Importance: Epidemiologic evidence regarding the importance of traumatic brain injury (TBI) as a risk factor for dementia is conflicting. Few previous studies have used patients with non-TBI trauma (NTT) as controls to investigate the influence of age and TBI severity.
Objective: To quantify the risk of dementia among adults with recent TBI compared with adults with NTT.
Design, setting, and participants: This retrospective cohort study was performed from January 1, 2005, through December 31, 2011 (follow-up, 5-7 years). All patients 55 years or older diagnosed as having TBI or NTT in 2005 and 2006 and who did not have baseline dementia or die during hospitalization (n = 164,661) were identified in a California statewide administrative health database of emergency department (ED) and inpatient visits.
Exposures: Mild vs moderate to severe TBI diagnosed by Centers for Disease Control and Prevention criteria using International Classification of Diseases, Ninth Revision (ICD-9)codes, and NTT, defined as fractures excluding fractures of the head and neck, diagnosed using ICD-9 codes.
Main outcomes and measures: Incident ED or inpatient diagnosis of dementia (using ICD-9 codes) 1 year or more after initial TBI or NTT. The association between TBI and risk of dementia was estimated using Cox proportional hazards models before and after adjusting for common dementia predictors and potential confounders. We also stratified by TBI severity and age category (55-64, 65-74, 75-84, and ≥85 years).
Results: A total of 51,799 patients with trauma (31.5%) had TBI. Of these, 4361 (8.4%) developed dementia compared with 6610 patients with NTT (5.9%) (P < .001). We found that TBI was associated with increased dementia risk (hazard ratio [HR], 1.46; 95% CI, 1.41-1.52; P < .001). Adjustment for covariates had little effect except adjustment for age category (fully adjusted model HR, 1.26; 95% CI, 1.21-1.32; P < .001). In stratified adjusted analyses, moderate to severe TBI was associated with increased risk of dementia across all ages (age 55-64: HR, 1.72; 95% CI, 1.40-2.10; P < .001; vs age 65-74: HR, 1.46; 95% CI, 1.30-1.64; P < .001), whereas mild TBI may be a more important risk factor with increasing age (age 55-64: HR, 1.11; 95% CI, 0.80-1.53; P = .55; vs age 65-74: HR, 1.25; 95% CI, 1.04-1.51; P = .02; age interaction P < .001).
Conclusions and relevance: Among patients evaluated in the ED or inpatient settings, those with moderate to severe TBI at 55 years or older or mild TBI at 65 years or older had an increased risk of developing dementia. Younger adults may be more resilient to the effects of recent mild TBI than older adults.