A handheld device that detects changes in pupil size may offer rapid assessment of potential 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 previously unrecognized," says lead author Jacob R. Joseph, MD, of the University of Pittsburgh.
Previous research has suggested that clinically asymptomatic HHIs are associated with neuronal and axonal injury, which is only detectable with advanced imaging and biomarkers.
The investigators note that QP 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."
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. Of the original 18 participants, 13 completed the process.
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. QP was performed during a period of rest, rather than after an athletic event.
Prior to the study, eight athletes had sustained one or more concussions; five had sustained two previous concussions. During the study, there were 37 practices, 12 games, and 7,045 hits to the head.
Participants who were diagnosed with sports-related concussion received repeated neurocognitive evaluation and QP immediately after the event in which the athlete suffered an HHI.
During the course of the season, seven athletes experienced an HHI. For six, 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.
At the assessments made after the HHI, the researchers also found a change in pupil diameter, as well as maximum constriction velocity, when compared to values at the athletes' own midpoint evaluations.
The pupillometer revealed no significant difference in the maximum size metric, minimum size metric, latency to constriction, or constriction velocity at the same time points. However, there were significant differences in the QP over the course of the season in constriction velocity as well as maximum constriction velocity.
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 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."
Source: Medscape, December 2, 2019