Neurologic Diagnoses Before and After Traumatic Brain Injury

BACKGROUND AND OBJECTIVES: Traumatic brain injury (TBI) during mid-to-late life is associated with increased risk of stroke, Parkinson disease (PD), epilepsy, and dementia. These conditions may also predispose to TBI. Thus, we investigated the incidence of dementia, stroke, epilepsy, and PD in older Veterans before and after acute TBI to determine whether there is a bidirectional association. METHODS: In this retrospective cohort study, we identified Veterans aged ≥55 years who received care at US Veterans Health Affairs (VHA) facilities between October 1, 1999, and September 30, 2021, and who had acute TBI (concurrent International Classification of Diseases (ICD) code + emergency department visit + brain imaging) using VHA databases. We matched participants 3:1 to a non-TBI cohort based on age, sex, race/ethnicity, and visit date. Incident stroke, PD, epilepsy, and dementia were determined from ICD codes one year before and after TBI in the TBI cohort and over a two-year period in the non-TBI cohort. We excluded those with prevalent conditions at least 1 year before the study period. Incidence rate ratios (IRRs) and 95% CIs were calculated by comparing the pre-TBI period with the post-TBI period and with the non-TBI cohort. RESULTS: We included 13,801 Veterans with acute TBI and a balanced cohort of 41,403 Veterans without TBI (average age 77.8 years, 96.5% male). Veterans with TBI had higher incidence rates of the 4 conditions before TBI compared with the non-TBI cohort: incidence of stroke (IRR = 3.2 [95% CI 2.9-3.5]), dementia (IRR = 3.1, [95% CI 2.9-3.4]), and PD (IRR = 3.0 [95% CI 2.4-3.7]) was 3 times higher, and that of epilepsy was over 4 times higher (IRR = 4.4 [95% CI 3.6-5.4]). Results were slightly attenuated but remained significant after adjusting for comorbidities and health care utilization. Veterans with TBI also had higher incidence rates 1 year after TBI compared with the pre-TBI period. Incident stroke (IRR = 1.83 [95% CI 1.65-2.04]) and epilepsy (IRR = 2.29 [95% CI 1.88-2.78]) rates were twofold higher; dementia incidence was also higher (IRR = 1.24 [95% CI 1.12-1.38]), but PD rates did not differ (IRR = 1.06 [95% CI 0.82-1.36]). DISCUSSION: We found a bidirectional association between TBI and several neurologic conditions, with higher incidence rates preceding TBI and higher rates after TBI. Generalizability to non-Veteran populations is uncertain. Future studies may determine whether TBI prevention measures for adults with stroke, dementia, PD, and epilepsy are warranted.