The risk of another traumatic brain injury, however, more than doubled if the first injury occurred before age 25 and almost quadrupled if the injury happened after age 55. Similarly, a recent traumatic brain injury more than doubled the odds of death from any cause, the study found.
Dams-O'Connor's group plans to look at risk factors to try to understand why some people have poor long-term prognosis after a brain injury.
One expert said genetics may play a role. "My guess is that the risk for post-traumatic-brain-injury Alzheimer's disease has a genetic component with some genes increasing risk and others offering protection," said Dr. Sam Gandy, associate director of the Mount Sinai Alzheimer's Disease Research Center in New York City.
These findings should not be confused with those regarding athletes who suffer brain injuries, Gandy said.
"The dramatic examples of former [National Football League] players, hockey players and wrestlers who have an unusual illness, marked by depression, agitation and psychosis are quite different from Alzheimer's disease patients who tend to be apathetic," he said.
"Much remains to be discovered about the role of lifelong traumatic brain injury history, including severity and nature of torque and other physical factors, and late-life mental decline," Gandy said.
Another expert, Dr. Danny Liang, a neurosurgeon at North Shore-LIJ Cushing Neuroscience Institute in Manhasset, N.Y., thinks these findings are too narrow to say much about the risk of dementia as a result of traumatic brain injury.
"The study is restricted to a limited population so it's hard to extrapolate these findings to other populations," he said. "It is also possible that there were people who had traumatic brain injury who did develop dementia before age 65, so they were not included in the study," Liang said.
There also was no data on injury severity or durati
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