Data from the National Alzheimer Coordinating Center suggest that TBI may be a risk factor for early-onset (<65 years) Alzheimer disease and that disinhibition is more likely to occur in those with both Alzheimer disease and a history of TBI.6 Moreover, findings from a recent meta-analysis suggest an association between TBI and Parkinsonian signs or risk for incident Parkinson disease.7
This literature suggests that in a subset of individuals with a predisposition to develop a neurodegenerative disorder, TBI influences the timing and nature of onset and progression. Although not discussed here due to inconsistencies in the literature, a separate neurodegenerative process directly related to repetitive TBI—chronic traumatic encephalopathy—is also likely to exist.
New onset TBI in the aged
At every point along the arc of a newly sustained TBI, from pre-injury risk factors to acute symptoms and future complications, there exists a nuanced set of geriatric-specific factors to consider. Falls, largely from standing height, are the leading mechanism of TBI in older adults with more women affected.8 As even a single fall is a risk factor for subsequent falls, older adults may be at risk for repetitive TBI.
TBIs that would otherwise be classified as mild place older adults at risk for intracranial bleeding due to intra-cranial changes that occur with aging (eg, dura adherence to the skull, bridging vein fragility, cerebrovascular atherosclerosis) and the increased use of anticoagulant medication. Following a blunt head trauma, older adults may produce a completely normal neurological examination, yet still have evidence of intracranial trauma on head computerized tomography.9 Older adults are also more likely to have pre-existing medical conditions that are associated with worse post-TBI outcomes.10
The cumulative effect of these factors is that, on average, older adults with TBI experience higher morbidity and mortality, slower recovery trajectories, and worse functional, cognitive, and psychosocial outcomes than younger individuals. Layering the variable of aging onto the already complex TBI equation makes outcome prediction all the more difficult.11
Global outcome measures indicate that older adults have greater functional dependence after TBI.8 Unfortunately, differences in cognitive and other neuropsychiatric symptoms between younger and older adults with new onset TBI are vastly understudied. There appears to be an increased dementia risk when new onset TBI is experienced at an older age compared with younger age, particularly for mild TBI (moderate-to-severe TBI more consistently associated at any age).12
Evidence indicates that when it comes to preexisting psychiatric diagnoses, older adults experiencing TBI are less likely to have a previously diagnosed psychiatric disorder.13 TBI significantly increases the risk of new onset depression, anxiety, and/or PTSD in older adults, with evidence of under-recognition and under-treatment.14 On a more positive note, there appears to be a subset of older adults with TBI who achieve outcomes similar to younger patients, which indicates that chronological age and TBI severity are not the sole determinants of outcome.15
Dr Narapareddy is a Neuropsychiatry Fellow, Ms Richey is Research Coordinator, and Dr Peters is Assistant Professor, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD.
The authors report no conflicts of interest concerning the subject matter of this article.
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