Yasmin Aziz, MD

Brett BL, Kerr ZY, Aggarwal NT, Chandran A, Mannix R, Walton S, DeFreese JD, Echemendia RJ, Guskiewicz KM, McCrea MA, Meehan III WP. Cumulative Concussion and Odds of Stroke in Former National Football League Players. Stroke. 2021.

In the last 20 years, the discovery of chronic traumatic encephalopathy has captured the attention of both the scientific and athletic communities, sparking a renewed interest in sports safety and concussion protocols. Inspired by preclinical studies, the authors for this article sought to examine if another feared neurologic complication, stroke, is associated with lifetime concussion exposure. In this cross-sectional study, nearly 979 men 50 years or older with at least one year’s experience in the National Football League (NFL) were sent a questionnaire asking about demographics, current functioning, as well as medical, football, concussion, and stroke history. Concussion was specifically defined using standard definition (i.e., not restricted to only episodes of being “knocked out”), and stroke history was defined by a personal history of obtaining this diagnosis from a healthcare provider. Concussion number was subgrouped into 5 categories: 0, 1-2, 3-5, 6-9, and 10 or more events. Traditional demographic risk factors were collected and placed in a multivariate logistic model to estimate adjusted odds ratio (aOR) for stroke.

Surprisingly, the prevalence of stroke in their cohort was only 3.4% (n=33), significantly less than the expected event rate in an age-matched population. Of the traditional covariates studied, only history of coronary disease and age were significant. When these factors were adjusted for in the multivariate analysis, men with 10 or more concussions had 5 times higher odds of sustaining a stroke than men without [aOR (95% CI) = 5.51 (1.61-28.95), see Figure below]. The authors, therefore, concluded that repeated traumatic brain injury is likely an independent risk factor for stroke.

Figure. Predicted probability of stroke history.
Figure. Predicted probability of stroke history.

While the authors reference white matter disease on neuroimaging of NFL players, the specific pathology connecting TBI and stroke remains elusive. The study, though bolstered by a large sample size, is limited by its cross-sectional design and self-reported patient outcomes. Prospectively collected cohort data linked to electronic medical record information including all concussions, neuroimaging findings, and stroke will be needed to determine whether concussion is truly an independent risk factor for stroke. Until then, this study serves as another possible harbinger of the dangerous repercussions of recurrent head injury.