The Association Between Traumatic Brain Injury and the Risk of Cognitive Decline: An Umbrella Systematic Review and Meta-Analysis.

Background: There is currently increasing interest in the implication of traumatic brain injury (TBI) as a potential risk factor for long-term neurodegenerative conditions, such as dementia and Alzheimer's disease (AD). In this context, we performed a systematic review and meta-analysis to evaluate the association between TBI and the risk of dementia.

Methods: A systematic search was performed across multiple electronic databases, including PubMed, Embase, and Cochrane Library, to identify relevant meta-analyses and cohort studies. Studies were included if they reported effect sizes (odds ratios [ORs] or relative risks [RRs]) for the association between TBI, its severity, and the risk of dementia or AD. Meta-analyses were performed using random-effects models to account for heterogeneity, and sensitivity analyses were conducted.

Results: A total of six studies were included in the analysis. The pooled results showed that TBI significantly increases the risk of dementia, with an overall odds ratio of 1.81 (95% CI: 1.53-2.14). Mild TBI was associated with a modest increase in dementia risk (OR = 1.96, 95% CI: 1.70-2.26), while moderate-to-severe TBI showed a stronger association (OR = 1.95, 95% CI: 1.55-2.45). In contrast, the association between TBI and AD was less consistent, with the pooled OR for AD being 1.18 (at 95% CI: 1.11-1.25) for mild TBI; however, in several studies, no significant association was observed (OR = 1.02, 95% CI: 0.91-1.15). The results also indicated substantial heterogeneity across studies, particularly in relation to AD outcomes.

Conclusions: The findings from this umbrella meta-analysis confirm that TBI is a significant risk factor for dementia, with more severe TBIs conferring a higher risk. While mild TBIs also increase the risk of dementia, the effect is more pronounced in moderate-to-severe injuries. The evidence linking TBI to AD is less robust, with inconsistent findings across studies. Clinicians should consider long-term cognitive screening and management for individuals with a history of TBI, particularly those with moderate-to-severe injuries.