Thousands of people may be suffering tiny strokes that are damaging their brains but they aren't aware of the injury. That's the suggestion of a study to be published in the journal STROKE.

The study is based on American data that suggests that 18 per cent of those over the age of 45 may have suffered a tiny stroke called a "whispering stroke," which brings on mild symptoms that go unrecognized but that can still do damage to the brain.

"They are so small that they are only speaking softly to the participant," study author Dr. George Howard of the University of Alabama explained to CTV News. "It's not the devastating, knock you down on the floor, can't sleep, can't move kind of stroke."

Researchers in the U.S surveyed 21,803 participants and asked them whether they had ever had a 'whispering stroke,' a transient ischemic attack (a mini-stroke that creates symptoms that last only a few minutes) or whether they had experienced stroke-like symptoms but had not been diagnosed with a stroke or TIA.

The symptoms of a stroke include:

  • sudden weakness on one side of the body
  • sudden numbness
  • severe headache with no known cause
  • loss of vision
  • confusion or inability to speak

Compared to people with no history of stroke or TIA, people with stroke-like symptoms had a 5.5-point decrease on a scale of physical functioning, Howard's team found. They also had a 2.7-point lower score in mental functioning compared to those with no symptoms. That difference was greater than the decline observed in the TIA group (0.5) or the stroke group (1.6).

People who reported a history of inability to express themselves or understand language had larger current deficits in mental functioning.

"What we found was that people with these symptoms, despite the fact that they were never diagnosed with a stroke, actually have a substantial deficiency in their quality of life," says Howard.

Increased risk of dementia

With whispering strokes, patients recover quickly and the symptoms often go unreported. Nevertheless, there is injury to the brain, says Dr. Sandra Black, a neurologist at Sunnybrook Health Sciences Centre in Toronto.

"They are not innocent and they are affecting people's ability to do their normal activities," she says. 

"They predict the increase the risk of strokes in next four or five years, the increased risk of dementia. It's telling us that there is active disease in these people without them being aware."

Black says that anyone who suddenly experiences the signs of a stroke -- whether the symptoms clear up  or not -- should see a doctor.

"You have to take these short-lived neurological symptoms seriously. I'm not talking about 'I feel dizzy, I have a headache,I feel unwell.' I'm talking about an episode where people can't speak properly or are unable to understand or seem confused or are briefly paralyzed."

Doctors too should take reports of these symptoms seriously.

"If your patient comes and says, 'Last week, I couldn't express myself. I am doing fine now,' that may be an indication of something quite important that shouldn't be missed."

Dr. Michael Hill of the Heart and Stroke Foundation says there are times when mild neurological symtoms are not signs of a stroke. "But if you have high blood pressure or diabetes, or are a smoker, you are a person at risk. And if you have neurological symptoms, then it's more likely they are linked to strokeand you should get attention," he says.

High blood pressure and high cholesterol greatly increase the risk of stroke by weakening blood vessels that carry blood to major organs like the brain. Weakened vessels in the brain can rupture and that's what causes a stroke.

Black says the key is to make those who have had a whispering stroke aware that they have cardiovascular disease and need to make lifestyle changes.

"If we can change the future by having people be more aware, take more seriously that something may be injuring their brain, they are more motivated to keep their blood pressure under control, exercise, and get their cholesterol under control," says Black.