How Many Hits to the Head Before Dementia-Like Damage Occurs?

By | August 1st, 2018

How many hits can a person take before a blow to the head translates to damage that mimics dementia? Just one, according to new research published in the journal Brain.

Researchers found that a single blow to the head could lead to the increased production of tau proteins, one of the hallmarks of Alzheimer’s disease.

The researchers looked at the brains of 15 people who had moderate to severe brain injuries from things like car crashes, assaults, or other types of accidents. The people all lived for up to 18 years after their injury and had died from other causes. None of them were diagnosed with dementia, but their brains had tau like dementia patients—whereas brains the team examined that had never experienced an injury did not.

In a separate, but related part of the study, scientists examined mice with brain injuries. The mice had the same abnormal formations of tau at the site of the injury and throughout the brain.

“In parallel studies, we observed the same type of abnormal tau in injured mice, which, over time, spread from the site of injury to involve remote brain regions,” said Roberto Chiesa, an author of the study.

In a healthy brain, tau helps hold the cell structures together. But in brains with dementia, tau spreads across the brain abnormally and forms into what scientists call ‘tau tangles.’

Concerns have been raised over the risk involved in playing contact sports like football and rugby after several studies confirmed that it puts players at a higher risk of Chronic Traumatic Encephalopathy, or C.T.E. One study from Boston University found that of 111 brains of N.F.L. players autopsied, all but one had C.T.E, which causes symptoms like memory loss, depression, confusion and dementia.

A study earlier this year found that just one traumatic brain injury can double the risk of dementia. That study looked at over 350,000 U.S. veterans who sustained injuries in and out of service. For those with severe brain injuries, the rate of dementia was 9.8 percent. For those without a brain injury, the rate was 2.6 percent.

Another study found that even after decades have passed, a traumatic brain injury can raise the risk of dementia by up to 80 percent. While the risk drops as the years pass, after 30 years the risk for dementia in patients with an injury was still 25 percent greater than those who never experienced a brain injury.

“Traumatic brain injury is a leading cause of death and disability in young adults,” said Dr. Elisa Zanier in a statement, who led the Mario Negri Institute team. “Moreover, even in milder cases, it represents a risk factor for dementia, such as chronic traumatic encephalopathy.”

Zanier said that understanding how events like a brain injury from a single car crash trigger the same reaction in the brain that causes dementia could help uncover a therapy for both dementia patients and people with brain injuries.

This study was published in the journal Brain.

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