Among 502,154 UK Biobank participants, individuals carrying both a lifetime traumatic brain injury (TBI) history and a subsequent neurological diagnosis — dementia, stroke, or Parkinson's disease — faced the highest psychiatric burden of any group, exceeding risks seen with either condition alone. Mood disorders emerged as the most consistent psychiatric outcome across all three neurological cohorts, while anxiety associations were less reliable. Ten-year Kaplan-Meier and Cox proportional hazards analyses confirmed elevated cumulative incidence of mood and broader mental health disorders in every TBI-plus-neurological-disease subgroup.
This preprint, not yet peer-reviewed, adds epidemiological weight to a mechanistically plausible but underappreciated interaction: TBI accelerates neuroinflammatory cascades, disrupts monoaminergic circuits, and compromises white-matter integrity — vulnerabilities that neurological diseases like dementia and Parkinson's further exploit. The practical implication is significant for aging populations, where falls-related TBI and progressive neurological disease frequently overlap. Clinicians routinely screen for depression in Parkinson's and post-stroke, yet TBI history is rarely incorporated into that psychiatric risk calculus. The study's observational design means causality cannot be confirmed, and UK Biobank's healthier-than-average volunteer base may underestimate real-world prevalence. Biobank TBI ascertainment also relies partly on self-report and hospital records, potentially missing mild injuries. Still, the cohort size lends statistical credibility. If confirmed through peer review, this finding argues for routine TBI history-taking as a standard component of neuropsychiatric assessment in older adults with neurological diagnoses.
