Traumatic brain injury and risk of dementia in older veterans

Abstract

Objectives: Traumatic brain injury (TBI) is common in military personnel, and there is growing concern about the long-term effects of TBI on the brain; however, few studies have examined the association between TBI and risk of dementia in veterans.

Methods: We performed a retrospective cohort study of 188,764 US veterans aged 55 years or older who had at least one inpatient or outpatient visit during both the baseline (2000-2003) and follow-up (2003-2012) periods and did not have a dementia diagnosis at baseline. TBI and dementia diagnoses were determined using ICD-9 codes in electronic medical records. Fine-Gray proportional hazards models were used to determine whether TBI was associated with greater risk of incident dementia, accounting for the competing risk of death and adjusting for demographics, medical comorbidities, and psychiatric disorders.

Results: Veterans were a mean age of 68 years at baseline. During the 9-year follow-up period, 16% of those with TBI developed dementia compared with 10% of those without TBI (adjusted hazard ratio, 1.57; 95% confidence interval: 1.35-1.83). There was evidence of an additive association between TBI and other conditions on risk of dementia.

Conclusions: TBI in older veterans was associated with a 60% increase in the risk of developing dementia over 9 years after accounting for competing risks and potential confounders. Our results suggest that TBI in older veterans may predispose toward development of symptomatic dementia and raise concern about the potential long-term consequences of TBI in younger veterans and civilians.

Figure 1. Age at dementia diagnosis in veterans with and without TBI, accounting for mortality

The cumulative incidence of dementia is shown for veterans with traumatic brain injury (TBI) at baseline (orange) and without TBI at baseline (green), accounting for the competing risk of mortality. Age is used as the time scale to indicate age at dementia diagnosis.

Figure 2. Additive effects of TBI and other risk factors on dementia incidence

The additive association between traumatic brain injury (TBI) and other dementia risk factors is illustrated by showing the cumulative incidence of dementia with age as the time scale for veterans with TBI only (blue), other risk factor only (orange), both risk factors (brown), or neither risk factor (green). Other risk factors examined include depression (A), posttraumatic stress disorder (PTSD) (B), and cerebrovascular disease (CVD) (C).