medwireNews: Traumatic brain injury (TBI) with loss of consciousness is associated with an increased risk for neurodegenerative conditions, but Alzheimer’s disease (AD) is not one of them, suggests research.
The study of 7130 individuals, aged an average of 80 years, from three prospective cohort studies found no increased risk of mild cognitive impairment, AD or dementia among the 865 who had a history of TBI with loss of consciousness. This was despite 1537 cases of dementia and 1322 of AD being identified over 45,190 person–years of follow-up.
“To our knowledge this study is by far the largest ever on this topic. With more than adequate power to detect an association between TBI with [loss of consciousness] and AD, we found none”, the researchers comment in JAMA Neurology.
However, there was a strong association between TBI with loss of consciousness and Parkinson’s disease (PD), of which there were 117 cases over follow-up. This was particularly the case for patients who had lost consciousness for more than an hour (142 individuals).
The hazard ratio for incident PD from the Adult Changes in Thought (ACT) study was a significant 3.56 for patients with TBI and loss of consciousness for more than an hour, while combined data from the Memory and Aging Project (MAP) and the Religious Orders Study (ROS) showed a significant 1.65-fold increase in the risk of parkinsonian progression among TBI patients with loss of consciousness for less than an hour and 2.23 with loss of consciousness for more than hour.
Neuropathological data from autopsies carried out on 1589 individuals supported the clinical findings.
TBI was not associated with beta amyloid plaques or neurofibrillary tangles, common markers of AD, but it was associated with a significant 1.59-fold increase in the risk of Lewy bodies in the frontal or temporal cortex with loss of consciousness for less than an hour and a 1.58-fold increase in cortical microinfarcts with loss of consciousness for more than an hour.
The researchers, led by Paul Crane (University of Washington, Seattle, USA), note that nearly half of the TBI cases with loss of consciousness for more than an hour occurred before the age of 25 years.
And for these individuals the risk of microinfarcts and Lewy bodies, especially in the frontal or temporal cortex, increased further to 1.66-fold, 1.86-fold and 2.53-fold, respectively.
“Traumatic brain injury with [loss of consciousness] sustained early in life is not innocuous and appears to be associated with neurodegenerative conditions, although not AD”, the team comments.
They acknowledge that there is a lot of interest in the effects of repetitive TBI, but the number of patients in their study with more than one TBI was too small for analysis.
By Lucy Piper
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