Traumatic bangs on the head can cause changes in the brain that are a hallmark of Alzheimer's, a study has found.
The early and small-scale research does not confirm a link between brain injury and dementia, but raises the possibility that one exists.
Scientists studied nine people with an average age of 44 who had suffered a single moderate to severe traumatic brain injury (TBI) between 11 months and 17 years ago.
Brain scans showed that, like Alzheimer's patients, their brains contained clumps of beta amyloid protein. Individuals who had sustained more damage to nerve fibres in the brain had more of the clumps, or "plaques".
However, only people who had suffered head injuries had beta amyloid plaques in the cerebellum brain region.
Lead researcher Professor David Sharp, from Imperial College London, said: "The study is small and the findings preliminary. However, we did find an increased build-up of amyloid plaques in people who had previously sustained a traumatic brain injury.
"The areas of the brain affected by plaques overlapped those areas affected in Alzheimer's disease, but other areas were involved.
"People after a head injury are more likely to develop dementia, but it isn't clear why. Our findings suggest TBI leads to the development of the plaques which are a well-known feature of Alzheimer's disease."
The research, published in the journal Neurology, suggests that a different mechanism from that typically seen in Alzheimer's can lead to the formation of amyloid plaques after traumatic brain injury.
"The damage to the brain's white matter at the time of the injury may act as a trigger for plaque production," said Prof Sharp.
"If a link between brain injury and later Alzheimer's disease is confirmed in larger studies, neurologists may be able to find prevention and treatment strategies to stave off the disease earlier."
