The role of deployment history on the association between epilepsy and traumatic brain injury in post-9/11 era U.S. Veterans

Abstract: BACKGROUND AND OBJECTIVES: Traumatic brain injury (TBI) is a well-established epilepsy risk factor and is common among service members. Deployment related TBI, where combat/blast may be more common, may have different outcomes than non-deployment related TBI. This work examined associations of all TBI exposures (not just combat), and epilepsy, while adjusting for comorbidities associated with epilepsy, among Veterans by deployment status. METHODS: The cohort included post-9/11 Veterans with ≥ 2 years of care in both Veterans Health Administration (VHA) and Defense Health Agency (DHA) systems. We identified epilepsy using ICD-9/10-CM codes, anti-seizure medication, and service-connected disability for epilepsy. We conducted a logistic regression model with interaction terms for conditions by deployment history that adjusted for demographics and military characteristics. RESULTS: The cohort (n=938,890) included post-9/11 Veterans of which 27,436 (2.92%) had epilepsy. Most Veterans had a history of deployment (70.64%), referred to as "deployed". Epilepsy was more common among Veterans who were never deployed ("non-deployed") (3.85% vs. 2.54%). Deployed Veterans were more likely to have had TBI, compared to the non-deployed (33.94% vs. 4.24%), but non-deployed Veterans with moderate/severe TBI had higher odds of epilepsy compared to deployed Veterans (aOR=2.92, 95% CI: 2.68-3.17 vs. aOR=2.01, 95% CI: 1.91-2.11). Penetrating TBI had higher odds of epilepsy among the deployed (aOR=5.33, 95% CI: 4.89-5.81), whereas the odds of epilepsy for mild TBI did not significantly differ by deployment status. Though most neurological conditions were more prevalent among non-deployed, they were often associated with higher odds of epilepsy in the deployed. DISCUSSION: Deployment history had a significant differential impact on epilepsy predictors. As expected, penetrating TBI had a greater epilepsy impact among deployed Veterans perhaps due to combat/blast. Some epilepsy predictors (moderate/severe TBI, MS, Parkinson's disease) had a stronger association in the non-deployed suggesting a potential healthy warrior effect in which such conditions preclude deployment. Other neurological conditions (e.g., brain tumor, Alzheimer's disease/frontotemporal dementia) had a greater epilepsy impact in the deployed. This may be attributable to deployment related exposures (combat injury, occupational exposures). A better understanding of deployment effects is critical to provide targeted epilepsy prevention in Veterans and military service members.

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