Traumatic brain injury with a loss of consciousness may be associated with later development of Parkinson's disease but not Alzheimer's disease or incident dementia, according to a study conducted at the Icahn School of Medicine at Mount Sinai and the University of Washington School of Medicine.
The research, published in JAMA Neurology, contradicts common assumptions about the relationship between traumatic brain injury and Alzheimer's disease as found in other high-profile studies.
There is great interest in the late effects of traumatic brain injury and the widespread public health implications. The Centers for Disease Control and Prevention ( CDC ) estimates that more than 1.3 million Americans visit an emergency department each year because of a traumatic brain injury-related injury.
The research team studied head injury data from 7,130 older adults as part of three prospective cohort studies that performed annual or biennial cognitive and clinical testing. Of this group, 865 people had suffered traumatic brain injury with loss of consciousness at some point before the study began. Of the 865, 142 had been unconscious for more than one hour.
The researchers evaluated associations between traumatic brain injury and late-life clinical outcomes, such as dementia, Alzheimer's disease, mild cognitive impairment, Parkinson's disease and change in parkinsonian signs.
Roughly 23% of the study group had brain autopsies, and in that group researchers searched for any link between traumatic brain injury and neuropathological findings.
Neuropathology is considered the gold standard for diagnosing neurodegenerative disease.
No statistically significant relationship between traumatic brain injury with loss of consciousness and dementia risk was discovered when the group with traumatic brain injury with loss of consciousness was compared with the 1,537 patients who developed dementia during the study.
Results for Alzheimer's disease ( diagnosed in 1,322 study participants ) were similar. However, regression data showed a strong association between traumatic brain injury with loss of consciousness greater than an hour and Parkinson's disease ( 117 cases during the study ).
Neuropathological findings at autopsy ( 1,652 autopsy cases ) showed no association between traumatic brain injury with loss of consciousness and beta amyloid plaques or neurofibrillary tangles, the hallmark indicators of Alzheimer's disease.
However, the autopsies found an increased risk for Lewy bodies ( abnormal aggregates of protein ) in traumatic brain injury with loss of consciousness less than an hour and an increased risk of cerebral microinfarcts ( microscopic stroke ) in traumatic brain injury with loss of consciousness more than an hour.
These findings suggest that clinicians may be misdiagnosing late-life traumatic brain injury -related neurodegeneration as Alzheimer's disease, and therefore treatment targeting Alzheimer's would be ineffective in helping late-life decline among patients who experienced traumatic brain injury. Further work is needed to characterize post-traumatic brain injury neurodegeneration. ( Xagena )
Source: Mount Sinai School of Medicine, 2016