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Both research and anecdotal evidence suggest a link between COVID-19 and increased risk of stroke, a phenomenon that emergency department physicians and neurologists began reporting within weeks of the coronavirus outbreak in the United States. Some patients came to the hospital because of a stroke and tested positive for COVID-19, and others had a stroke after being admitted for the virus.

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While risk of stroke is related to other infections such as influenza and severe bacterial infections, it seems to be higher with COVID-19—possibly as much as seven times higher among COVID-19 patients than among those with flu, according to a July 2020 study in JAMA Neurology. The increased risk may be related to an immune reaction and increased inflammation, both of which are linked to the clotting system. When inflammation leads to a clot that can trigger a stroke, it's called thrombo-inflammation.

Strokes affect about 1 to 3 percent of hospitalized COVID-19 patients, who are a small fraction of COVID-19 patients overall. The risk increases to 5 to 6 percent for patients in intensive care units. Worldwide, reports show that young, relatively healthy people can have strokes even without typical symptoms of COVID-19 like fever, cough, and loss of taste and smell.

Certain characteristics of coronavirus-related strokes have been documented, including blood clots appearing in unusual locations (the carotid artery, for one) or reappearing after they've been removed. This suggests the virus causes an increased tendency of blood to clot. Some patients have experienced large strokes, which affect the major blood vessels to the brain and can result in loss of speech and paralysis. Others have had multiple small strokes, which affect tiny blood vessels throughout the brain. The latter might be due to abnormalities in small blood vessels, perhaps provoked by the virus' ability to bind to the lining of the vessels. Bleeding in the brain, or hemorrhagic strokes, have been reported less frequently, and usually in critically ill patients.

Studies have shown that COVID-19 patients who have strokes are more likely to die than stroke patients without COVID-19. It could be because the immune response to the virus can cause a serious inflammatory condition called a cytokine storm, which increases the risk of stroke and damage to other organs, ultimately leading to death.

Strokes are treated the same whether they are related to COVID-19 or not. Patients may receive clot-busting medication; thrombectomy, which involves mechanically pulling the clot out of the vessel; or cholesterol-lowering drugs, such as statins. Recovery from stroke is also similar for those infected with the coronavirus and those who are not infected. Some evidence suggests that if hospitalized COVID-19 patients are prescribed blood thinners soon after admission, it may lower their risk of blood clots and subsequent stroke, but this has not been corroborated by clinical trials.

If you or someone you know is experiencing symptoms of a stroke, call 911 immediately. Although people might be reluctant to seek emergency help or go to the hospital during the pandemic for fear of contracting COVID-19, the hospital is still the safest place to be for somebody having a stroke. For this very reason, the American Heart Association created Don't Die of Doubt, a community education program that reminds people to call 911 and explains the FAST acronym for recognizing and responding to stroke symptoms: F, face drooping; A, arm weakness; S, slurred speech; and T for time to call 911 if someone has any of these symptoms. Other signs of stroke include severe headache, dizziness, sensory or visual loss, and sudden confusion.

Dr. Elkind is president of the American Heart Association. He is also professor of neurology and epidemiology and chief of the division of neurology clinical outcomes research and population sciences at Columbia University in New York.

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