Widespread Tau and Amyloid‐Beta Pathology Many Years After a Single Traumatic Brain Injury in Humans

While a history of a single traumatic brain injury (TBI) is associated with the later development of syndromes of cognitive impairment such as Alzheimer's disease, the long-term pathology evolving after single TBI is poorly understood. However, a progressive tauopathy, chronic traumatic encephalopathy, is described in selected cohorts with a history of repetitive concussive/mild head injury. Here, post-mortem brains from long-term survivors of just a single TBI (1-47 years survival; n=39) vs. uninjured, age-matched controls (n=47) were examined for neurofibrillary tangles (NFTs) and amyloid-β (Aβ) plaques using immunohistochemistry and thioflavine-S staining. Detailed maps of findings permitted classification of pathology using semiquantitative scoring systems. NFTs were exceptionally rare in young, uninjured controls, yet were abundant and widely distributed in approximately one-third of TBI cases. In addition, Aβ-plaques were found in a greater density following TBI vs. controls. Moreover, thioflavine-S staining revealed that while all plaque-positive control cases displayed predominantly diffuse plaques, 64% of plaque-positive TBI cases displayed predominantly thioflavine-S-positive plaques or a mixed thioflavine-S-positive/diffuse pattern. These data demonstrate that widespread NFT and Aβ plaque pathologies are present in up to a third of patients following survival of a year or more from a single TBI. This suggests that a single TBI induces long-term neuropathological changes akin to those found in neurodegenerative disease.