Sports-related concussion is arguably the most widely publicized topic in neurology today. The association between traumatic brain injury (TBI) and Alzheimer’s disease has been suggested and discussed in the literature for many years. Studies have shown that TBI can trigger amyloid pathways (ie, Alzheimer’s disease). Epidemiologic studies have shown an increased risk of head trauma and amyotrophic lateral sclerosis (ALS) in Italian soccer and NFL players. In 2005, Guskiewicz et al looked at the risk of a single and recurrent concussion in NFL players and the risk of developing mild cognitive impairment (MCI) and Alzheimer’s disease. Retired players with three or more concussions had a fivefold prevalence of MCI and a threefold prevalence of self-reported memory problems. There was not an association between recurrent concussion and Alzheimer’s disease.
More recently, McKee and her colleagues at the Boston University School of Medicine analyzed the brains of athletes with known and suspected multiple head impacts and mild TBI. The researchers found abnormal protein deposition (ie, tau and TDP-43), which were consistent with a pathologic diagnosis of chronic traumatic encephalopathy. They also looked at a subpopulation of patients with known and suspected ALS and found similar changes in the spinal cords of three patients.
Lehman’s study echoes the findings of the Boston University group and Guskiewicz, as well as the clinical observations by this author and other sports neurologists that former professional athletes who participated in high-impact contact sports are beginning to show signs of dementia in their forties and fifties. As the authors acknowledged, it is difficult to determine any causality between high-velocity head impacts and subconcussive events and the neurodegenerative disorders reported in these athletes. The authors were unable to correlate their data with the actual number of concussive and/or subconcussive events.
In addition, the accuracy of the reported neurodegenerative disorders may be in question. Alzheimer’s disease is often a listed diagnosis in patients with vascular associated dementia, and Parkinson’s disease may actually be essential tremor or Parkinsonism.
One of the more interesting aspects of the study’s design is the comparison of the speed versus nonspeed positions. The NFL looked at the risk of a single and repeated concussion in two separate papers, and the relative risk for a single concussion was highest at the skill and speed positions (quarterback, wide receiver, tight end, and defensive backs), while the defensive secondary, kick unit, running backs, and linebackers had the highest risk of repeat concussions. This correlates with the study’s findings of a higher incidence of neurodegenerative disease in the speed positions.
Further longitudinal studies (and funding for such studies) into the long-term effects of single, multiple, and subconcussive events as a long-term risk of neurodegenerative disease are needed.
—Francis Xavier Conidi, DO, MS
Director of the Florida Center for Headache and Sports Neurology
Team Neurologist for the NHL’s Florida Panthers
Assistant Clinical Professor of Neurology at Florida State University School of Medicine
Guskiewicz KM, Marshall SW, Bailes J, et al. Association between recurrent concussion and late-life cognitive impairment in retired professional football players. Neurosurgery. 2005;57(4): 719-726.
McKee AC, Gavett BE, Stern RA, et al. TDP-43 proteinopathy and motor neuron disease in chronic traumatic encephalopathy. J Neuropathol Exp Neurol. 2010;69(9):918-929.