Epidemiologic aspects of traumatic brain injury in acute combat casualties at a major military medical center: A cohort study

Objective: From the ongoing military conflicts in Iraq and Afghanistan, an understanding of the neuroepidemiology of traumatic brain injury (TBI) has emerged as requisite for further advancements in neurocombat casualty care. This study reports population-specific incidence data and investigates TBI identification and grading criteria with emphasis on the role of loss of consciousness (LOC) in the diagnostic rubric. Methods: This is a cohort study of all consecutive troops acutely injured during combat operations - sustaining body-wide injuries sufficient to require immediate stateside evacuation - and admitted sequentially to our medical center during a 2-year period. A prospective exploration of the TBI identification and grading system was performed in a homogeneous population of blast-injured polytrauma inpatients. Results: TBI incidence was 54.3%. Structural neuroimaging abnormalities were identified in 14.0%. Higher Injury Severity Score (ISS) was associated with abnormal neuroimaging, longer length of stay (LOS), and elevated TBI status - primarily based on autobiographical LOC. Mild TBI patients had normal neuroimaging, higher ISS, and comparable LOS to TBI-negative patients. Patients who reported LOC had a lower incidence of abnormal neuroimaging. Interpretation: This study demonstrates that the methodology used to assign the diagnosis of a mild TBI in troops with complex combat-related injuries is crucial to an accurate accounting. The detection of incipient mild TBI, based on an identification system that utilizes LOC as the principal diagnostic criterion to discern among patients with outcomes of interest, misclassifies patients whose LOC may not reflect actual brain injury. Attempts to identify high-risk battlefield casualties within the current point-of-injury mild TBI case definition, which favors high sensitivity, will be at the expense of specificity.