The role of pupillometry in the diagnosis and prognosis of mild traumatic brain injury:
A pilot study at The United States Military Academy at West Point
21 - The role of pupillometry in the diagnosis and prognosis of mild traumatic brain injury:A pilot study at The United States Military Academy at West Point
Neurosurgery resident Walter Reed National Military Medical Center
Abstract Text: The diagnosis of mild traumatic brain injury (mTBI, concussion) relies mainly on subjective symptom reporting through the use of various tools such as the Sport Concussion Assessment Tool 5th Edition (SCAT5) and therefore can have substantial bias. Additionally, current diagnostic techniques provide no information as when athletes can return to play after injury. Typically, after concussion, the neurological exam is without motor or sensory deficit, the brain imaging study is normal, and the clinical evaluation is restricted to subjective reporting of symptoms. Evidence suggests that subjects with mTBI may have some degree of transitory post-injury autonomic dysfunction, therefore, the evaluation of the autonomic system-mediated pupillary light reflex could provide measurements reflecting the activity of the autonomic nervous system after concussion. The goal of our study was to perform baseline and post-injury pupillometric evaluation of cadets at The United States Military Academy at West Point and correlate these measurements with clinical assessment tools--such as SCAT5, the Balance Error Scoring System (BESS) and the Standardized Assessment of Concussion (SAC). The pupillary reaction was measured using an automated handheld device Neuroptics PLR 3000. Nine pupillary light reflex parameters were collected: (1) MAX – maximum pupillary diameter (mm), (2) MIN – minimal pupillary diameter (mm), (3) CON% - percentage of constriction, (4) Latency (seconds to onset of constriction after the light stimulus), (5) ACV – average constriction velocity (mm/s), (6) MCV – maximum constriction velocity (mm/s), (7) ADV – average dilation velocity (mm/s), (8) T75 – seconds from MIN to 75% of MAX, (9) End-In – difference between end and initial pupil size (mm). Separate linear mixed effect models were used to examine change for each of the different pupillary measures with respect to time. Specifically, these models evaluated the change in these pupillary measures for different timepoints at follow-up (see below) relative to baseline timepoint, assuming two-sided tests and significance level=0.05. Pupillary measures were also examined with respect to return to restricted activity. Given the activity measure was not normally distributed, it was dichotomized based on its median value as < 20 days, > 20 days. Mann-Whitney tests were used to compare the pupillary measures for the different timepoints across the dichotomized groups at a significance level=0.05. Six hundred cadets completed baseline (T0) pupillometry and clinical assessments. From these, 39 cadets had mTBI and they were followed with repeated within 48 h post-injury (T1), at the time of becoming asymptomatic (T2), and at the time of return to unrestricted activity (T3). There was no difference in pupillometry parameters between the injured and non-injured cohorts at baseline (T0). Importantly, MCV, MAX, ADV, CON%, and End-In showed significant time-dependent changes with the maximal alteration 48 h after injury (T1) and progressive normalization at T2 and T3. These pupillary changes paralleled those observed in SCAT5 and BESS. When dichotomizing the injured cohort based on early ( < 20 days) or late (>20 days) return to unrestricted activity, some pupillary parameters as measured at T1 were predictive of earlier return (MCV, p=0.03, and End-In p=0.02). In conclusion, this pilot study shows that pupillometry may be an objective diagnostic tool in the acute phase after mTBI and selected pupillary measurements could be predictive of the time for returning to unrestricted activity.