A quick, noninvasive, handheld device that detects changes in pupil size may offer rapid assessment of potential brain injury in young athletes who have sustained a high-impact hit to the head but who exhibit no obvious signs of brain injury.
A small longitudinal study showed that quantitative pupillometry (QP) was able to detect “measurable” neurologic effects of high-acceleration head impacts (HHIs) in high school football players who had no clinical signs or symptoms and who had not been diagnosed with concussion.
“These findings suggest that these severe head impacts, which account for one in a thousand of all head impacts, may cause subtle changes in the brain that have been previous unrecognized,” lead author Jacob R. Joseph, MD, clinical instructor and fellow in neurotrauma, University of Pittsburgh, Pennsylvania, told Medscape Medical News.
“During games, any time an athlete suffers an obvious severe head impact, that athlete should be evaluated for head injury carefully, even if there are no overt signs and symptoms,” he said.
The study was published online November 26 in the Journal of Neurosurgery.
Previous research suggests that clinically asymptomatic HHIs are associated with neuronal and axonal injury, which is only detectable with advanced imaging and biomarkers.
However, investigators note that these methods are time-consuming, invasive, and costly, and they highlight the need for a quick, noninvasive measurement tool.
QP, they note, is “a potential objective, rapid, noninvasive measurement tool that may be used to assess the neurological effects of HHIs.”
A “rapid, objective, noninvasive method to identify athletes at risk and diagnose concussion would be a major advance,” they write.
The investigators point out that QP has become “commonplace, especially in the neurointensive care setting.” It has the advantage of “being an objective and quantifiable biometric test” — unlike the use of a penlight to evaluate the pupillary light reflect, which may “involve subjective interpretation, particularly in cases in which there are subtle findings.”
QP measures eight parameters of pupil size and reactivity and takes only 2 minutes per session to administer.
In a previous study, Joseph and colleagues found changes in blood biomarkers after HHI, “and we wanted to evaluate this by seeing if there was a physiologic change in these athletes,” he said.
“We designed this study to identify if there were subtle signs of brain injury [in asymptomatic athletes with severe HHI] that we might have been missing. We hypothesized that severe head impacts are the mostly likely to be causing unrecognized injury,” Joseph added.
The researchers followed 18 high school football players through a single season. They monitored the frequency and magnitude of any head impact the athletes sustained and conducted pupillary assessments at baseline, midseason, after occurrence of the HHI (when relevant), and at the end of the season.
Prior to the start of the study, eight athletes had sustained ≥1 concussions, and five had sustained two previous concussions.
Each athlete wore a helmet fitted with an encoder for the Head Impact Telemetry System, which measured and recorded head impact data during all practices and games.
All of the athletes underwent a preseason neurocognitive evaluation with the Sport Concussion Assessment Tool, 5th Edition. QP was performed during a period of rest, rather than after an athletic event.
Altered Brain Pathways
Participants were monitored for concussion symptoms. Those who were diagnosed with sports-related concussion received repeated neurocognitive evaluation and QP immediately after the event in which the athlete suffered an HHI (defined as “an impact that simultaneously achieved a linear acceleration of > 95g and a rotational acceleration of > 3760 rad/sec2).
During the study, there were 37 practices, 12 games, and 7045 hits to the head.
Of the original 18 participants, five were excluded, one withdrew from the study, two sustained orthopedic injuries, and two did not complete the process, leaving 13 study participants.
During the course of the season, seven athletes experienced an HHI. For six of these individuals, the injury occurred prior to the midpoint evaluation.
When the researchers used the midpoint evaluation as a within-subject control, they found significant decreases in dilation velocity, as measured by the QP (mean difference, 0.139 mm/sec; P = .048).
At the assessments made after the HHI, the researchers also found a change in pupil diameter (mean difference, 3.643%; P = .002), as well as maximum constriction velocity (mean difference, .744% mm/sec; P = .010), when compared to values at the athletes’ own midpoint evaluations.
The pupillometer revealed no significant difference in the maximum size metric (maximum diameter), minimum size metric (minimum diameter), latency to constriction, or constriction velocity at the same time points (all Ps > .05).
However, there were significant differences in the QP over the course of the season in constriction velocity (P = .019) as well as maximum constriction velocity (P = .043).
There were no significant changes in neurocognitive test results over the course of the season.
The authors conclude that the “forces experienced by these athletes were sufficient to alter intrinsic brain pathways.”
The study findings are important because “most of the current research asserts that all head impacts are the same and that all head impacts cause brain damage,” Joseph said.
“Our findings suggest that it may in fact only be the most severe head impacts — one in a thousand — that can cause measurable injury.”
He referred to HHI as an “actionable entity,” suggesting that the number of HHIs can potentially be reduced or even “eliminated from the game with either rule changes or technological advances.”
Quick, Simple Test
Commenting on the study for Medscape Medical News, Paul Brennan, MD, PhD, consultant neurosurgeon, University of Edinburgh, United Kingdom, who was not involved in the research, said it might be “of particular value in assessing athletes who are asymptomatic after head injury.”
A caveat is that the authors’ conclusion and its significance “need substantiating in a much larger cohort of patients,” he noted.
“In the absence of correlation of the pupillary changes with neurocognitive changes, it needs to be established what, if any, relationship there is between pupillary changes and clinical signs and symptoms — the cornerstone of concussion,” said Brennan.
Nevertheless, “the quick, simple test described here may provide an opportunity to objectively assess the severity of concussion-type injuries and provide the much sought after opportunity to establish whether these events correlate to longer-term outcome.”
Joseph added that team physicians, trainers, and parents should try to limit severe hits to the head as much as possible — “meaning that during controlled sessions such as practices, situations that could lead to HHIs should really be eliminated…and all athletes at all levels should have a well-fitting helmet.”
Joseph reports having received support for the study from NeurOptics, Inc, and the Blue Cross Blue Shield Foundation of Michigan. The other authors’ disclosures are listed in the original article. Brennan reports no relevant financial relationships.
J Neurosurg. Published online November 26, 2019. Abstract