A Retrospective Study of Predictors of Return to Duty versus Medical Retirement in an Active Duty Military Population with Blast-Related Mild Traumatic Brain Injury

Abstract

Traumatic Brain Injury (TBI) has been described as the "signature injury" of the Global War on Terror. Explosive blast TBI has become a leading cause of injury as a result of the widespread use of improvised explosive devices in Iraq and Afghanistan. We present a retrospective cross-sectional study of patients with blast-related mild TBI (mTBI, N = 303) seen at the Intrepid Spirit Concussion Recovery Center at Naval Medical Center Camp Lejeune. The objective was to predict outcomes of return to duty (RTD) vs. medical retirement via medical evaluation board (MEB), based on brain imaging, neuropsychological data, and history of mTBI. The motivation is to inform prognosis and target resources to improve outcomes for service members who are less likely to RTD through the standard treatment program. The RTD was defined operationally as individuals who completed treatment and were not recommended for medical retirement or separation for TBI or related sequelae. Higher scores on the Repeatable Battery for Neuropsychological Status (RBANS) test were associated positively with RTD (p = 0.001). A history of three or more lifetime concussions was associated negatively with RTD, when compared with one concussion (p = 0.04). Elevated apparent diffusion coefficient (ADC) in the anterior corona radiata was associated negatively with RTD (p = 0.04). A logistic regression model was used to classify individuals with RBANS and imaging data (n = 81) as RTD or MEB according to RBANS, ADC, and a history of multiple (≥3) concussions. The RBANS (p = 0.003) and multiple concussions (p = 0.03) were significant terms in the logistic model, but ADC was not (p = 0.27). The area under the receiver operating characteristic curve was 0.77 (95% confidence interval 0.66-0.86). These results suggest cognitive testing and TBI history might be used to identify service members who are more likely to be retired medically from active duty.

Keywords: RBANS; blast; mTBI; return to duty; white matter.

Conflict of interest statement

No competing financial interests exist.

Figures

FIG. 1.

The registration pipeline for apparent diffusion coefficient (ADC) analysis. (a) The population template is built from 100 randomly selected fluid attenuation inversion recovery (FLAIR) images. (b) The registration pipeline computes a series of transforms that are combined to warp ADC and white matter regions of interest to the subject space.

FIG. 2.

Region of interest (ROI) post-processing. The labels are first warped to the subject image from the template. The warped labels are refined by removing voxels where the apparent diffusion coefficient (ADC) is above a maximum threshold, or where the segmentation of the fluid attenuation inversion recovery (FLAIR) image classifies the voxel as cerebrospinal fluid.

FIG. 3.

Repeatable Battery for Neuropsychological Status (RBANS) overall performance and domain scores. RBANS total scores were significantly lower for the medical evaluation board (MEB) group. Within individual domains, attention and immediate memory were significantly lower in the MEB group. Boxes show interquartile range (IQR) with a black line indicating the median. Whiskers extend to 1.5 * IQR; points outside this range are shown as black circles.

FIG. 4.

Apparent diffusion coefficient (ADC) in the anterior corona radiata (ACR) for scans at different spatial resolutions. Subjects with undetermined medical evaluation board (MEB) status were not included in the regression analyses, but are plotted here as further data points showing that imaging resolution is correlated with the measured ADC. Boxes show interquartile range (IQR) with a black line indicating the median. Whiskers extend to 1.5 * IQR; points outside this range are shown as black circles.

FIG. 5.

Logistic regression output used as a classifier. The curve shows the specificity and sensitivity of different classification thresholds. The highlighted point has the maximum sum of sensitivity and specificity along the curve. ROC, receiver operating characteristic.