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How Head Injuries Seem To Affect The Risk For Stroke

The cause of strokes in younger people remains largely a mystery.

Twenty percent of strokes hit people under age 65, and the cause of many of those strokes remains a mystery. Having had a concussion or other traumatic brain injury might make the risk of a stroke more likely, a study says.

Back in 2011, researchers in Taiwan had unearthed an association between traumatic brain injury and stroke by combing through hospital records.

It's one of those "Oh, really?" findings that gets scientists itching to check it out themselves.

Researchers at the University of Michigan and the VA Center for Clinical Management and Research took on the challenge. The dug through billing records from emergency rooms in California from 2005 to 2009.

They found more than 436,000 people who had come to the ER with a traumatic brain injury. Those people were 30 percent more likely to have a stroke afterwards than people who hadn't had a traumatic brain injury. A little over one percent of them ended up having a stroke later on. The results were published online in the journal Neurology.

The researchers found that people under age 50 were more likely to have a stroke after a TBI than were people over 50. That said, the risk of stroke for someone under age 50 is low, so raising the relative risk by 30 percent has very little impact on an individual's risk.

Still, there are a lot of people out there who have had a concussion or other brain injury at some point in their lives.

To find out how much we should be concerned, Shots called up Dr. James Burke, the study's lead author and just days away from becoming an assistant professor at the University of Michigan. He says that when he saw the Taiwanese study he spotted some goofs in the methodology that he figured accounted for the finding. "I thought we would not find the same thing," he says.

So he was surprised to find an association between TBI and stroke in the California data, and even more surprised to find that it persisted despite efforts to find other reasons.

"I think the association's real," Burke told Shots. "The question is, what does it mean?"

What it doesn't necessarily mean is that TBIs cause strokes, or even increase the risk of stroke. It may be that people who have TBIs are already in poor health, or that their general health declines after the brain injury, increasing stroke risk.This study couldn't measure that.

If TBI does turn out to increase stroke risk, the most plausible reason would be that the TBI injures blood vessels in the brain, making them more vulnerable. The increased risk was found in ischemic stroke, which is caused by a blood clot blocking a vessel in the brain.

People who have had a concussion or other brain injury shouldn't fret, Burke says. Instead, they should do what we should all do: reduce stroke risk by maintaining a healthful blood pressure, and be aware of stroke warning signs, since immediate treatment of ischemic stroke with a clot-busting drug greatly reduces the risk of disability and death.

Copyright 2013 NPR. To see more, visit www.npr.org.

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