Risk Factors for Mild Traumatic Brain Injury and Subsequent Post-Traumatic Stress Disorder and Mental Health Disorders among United States Army Soldiers

The purpose of this study was to determine the association of mild traumatic brain injury (mTBI) with subsequent post-traumatic stress disorder (PTSD) and mental health disorders (MHD), and the intervening role of acute stress disorder (ASD). This matched case-control study utilized the Total Army Injury and Health Outcomes Database (TAIHOD) to analyze soldiers' (n = 1,261,297) medical encounter data between 2002 and 2011. International Classification of Diseases, Ninth Revision (ICD-9) codes were used to identify: mTBI (following Centers for Disease Control [CDC] surveillance definition for mTBI), MHD (ICD-9 codes for depression and anxiety, excluding PTSD), PTSD (ICD-9 309.81), and ASD (ICD-9 308.3). Incident cases of mTBI (n = 79,505), PTSD (n = 71,454), and MHD (n = 285,731) were identified. Overall incidence rates per 1000 soldier years were: mTBI = 17.23, PTSD = 15.37, and MHD = 67.99. mTBI was associated with increased risk for PTSD (risk ratio [RR] 5.09, 95% confidence interval [CI] 4.82-5.37) and MHD (RR 2.94, 95% CI 2.84-3.04). A sub-analysis of the mTBI-only soldiers found that a diagnosis ASD, compared with a diagnosis of no ASD, was associated with greater risk for subsequent PTSD (RR 2.13, 95% CI 1.96-2.32) and MHD (RR 1.90, 95% CI 1.72-2.09) following mTBI. Results indicate that soldiers with previous mTBI have a higher risk for PTSD and MHD, and that ASD may also mediate PTSD and MHD risk subsequent to mTBI. These data may help guide important surveillance and clinical rehabilitation considerations for high-risk populations.