Open Letter: The available evidence demands the relationship between RHI and CTE should only be described as causal

Tuesday, September 13, 2022

Open Letter: The available evidence demands the relationship between RHI and CTE should only be described as causal

To Whom it May Concern:

As scientists, physicians, researchers, and public health experts, we believe the relationship between repetitive head impacts (RHI) and chronic traumatic encephalopathy (CTE) should no longer be referred to as an ‘association’. Rather, we believe that the available evidence demands the relationship between RHI and CTE should only be described as causal.

We respectfully request your organization update all position papers and public-facing statements to reflect the current scientific understanding in an urgent effort to educate the public.

As you consider this request, we ask that you review a recently published analysis of the evidence for RHI causality in CTE using the Bradford Hill criteria. The Hill criteria were created specifically to provide a methodology for reviewing epidemiologic research to determine when it is appropriate to move from labeling an observed relationship as an association to causation.

The review, entitled Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and CTE, was published Frontiers in Neurology on July 22. The evidence for causation has strengthened considerably in the last few years, specifically in strength of association, biological gradient, consistency, plausibility, and coherence.

The authors conclude that the evidence in favor of RHI as a causal pathway leading to CTE is compelling enough to move from “association” to “causation.” We agree with this conclusion, and we support creating policies to prevent CTE in the next generation of contact sport athletes and others exposed to repetitive head impacts.

We recognize that RHI may someday be found to not be the only risk factor or precipitant to CTE, as many diseases have multiple causes. However, it is time to publicly acknowledge that RHI is a causative factor which can lead to CTE.

In August, we petitioned the National Institute of Neurological Disorders and Stroke (NINDS) to review this evidence and update their statement on causation. On October 5, 2022, NINDS updated their official statement on CTE to “CTE is a delayed neurodegenerative disorder that was initially identified in postmortem brains and, research-to-date suggests, is caused in part by repeated traumatic brain injuries.”

To many, this is not new information. The idea that boxing causes progressive neurodegeneration has been widely accepted for nearly a century. In 2019, the U.S. Centers for Disease Control and Prevention (CDC) issued a fact sheet, stating, “The research to-date suggests that CTE is caused in part by repeated traumatic brain injuries, including concussions, and repeated hits to the head, called subconcussive head impacts.”

Besides NINDS and CDC, organizations that now utilize or publicly support causation language include the NFL in the United States, the National Health Service, Football Association, and Professional Footballer’s Association in the United Kingdom, and the Australian Football League.

We have created an online dashboard listing organizations that recognize the role of RHI and rTBI in CTE causation, and we also list organizations that explicitly do not or have not made public statements. Please let us know if we do not have your organization listed appropriately.

We look forward to your response and are available individually or as a group to respond to any questions you may have.

Signed,

• Mike Alosco, PhD - Associate Professor of Neurology, Co-director, Alzheimer’s Disease Center Clinical Research Core, Principal Investigator, CTE Center, Boston University School of Medicine
• Breton Asken, PhD, ATC - Assistant Professor, Department of Clinical and Health Technology, University of Florida, Fixel Institute for Neurological Diseases
• Rhoda Au, PhD - Professor of Anatomy & Neurobiology, Neurology and Epidemiology, Boston University Schools of Medicine and Public Health
• Kathleen Bachynski, PhD, MPH - Assistant Professor of Public Health, Muhlenberg College
• Kevin Bieniek, PhD - Director, Glenn Biggs Institute for Alzheimer’s & Neurodegenerative Diseases Brain Bank, Neuropathology Core Leader, South Texas Alzheimer’s Disease Research Center, Assistant Professor, Department of Pathology & Laboratory Medicine, University of Texas Health Science Center at San Antonio
• Charles Bernick, MD, MPH - Clinical Professor of Neurology, University of Washington
• Yelena Bogdanova, PhD - Assistant Professor of Psychiatry, Boston University School of Medicine
• Michael Buckland, MBBS, PhD, FRCPA, FFSc (RCPA) - Clinical Associate Professor of Pathology, School of Medical Sciences, University of Sydney, Head of the Department of Neuropathology at Royal Prince Alfred Hospital, Founding & Executive Director, Australian Sports Brain Bank
• Samantha Bureau, PhD - Director of Programs, Concussion Legacy Foundation
• Robert Cantu, MD, MA, FACS, FAANS, FICS, FACSM - Clinical Professor of Neurology, Boston University School of Medicine
• Stephen T. Casper, PhD - Professor, Humanities and Social Sciences, Clarkson University
• David X. Cifu, MD - Associate Dean of Innovation and System Integration and Eminent Scholar, Herman J. Flax, MD Professor and Chair, Department of Physical Medicine and Rehabilitation, Senior Consultant, Sheltering Arms Institute, Virginia Commonwealth University School of Medicine
• John F. Crary, MD, PhD - Professor, Director, Neuropathology Brain Bank & Research Core, Icahn School of Medicine at Mount Sinai
• Jeffrey L. Cummings, MD, ScD - Joy Chambers-Grundy Professor of Brain Science, Director, Chambers-Grundy Center for Transformative Neuroscience, University of Nevada Las Vegas (UNLV)
• Maurice Curtis, PhD - Professor of Neuroscience, Head of Department, Anatomy and Medical Imaging, The University of Auckland
• Daniel Daneshvar, MD, PhD - Assistant Professor, Assistant Chair for Research, Department of PM&R, Harvard Medical School
• Steven T. DeKosky, MD, FACP, FANA, FAAN - Deputy Director, McKnight Brain Institute, Professor of Neurology and Neuroscience, University of Florida
• Marc Diamond, MD - Director, Center for Alzheimer’s and Neurodegenerative Diseases, Professor of Neurology and Neuroscience, University of Texas, Southwestern Medical Center
• Ramon R. Diaz-Arrastia, MD, PhD - Director of Traumatic Brain Injury Clinical Research Center, University of Pennsylvania Perelman School of Medicine
• Dennis W. Dickson, MD - Robert E. Jacoby Professor of Alzheimer’s Research, Mayo Clinic
• David W. Dodick, MD - Professor Emeritus, Mayo Clinic Arizona, Chair, International Concussion Society
• Margaret Esiri, DM, FRCPath - Emeritus Professor of Neuropathology, Oxford University
• Sir Richard Faull, MBCHB, DSc, KNZM, FRSNZ - University Distinguished Professor, Director, Centre for Brain Research, The University of Auckland
• Adam M. Finkel, ScD, CIH - Clinical Professor of Environmental Health Sciences, University of Michigan School of Public Health
• Sam Gandy, MD, PhD - Professor of Neurology and of Psychiatry, Icahn School of Medicine at Mount Sinai
• Lee E. Goldstein, MD, PhD - Associate Professor, Boston University School of Medicine & College of Engineering
• Michael J. Grey, PhD - Reader in Rehabilitation Neuroscience, University of East Anglia
• Lea T. Grinberg, MD, PhD - Professor in Residence, Departments of Neurology and Pathology, UCSF
• Elisa Hill-Yardin, PhD - Associate Professor, Royal Melbourne Institute of Technology
• Sidney R. Hinds II, MD, FAAN - COL (retired), United States Army, Assistant Professor, Neurology/Radiology, Uniformed Services University
• Kenneth S. Kosik, MD - Hariman Distinguished Professor of Neuroscience, Co-Director, Neuroscience Research Institute, Santa Barbara, CA
• Chester Mathis, PhD - Distinguished Professor of Radiology, University of Pittsburgh
• Ann McKee, MD - William Fairfield Warren Distinguished Professor of Neurology and Pathology, Boston University, Chief, Neuropathology VA Boston
• Jesse Mez, MD - Associate Professor of Neurology, Boston University School of Medicine
• Michael D. McClean, ScD - Professor of Environmental Health, Boston University School of Public Health
• Bruce Miller, MD - Director, Memory and Aging Center, University of California, San Francisco (UCSF)
• Helen Murray, PhD - Research Fellow, Centre for Brain Research, The University of Auckland
• Christopher Nowinski, PhD - CEO, Concussion Legacy Foundation
• Alan Pearce, PhD - Research Manager, Australian Sports Brain Bank (Victoria), Adjunct Associate Professor, La Trobe University
• Gil Rabinovici, MD - Director, UCSF Alzheimer’s Disease Research Center, UCSF
• Philip Schatz, PhD - Professor of Psychology, Saint Joseph’s University
• Julie Stamm, PhD, ATC - Clinical Assistant Professor, University of Wisconsin-Madison
• Judith A. Steen, PhD - Director of the Neuroproteomics Laboratory, Boston Children’s Hospital, Harvard Medical School
• Thor D. Stein, MD, PhD - Associate Professor of Pathology & Laboratory Medicine, Boston University School of Medicine
• Robert Stern, PhD - Professor of Neurology, Neurosurgery, and Anatomy & Neurobiology, Boston University School of Medicine
• Michael J. Stuart, MD - Professor, Department of Orthopedics and Sports Medicine, Mayo Clinic
• Catherine Suter, PhD - Chief Scientist, Australia Sports Brain Bank
• Carmela Tartaglia, MD, FRCPC - Associate Professor, University of Toronto, Co-director Memory Clinic – Toronto Western Hospital
• Charles H. Tator, OC, MD, PhD, FRCSC, FACS - Professor of Neurosurgery, University of Toronto, Director, Canadian Concussion Centre
• Neil Vasdev, PhD - Azrieli Endowed Chair in Brain and Behaviour, Professor, Department of Psychiatry, University of Toronto
• Jennifer Weuve, MPH, ScD - Associate Professor, Department of Epidemiology, Boston University School of Public Health
• Adam White, PhD - Senior Lecturer in Sport & Coaching Sciences, Oxford Brookes University
• Kristine Yaffe, MD - Professor of Psychiatry, Neurology and Epidemiology, UCSF School of Medicine

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