Mini-Stroke Linked to Increased Dementia Risk

When clinicians care for people who’ve had a TIA, their focus is typically on lowering the risk of a subsequent full-blown stroke, particularly in the days and weeks afterward, says the lead study author, Raed Joundi, MD, DPhil, a stroke neurologist, an assistant professor at McMaster University, and an investigator at the Population Health Research Institute in Hamilton, Ontario.

But helping patients avoid long-term cognitive issues should be an additional priority, the study suggests. “What we found is that dementia is also an important long-term complication,” Dr. Joundi says.

Study Tracked More Than 113,000 People for Up to 20 Years

For the study, researchers pulled two decades of health records from Ontario to identify more than 113,000 adults who’d had a first TIA and no history of dementia. The average age of study participants was 70.

Each person was matched by age, sex, and vascular risk factors like high blood pressure and diabetes to someone who hadn’t had a mini-stroke or stroke — and separately, to someone who’d had a first stroke.

The scientists tracked everyone for a new dementia diagnosis starting 90 days after their TIA, for an average of about 7 years and as long as 20.

Compared with people who hadn’t had a TIA, those who had one were more likely to develop dementia at every point researchers checked.

• About 19 percent of people with a TIA developed dementia during follow-up, compared with 15 percent of matched people without a TIA, and 20 percent of those who’d had a stroke.
• The risk of dementia after a TIA was 75 percent higher than in matched controls within the first year, and remained 34 percent higher over the full follow-up period.
• After a TIA, dementia risk started out lower than after a stroke, but the two posed roughly the same dementia risk within about five years.
• People who’d had a TIA were roughly three times more likely to develop dementia during follow-up than to have a second stroke.

This last finding is especially striking, says Joundi. “So when we think about preventing the long-term consequences of TIA, we should be thinking not only about preventing stroke, but also about preserving brain health and cognition,” he adds.

Why Might a Mini-Stroke Raise Dementia Risk?

Is there something about having a TIA that increases the risk of dementia, or could it be that the same risk factors that make a mini-stroke more likely also increase the likelihood of dementia?

The answer is probably some combination of both, says Joundi. “TIA and dementia certainly share many risk factors, including high blood pressure, diabetes, atrial fibrillation, and other vascular diseases,” he says.

“But importantly, we matched people with TIA to people of the same age and sex who had similar vascular risk factors and comorbidities, and there was still a substantial excess risk of dementia. That suggests that common measured risk factors alone do not completely explain the association,” says Joundi.

Later strokes didn’t explain the link either. “One thing we could show is that the association was not explained by people having strokes after the TIA,” Joundi says. While it did increase dementia risk, as expected, accounting for those strokes only minimally changed the association between TIA and dementia, he says.

“TIA may be both a marker of a brain prone to cognitive decline and potentially a contributor to subsequent brain injury, such as accelerating neurodegeneration,” Joundi says. More studies that look at what is actually happening in the brain are needed to disentangle those possibilities, he adds.

“The early separation [in the data] indicates the TIA itself might be the cause — some TIAs clinically may have unmeasured injury to the brain,” says Ken Uchino, MD, a neurologist at Cleveland Clinic in Ohio who wasn’t involved in the study. “But longer-term incident dementia may indicate vulnerability of the patient or their brain to dementia — maybe, despite risk factor matching, these individuals with TIA might have higher blood pressure and more risk factors for vascular dementia.”

Strengths and Limitations of the Study

The study’s size and length of follow-up are notable strengths, says Dr. Uchino, who called the methodology “well done.”

Because the study relied on medical billing and diagnostic codes rather than in-person cognitive testing or brain imaging, it couldn’t identify covert strokes or determine the specific type of dementia involved, and some people diagnosed with a TIA may have actually had a minor stroke or a look-alike condition, according to the authors.

When the researchers excluded people later diagnosed with a minor stroke, though, the association with dementia barely changed, says Joundi.

Still, the new research is an observational study, meaning it can show a strong association but can’t prove that a TIA directly causes dementia.

What to Do if You’ve Had a Mini-Stroke

Having a TIA does not mean that you are going to develop dementia, says Joundi.

“Most people in our study did not,” he points out. Still, he suggests treating a TIA as a warning sign for long-term brain health, not just future stroke.

His advice for lowering dementia risk:

• Work with your care team to keep blood pressure, cholesterol, and diabetes well controlled.
• Take any prescribed stroke-prevention medication consistently.
• Stay physically active.
• Avoid smoking.
• Follow a healthy diet.

Uchino also raises a bigger-picture question about potential issues with how our current healthcare system treats patients who’ve had a TIA.

Stroke care and dementia care are usually managed by different medical specialists, and better coordination between the two, or more clinics equipped to watch for cognitive changes after a TIA, could help catch problems earlier, he says.