Olympic Committee (IOC) and the World Health Organization (WHO).

The 4th Consensus Statement on Concussion in Sport published in the British Journal of Sports Medicine in 2013, reviewed the medical literature at the time and rejected the blanket conclusion that there is a definitive cause and effect connection between repetitive head trauma and CTE. It concluded that ‘the speculation that repeated concussion or subconcussive impacts cause CTE remains unproven,“

The sixth International Consensus Conference on Concussion in Sport was delayed because of the pandemic, and was rescheduled to meet in Amsterdam on 27 October 2022 through 29 October 2022. As a result of this newest Conference, the Consensus statement on concussion in sport: the 6th International Conference on Concussion in Sport – Amsterdam, October 2022 was published in the British Journal of Sports Medicine on June 14, 2023. It was compiled by 114 co-authors.

It first noted that “To avoid conceptual confusion between the pathology and a possible clinical condition, the postmortem neuropathology is referred to as CTE neuropathologic change (CTE-NC).” However “CTE-NC is not a clinical diagnosis. The first consensus criteria for traumatic encephalopathy syndrome (TES), a new clinical diagnosis, were published in 2021.

Using these new terms, CISG then wrote “These diagnostic criteria can be used to determine the extent to which CTE-NC identified after death was associated with this new clinical diagnosis during life. The prevalence of CTE-NC (a neuropathological entity) and TES (a clinical diagnosis) in former athletes, military veterans and people from the general population is not known. It is also not known whether (1) CTE-NC causes specific neurological or psychiatric problems, (2) the extent to which CTE-NC can be clearly identified within the presence of Alzheimer’s disease neuropathology or (3) whether CTE-NC is inevitably progressive.”

Critiques of the latest Consensus Conference were immediate. According to an article in Nature, “Their refusal to acknowledge a causal relationship between contact-sports participation and CTE [chronic traumatic encephalopathy] is a danger to the public,” said Chris Nowinski, a neuroscientist and chief executive of the Concussion Legacy Foundation in Middletown, Delaware, which supports athletes and veterans affected by concussions and CTE.

Yet Robert Cantu M.D. one of the co-authors of the consensus report and colleague of Ann McGee M.D. at the Boston University School of Medicine in Massachusetts said  “The CTE literature is almost exclusively case series studies” and he went on to say “And that literature did not meet the inclusion criteria for the systematic review.”