What Is the Relationship of Traumatic Brain Injury to Dementia?

J Alzheimers Dis. 2017;57(3):667-681. doi: 10.3233/JAD-161002.

Abstract

There is a long history linking traumatic brain injury (TBI) with the development of dementia. Despite significant reservations, such as recall bias or concluding causality for TBI, a summary of recent research points to several conclusions on the TBI-dementia relationship. 1) Increasing severity of a single moderate-to-severe TBI increases the risk of subsequent Alzheimer's disease (AD), the most common type of dementia. 2) Repetitive, often subconcussive, mild TBIs increases the risk for chronic traumatic encephalopathy (CTE), a degenerative neuropathology. 3) TBI may be a risk factor for other neurodegenerative disorders that can be associated with dementia. 4) TBI appears to lower the age of onset of TBI-related neurocognitive syndromes, potentially adding "TBI cognitive-behavioral features". The literature further indicates several specific risk factors for TBI-associated dementia: 5) any blast or blunt physical force to the head as long as there is violent head displacement; 6) decreased cognitive and/or neuronal reserve and the related variable of older age at TBI; and 7) the presence of apolipoprotein E ɛ4 alleles, a genetic risk factor for AD. Finally, there are neuropathological features relating TBI with neurocognitive syndromes: 8) acute TBI results in amyloid pathology and other neurodegenerative proteinopathies; 9) CTE shares features with neurodegenerative dementias; and 10) TBI results in white matter tract and neural network disruptions. Although further research is needed, these ten findings suggest that dose-dependent effects of violent head displacement in vulnerable brains predispose to dementia; among several potential mechanisms is the propagation of abnormal proteins along damaged white matter networks.

Keywords: Alzheimer’s disease chronic traumatic encephalopathy; dementia; traumatic brain injury.

Publication types

  • Review
  • Research Support, N.I.H., Extramural

MeSH terms

  • Apolipoprotein E4 / genetics
  • Brain / diagnostic imaging
  • Brain / pathology*
  • Brain Injuries, Traumatic* / complications
  • Brain Injuries, Traumatic* / epidemiology
  • Brain Injuries, Traumatic* / pathology
  • Databases, Bibliographic / statistics & numerical data
  • Dementia* / epidemiology
  • Dementia* / etiology
  • Dementia* / pathology
  • Disease Progression
  • Humans
  • Neurodegenerative Diseases* / epidemiology
  • Neurodegenerative Diseases* / etiology
  • Neurodegenerative Diseases* / pathology
  • Risk Factors

Substances

  • Apolipoprotein E4