Traumatic brain injuries with loss of consciousness do not seem to increase the risk of Alzheimer's later in life, but did elevate the odds of developing Parkinson's.
A large, multi-institution study has found no connection between suffering a traumatic brain injury with loss of consciousness and later development of Alzheimer’s disease or dementia. Even when participants reported loss of consciousness lasting more than an hour after sustaining such an injury, they were at no greater risk for dementia later in life.
Crane and colleagues looked for connections between traumatic brain injury and late-life development of neurodegenerative conditions—such as Alzheimer’s and Parkinson’s or parkinsonian features—and brain abnormalities discovered at autopsy. These can include plaques and tangles common in Alzheimer’s disease;
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A Lewy body in a sample of brain tissue.
protein clusters called Lewy bodies that are often seen in Parkinson’s disease; and small areas of brain cell death called microinfarcts.
"To our knowledge this is by far the largest study ever on this topic,” Crane said. “Several previous studies have suggested associations between TBI [traumatic brain injury] with loss of consciousness and Alzheimer’s disease. We had ample ability to find this same kind of connection, as hundreds of participants in this study ended up developing dementia or Alzheimer’s disease. But we didn’t find one."
Interestingly, the new findings did suggest that traumatic brain injury with loss of consciousness was linked with late-life development of Parkinson’s disease, the progression of parkinsonian features over time and the development of Lewy bodies. The researchers also found that people who were 25 years old or younger when they experienced a traumatic brain injury with loss of consciousness were more prone to developing Lewy bodies and microinfarcts.
These findings combined suggest an interesting “time capsule effect” as Crane called it. This is where someone sustains a traumatic brain injury and seemingly returns to normal functioning. Yet some 40-plus years later Parkinson’s or parkinsonian features emerge.
The researchers analyzed data from three separate studies that began in the 1990s. They followed participants until they developed dementia, dropped out, or died. Of the 7,130 people enrolled, 865 reported a traumatic brain injury combined with loss of consciousness. Of these, 142 reported being unconscious longer than an hour.
Crane collaborated with UW Medicine colleagues as well as researchers from Mount Sinai School of Medicine, Cleveland Clinic Foundation, University of Utah and Rush University Medical Center. Eric Larson, executive director of the Group Health Research Institute in Seattle, was senior author for the study.
The study was funded by these grants from the National Institutes for Health: U01 AG006781, U01 NS086625, P50 AG005136, P50 NS062684, K01 HD074651, P30 AG10161, RF1 AG015819, R01 AG17917, R01 AG22018, R01 AG042210, and R01 NS78009. Additional support was received from the Paul Allen Family Foundation.