A silent stroke, also known as a silent cerebral infarct, is a stroke that does not result in the typical symptoms of a regular stroke, like sudden weakness, numbness, or speech problems. Despite not causing noticeable symptoms, silent strokes still damage brain cells. Here is an overview of silent strokes, their causes, symptoms, and treatment.
What is a silent stroke?
A silent stroke occurs when a blood clot blocks blood flow to the brain or a blood vessel in the brain ruptures, causing brain cell death. However, the area of the brain affected is small enough that there are no immediately noticeable symptoms. Despite the lack of symptoms, brain cells still die from the lack of blood and oxygen.
Silent strokes are also sometimes called silent cerebral infarcts or silent brain attacks. “Silent” refers to the lack of obvious symptoms compared to a regular or “overt” stroke. An “infarct” means an area of dead tissue due to a blockage of blood supply.
What causes a silent stroke?
A silent stroke is caused by the same mechanisms as an overt stroke – either a blood clot blocking blood flow to part of the brain or a blood vessel rupturing and preventing oxygen from reaching brain cells. However, in a silent stroke, the part of the brain affected is smaller.
Some of the most common underlying causes and risk factors for silent stroke include:
- High blood pressure – can lead to artery and blood vessel damage
- Cigarette smoking – causes blood vessel narrowing
- High cholesterol – can lead to blockages from atherosclerosis
- Diabetes – damages blood vessels
- Obesity – increases risk of high blood pressure and diabetes
- Sleep apnea – low oxygen levels may damage brain tissue
- Atrial fibrillation – irregular heartbeat allows blood clot formation
- Family history of stroke
- Being African American, Hispanic, or Asian
- Women have more silent strokes than men
Treating and preventing the above risk factors through lifestyle changes and medication can help prevent silent strokes from occurring.
How common are silent strokes?
Silent strokes are extremely common. Some estimates suggest 2 million people in the United States suffer from silent strokes each year. That’s about 5 times as many people who have overt strokes.
Up to 20% of people over the age of 65 have evidence of silent strokes when imaging is done of their brain. The prevalence increases with age.
Who is at risk of having a silent stroke?
Those at highest risk of having a silent stroke include:
- Older adults – Risk increases dramatically after age 65
- People with untreated high blood pressure
- Individuals with heart disease
- People with diabetes
- Those who smoke cigarettes
- People with high cholesterol
- Individuals with sleep apnea
- People with atrial fibrillation or flutter
- Those with family history of stroke
- African Americans, Hispanics, and Asians
The more of these risk factors someone has, the higher their risk of silent stroke. Adults over 65 with high blood pressure and diabetes are at very high risk.
Do silent strokes cause symptoms?
By definition, silent strokes do not cause any immediately obvious symptoms when they occur. You usually will not suddenly develop weakness on one side of your body, trouble speaking, paralysis, or numbness like you would with a major overt stroke.
However, although silent strokes do not lead to noticeable symptoms right away, they can cause very subtle symptoms that develop gradually over time. These include:
- Forgetting recent events or appointments
- Becoming lost in familiar places
- Difficulty following conversations
- Trouble understanding instructions
- Frequently losing items
- Developing weaker grip strength
- Becoming clumsy and unsteady on feet
- Vision changes or loss
- Altered mood or personality
These symptoms can often be chalked up to normal aging. But if they develop suddenly, silent strokes may be the cause.
How are silent strokes diagnosed?
Because they do not cause acute symptoms, silent strokes are most often discovered incidentally when brain imaging is done for other reasons. Brain imaging techniques like MRI or CT scans may pick up areas of dead brain tissue or small infarcts that point to past silent strokes.
Silent strokes may also be detected if you suddenly have cognition or physical abilities tests that reveal subtle declines in memory, thinking, or motor skills.
An MRI scan is the most sensitive test for picking up evidence of silent strokes. Your doctor may order this test if you have vascular risk factors and have developed mild but noticeable cognitive deficits or physical difficulties.
Do silent strokes show up on MRI?
Yes, silent strokes will show up on an MRI scan of the brain. The MRI will detect small areas of dead brain tissue caused by an infarct or “silent stroke”. These small lesions in the brain are not visible on a regular x-ray or CT scan.
MRIs are considered much more sensitive than CT scans when it comes to detecting silent strokes. One study found that among people with no history of overt stroke, 17.6% of those over age 65 had evidence of silent stroke on MRI compared to just 6.7% on CT scan.
Are silent strokes dangerous?
Yes, silent strokes can be dangerous in the long run. Each silent stroke kills brain cells and damages your brain. Although they do not cause immediate disability like a major stroke, over time the accumulative effects can lead to cognitive decline, dementia, and impaired physical functioning.
People who have silent strokes also appear to be much more likely to eventually have an overt stroke. One study found that 36% of those found to have silent strokes on MRI scans went on to have an overt stroke within 4 years.
Do silent strokes turn into full strokes?
Silent strokes themselves do not turn into full strokes. The danger is that people who have had silent strokes appear to be at much higher risk of going on to have an overt stroke down the road compared to the general population.
In one study, people with evidence of silent strokes on MRI scans were 5 times more likely to go on to have a major overt stroke within the next 5 years compared to people with normal MRI scans.
Do silent strokes go away?
No, the brain damage caused by a silent stroke does not go away on its own. The area of infarcted or dead brain tissue caused by a lack of oxygen will remain. However, the brain does have some ability to reorganize and regain some lost function through forming new connections between neurons.
What is the treatment for silent stroke?
There is no direct treatment for brain tissue already damaged by silent strokes. However, steps can be taken to prevent new silent strokes from occurring and to manage symptoms.
Treatment focuses on controlling any underlying medical conditions that may have led to silent strokes, primarily:
- Hypertension – Keeping blood pressure well-controlled through medications like ACE inhibitors or diuretics
- Diabetes – Maintaining good blood sugar control through insulin, oral medications, diet, and exercise
- High cholesterol – Using statins or other lipid-lowering drugs
- Atrial fibrillation – Taking blood thinners to prevent clots from forming
- Sleep apnea – Using CPAP machine at night
Quitting smoking and maintaining a healthy weight through diet and exercise are also important.
Physical, occupational, and speech therapy may help regain lost abilities or teach ways to compensate for any disabilities.
Can silent strokes be prevented?
Yes, although they cannot be completely prevented in all people, the risk of silent strokes can be dramatically reduced by controlling underlying medical conditions associated with them, including:
- Treating high blood pressure (anti-hypertensive medications)
- Keeping diabetes under control (insulin, oral meds, lifestyle changes)
- Lowering high cholesterol (statins, lifestyle changes)
- Preventing atrial fibrillation when possible (anti-arrhythmic meds)
- Using CPAP for sleep apnea
- Stopping cigarette smoking
- Losing weight if obese or overweight
- Following a heart-healthy diet
- Getting regular physical activity
The key is to control any major stroke risk factors. This requires following up regularly with your doctor for monitoring and being compliant with any prescribed medications.
What percentage of strokes are silent?
It is estimated that silent strokes may account for 20% of all strokes. However, the exact percentage is difficult to determine because they do not always cause symptoms that lead to medical attention. Their incidence appears to be many times higher than that of overt strokes.
Can you recover from a silent stroke?
The brain damage done by a silent stroke cannot be reversed. However, some recovery is possible through neuroplasticity, which is the brain’s ability to reorganize itself by forming new connections between neurons. With rehabilitation, people can regain some lost function.
Controlling risk factors for stroke can also prevent further silent strokes, which allows the best possible recovery by avoiding more damage to the brain.
Conclusion
Silent strokes are small strokes that do not result in acute symptoms but still damage brain tissue. They are caused by the same mechanisms as overt strokes but affect a smaller area of the brain. The accumulative effects of multiple silent strokes can lead to dementia and disability. However, controlling medical conditions that put people at risk allows prevention of further silent strokes.