'Silent strokes' leave traces on brain, up risk for full-blown stroke, dementia

Dr. Gustavo Saposnik, neurologist at St. Michael's Hospital in Toronto is shown in this undated handout image. Silent strokes are common as people age. About seven per cent of people in their 50s have silent strokes. (THE CANADIAN PRESS/HO-St. Michael's Hospital)

TORONTO -- Peter Chaban was up early doing dishes one morning in 2012 when he noticed there was water flowing over his hand -- but he couldn't feel it. Next thing he knew, he lost all sensation and strength on his left side and dropped to floor. Within seconds he was lying there completely immobilized.

By the time the ambulance arrived at his vacation property near Collingwood, Ont., Chaban had recovered, but doctors at the local hospital diagnosed him with a probable transient ischemic attack, or TIA, a type of temporary stroke that leaves no permanent damage.

Once he returned home to Toronto, Chaban was sent for an MRI, and the brain scan confirmed that diagnosis. But of more concern was the discovery of "quite a few" lesions in his brain, the result of "silent strokes," which show up as small holes on imaging.

When they had occurred and over what time period was a mystery to Chaban, who had experienced no symptoms.

That's why, in fact, they're known as silent -- patients have no idea they've had a miniature clot or microbleed in the brain that has destroyed a tiny chunk of neurons, but resulted in no loss of function as would typically occur with a full-blown stroke.

"I was never aware of any deficits," said Chaban, 64, who retired from his research job at the Hospital for Sick Children three years ago. "When I was employed, I was quite cognitively active.

"I was physically very active. I ski, play golf, I played squash until a few years ago. And my health is very good, so the silent strokes hadn't expressed themselves, at least to my awareness."

Silent strokes are common as people age. About seven per cent of people in their 50s have silent strokes. That figure rises to about 15 per cent for those in their 70s. And among people aged 80-plus, about one-quarter have unknowingly been affected.

Researchers estimate that for every symptomatic stroke, there are up to 10 silent strokes within the population.

Dr. Gustavo Saposnik, a neurologist at St. Michael's Hospital in Toronto, said the discovery that a patient has had one or more silent strokes is serendipitous -- their doctor may have ordered a CT or MRI for an unrelated reason and the scan turned up the lesions.

While they may not cause any functional impairment, silent strokes are still concerning, he said, as they increase the risk of suffering a full-blown stroke in the future.

Their occurrence doubles or triples a person's odds of having a symptomatic stroke and the potential disabilities that can result -- from full or partial paralysis on one side of the body and diminished sensation to impaired speech and cognitive deficits.

The American Heart Association and American Stroke Association recently published the first set of guidelines to help doctors manage patients with the telltale signs of a silent stroke found on a brain scan, with a primary focus on preventing a future symptomatic stroke.

"One of the considerations is that if blood pressure is not under control ... these may well happen," Saposnik said of silent strokes, adding that high cholesterol, diabetes and smoking are other risk factors.

Neurologist Dr. Eric Smith, who chaired the group of international experts who wrote the AHA-ASA guidelines, said taking steps to prevent silent strokes also may pay off in reducing the risk for dementia.

"Because when you start to collect these silent strokes, they start out silent. But if you get too many of them they can also cause problems with memory and thinking," said Smith, medical director of the cognitive neurosciences clinic at the University of Calgary.

"So it's not uncommon to do a scan on somebody who complains of memory problems and see they've had some silent strokes.

"But we know these silent strokes -- they don't stay silent. They mark people at risk for the bigger ones and for cognitive decline and dementia too."

For Chaban, learning that he had signs of silent strokes was "quite sobering," and he decided he needed to take better care of his health.

"I guess the positive side of this is I'm much more conscientious about keeping my blood pressure down, of eating properly," he said, noting that he now takes a drug to keep his cholesterol levels in check.

Had he not suffered the TIA, he wouldn't have known about the silent strokes that had left their signatures on his brain and put him at potential risk for much worse, Chaban said.

"My bad luck turned out to be good luck."