Without any warning, your mind could be at risk.
A stroke can be dramatic—and devastating. As part of the brain is starved of its blood supply, cells may die. If a large number of brain cells die, with them may go some of a person's ability to speak, move, and remember.
Yet there is also another type of stroke—one that is far subtler and harder to spot. Termed a "silent stroke," it creates areas of damage in the brain. These areas of dead brain cells are smaller than with a traditional stroke and they impact less-functional areas of the brain, but researchers are finding that they can still have a significant and lasting impact on memory.
Silent strokes are actually far more common than strokes with symptoms. For every person who has a stroke with symptoms, about 14 others have a silent stroke. Researchers estimate that more than one-third of people over age 70 have had a silent stroke.
As seen on this MRI, a silent stroke involves small spots of damage to areas of the brain that are not directly associated with functions such as vision or speech. Yet researchers are finding these strokes can have an impact on memory.
What is a silent stroke?
During a typical ischemic stroke, a clot blocks a blood vessel that feeds part of the brain. Without blood, cells in that area malfunction and may die, causing symptoms such as numbness or weakness on one side of your face, trouble speaking, difficulty walking, or vision problems, which reflect the functions that were controlled by the affected part of the brain.
During a silent stroke, an interruption in blood flow destroys areas of cells in a part of the brain that is "silent," meaning that it doesn't control any vital functions. Although the damage will show up on an MRI or CT scan, it's too small to produce any obvious symptoms. "A blood vessel can get blocked off, the tissue supplied by that vessel can die, but the person doesn't experience symptoms so they don't know they've had a stroke," explains Karen Furie, associate professor at Harvard Medical School and director of the Massachusetts General Hospital Stroke Service.
Most people who've had a silent stroke have no idea it occurred. "That doesn't mean it's insignificant, though," Dr. Furie says. Silent strokes can cause subtle signs, such as cognitive impairment, she adds.
Silent strokes and your memory
Though a woman may not notice any immediate effects, a silent stroke could interrupt the flow of information in her brain needed for memory, especially if several of these strokes occur over time (which is the most common scenario).
In a study published in the January 3 issue of the journal Neurology, researchers looked at more than 650 people without a history of dementia. Using MRI scans, the study authors tracked interruptions in blood supply to the participants' brains. More than 170 of the participants were found to have small areas of dead tissue from a lack of blood supply (called infarcts) in the brain, even though only 66 of them reported having had symptoms of a stroke. People with these brain infarcts had difficulties with memory and mental processes (cognition). The memory issues occurred independent of any shrinkage of the hippocampus (the part of the brain responsible for memory)—which is typically seen with Alzheimer's and other forms of age-related memory loss.
Researchers say that over time, the damage from silent strokes can accumulate, leading to more and more memory problems. "The more brain damage or injury that you have due to these silent strokes, the more difficult it is for the brain to function normally," Dr. Furie says.
What happens during a stroke
During a regular ischemic stroke, a clot interrupts the flow of blood to part of the brain. Without oxygen-rich blood, that part of the brain dies, taking with it functions such as speech and movement.
Being proactive about stroke prevention
The big question is: if a stroke comes without any symptoms and it can only be seen on an MRI or CT scan, how do you know you've had one, and what, if anything, can you do about it?
"I don't think it would be cost effective for everybody to have an MRI scan," Dr. Furie says. However, she adds, silent strokes "should make people aware that it's imperative to manage risk factors." Those risk factors include:
To lower your stroke risk, your doctor may recommend lifestyle changes (see box), or prescribe medicine to prevent a stroke, such as a drug that prevents blood clots from forming (such as Coumadin, aspirin, or others) or a cholesterol-lowering statin drug.
If you're experiencing signs of memory loss, don't dismiss them as a normal part of aging. See your doctor for testing. It's also important to let your doctor know if you have a family history of memory loss and stroke.
Because they live longer, women are more vulnerable to stroke, "so it is very important that they be aware that they're at risk, and make sure they've had an evaluation for vascular risk factors and cerebrovascular disease," Dr. Furie advises. "Women need to be very proactive about making sure that's addressed in the course of their routine medical exams."
Preventing memory loss from silent strokes
The good news is that silent strokes are a preventable form of memory loss. To avoid a silent stroke and protect your memory, follow these lifestyle tips:
Control your blood pressure by getting it checked regularly and taking blood pressure medicine, if you need it.
Limit salt to less than 1 teaspoon per day and follow the DASH eating plan, which has been shown to lower blood pressure about as much as medication in some people. (To learn more about this diet, visit: www.dashdiet.org/)
Aim to keep your total cholesterol levels below 200 mg/dL, and your LDL cholesterol below 100 mg/dL. To help lower your cholesterol, lose weight if you're overweight, consume less than 200 milligrams of cholesterol daily, and increase the fiber in your diet (20 to 30 grams of fiber each day is ideal).
Quit smoking. Smoking more than doubles your risk of a stroke. Talk to your doctor about nicotine-replacement products such as patches and gums, and medicines to help you quit.
Watch your weight. Aim for a body mass index between 19 and 25 (calculate your BMI at http://www.health.harvard.edu/topic/BMI-Calculator).
Eat at least 1.5 cups of fruit and 2.5 cups of vegetables a day and cut back on foods like red meat and sweets to keep your weight within a healthy range.
Play tennis, swim, ride a bike, or take a brisk walk for 30 minutes a day, at least five days a week. A 2011 study in the journal Neurology found that getting regular, moderate to intense exercise can cut your risk of a silent stroke by 40 percent.