The Relationship Between Traumatic Brain Injury and the Neuropathology of Dementia

Background Clinical studies indicate that traumatic brain injury (TBI) is linked to an increased risk of dementia during life. However, studies involving neuropathologically‐confirmed cases have shown conflicting results. This study was aimed at assessing a large brain bank cohort to identify any association between TBI and the presence of pathologies underlying the most commonly found dementias, Alzheimer’s disease (AD) and Lewy body disease (LBD). Method 636 cases were assessed for this study (average age 76.2). Cases with a history of TBI were identified using donor records held at the Sydney Brain Bank. We use the term "TBI” to include a single or multiple TBIs, as well as repetitive mild neurotrauma that may be subconcussive (N = 109). Amyloid plaque and alpha synuclein pathologies were identified by immunohistochemistry. Neurofibrillary tangles were identified using modified Bielschowsky silver staining. Pathology was assessed according to current neuropathological diagnostic criteria. Multivariate regression statistics were used to assess the effect of TBI, age and gender on amyloid plaque (A score), neurofibrillary tangles (B score) and Lewy pathology stages. Multinomial logistic regression was used to examine the effect of TBI on pathological diagnosis. Results TBI was not significantly associated with increased amyloid (p = 0.05) or Lewy pathology stages (p = 0.65), however the odds of having a higher neurofibrillary tangle stage increased by 75% in the TBI group (p = 0.009)(Figure 1). Gender was not a significant predictor of amyloid (p = 0.29), neurofibrillary tangle (p = 0.89) or Lewy pathology (p = 0.15). Not unexpectedly, age was a significant predictor of AD pathologies, including amyloid (p = <0.0000001) and neurofibrillary tangle (p = 0.00002) stages, although age was not a significant driver of Lewy body pathology (p = 0.1). There was no association between TBI and overall diagnosis of AD neuropathologic change or LBD (p = 0.12). Conclusions In this elderly neurodegenerative cohort, age remains a risk factor for AD, but not LBD pathology. Gender did not have a significant association with these pathologies in this cohort. TBI did not increase the risk of AD but did increase the frequency of neurofibrillary tangles, suggesting that abnormal tau protein accumulation following TBI is an important long‐term consequence that may contribute to poor brain aging and future neurodegeneration.