High-impact blows to the head raised biomarkers of traumatic brain injury (TBI) in non-concussed high school varsity football players, according to a small prospective observational study of 16 athletes published in the Journal of Neurosurgery on July 3.
Football players are vulnerable to repetitive blows to the head or body that may not produce the clinical signs and symptoms of a concussion or may not be detectable during a routine neurologic examination. Moreover, some athletes may not notice subtle symptoms, such as changes in behavior, attention, or emotional response, or they may not report symptoms to avoid clinical testing and continue to play.
Due to the difficulty of diagnosing a mild TBI, researchers check for blood biomarkers, which can be quantified objectively. Previous research has revealed axonal proteins, such as tau, and neuronal proteins, such as ubiquitin C-terminal hydrolase L1 (UCH-L1), are elevated after a mild TBI. The presence of these two biomarkers may provide evidence of brain injury, even in athletes who show no signs of a concussion.
To investigate the relationship between high-speed head blows and mild TBI biomarkers, researchers followed 16 high school varsity football players who wore helmet-based accelerometers that recorded head impact data during practices and games during the 2016 football season.
All 16 athletes underwent a series of tests to measure their neurocognitive abilities, and provided blood samples at the beginning of the season. A second blood sample was taken immediately after the game, in which one of the athletes sustained a high-impact hit. In athletes who did not sustain a high-speed hit, blood samples were taken after the final game of the season. Three to five days after the season was over, all athletes completed the initial series of test to measure cognitive ability and had additional bloodwork.
Six athletes sustained one or more high-speed hits during the season and their blood samples showed that total tau and UCH-L1 levels increased an average of 492.6 percent and 738.2 percent, respectively. Athletes who didn’t sustain high-speed blows saw their tau levels and UCH-L1 levels increase 164 and 237.7 percent, respectively.
In a separate post-season analysis of 12 athletes, researchers found those who did not receive a concussion diagnosis experienced a 64.8 percent increase in tau levels and a 62.6 percent increase in UCH-L1 levels compared to pre-season levels. No significant increases were reported in the serum levels of other TBI biomarkers tested.
High-speed hits to the head, which represent 0.001% of all hits, may be on the same spectrum as concussion, said Jacob R. Joseph, MD, a neurosurgery resident at Michigan Medicine at the University of Michigan, lead author of the study, about the results. It is unknown whether elevated TBI biomarkers are clinically significant, according to the researchers.
The findings warrant further investigation in large-scale prospective trials that look at all brain injury biomarkers in athletes who are more likely to sustain high-impact blows to the head.
In the meantime, understanding brain injury biomarkers could potentially lead to developing a novel way to reduce the incidence of high-speed hits in young athletes.