It seems like practically every week now, researchers are learning some strange new detail about the novel coronavirus. The only thing that’s clear is how it affects people differently: Some are asymptomatic and don’t even realize they’re sick. Other have mild symptoms. And an unlucky 19% (according to one comprehensive study) are hospitalized with serious or even deadly complications, such as pneumonia, cardiac injury, and/or respiratory failure. Additional reported side effects range from diarrhea and loss of smell to swollen toes.
Now add to that list abnormal blood clotting and stroke. A series of reports published in leading journals document a small number of COVID-19 patients—all younger adults—who had strokes from blood clotting, with many not considered to be high-risk for serious illness. Some patients reported mild viral symptoms in the days prior to having a stroke, while others showed no noticeable COVID-19 symptoms at all—and didn’t even know they were sick.
“We are still in the learning phase of this disease,” says Rashid Chotani, M.D., vice president for medical affairs at CareLife Medical in Fairfax, VA, noting that researchers are still studying why and how such clotting occurs.
Still, these developments may change the approach to treating people with COVID-19, both in the hospital and at home. Here, we’ll break down what doctors know so far.
How frequently is this happening?
To date, the total number of stroke cases remains low, although reports are accumulating. On April 28, the New England Journal of Medicine documented five cases of severe stroke occurring in COVID-19 patients younger than 50 years old at Mount Sinai Health System in New York City. One patient, a 33-year-old woman, reported experiencing mild coronavirus symptoms—cough, headache, and chills—the week prior. Over a period of 28 hours, she began losing speech and developing numbness in her left arm and leg.
After initially delaying hospital care due to coronavirus fears, she did eventually seek treatment. Doctors discovered she’d had a stroke as a result of blood clotting in her brain. She received emergency intervention and was discharged to a rehabilitation facility.
Within a two-week period, the same study noted, the Mount Sinai Health System saw an additional four patients in their 30s and 40s who had large-vessel strokes, and who all tested positive for COVID-19. Large-vessel strokes, or occlusions (LVOs, the deadliest kind of stroke) occur when a blockage affects a major artery in the brain, cutting off significant blood flow. In two of these five cases, the patients presented with no other symptoms consistent with the coronavirus. Both arrived at the hospital with stroke symptoms only—although one 37-year-old male did have a known exposure to a family member with COVID-19.
Thomas Oxley, M.D., a principal author of the Mount Sinai report, summed it up to CNN on April 22, confirming a seven-fold increase in sudden strokes in younger adults over a two-week period in April. “Most of these patients have no past medical history and were at home with either mild symptoms—or in two cases, no symptoms—of COVID,” he told the outlet. At the time of the report’s release, all five patients survived.
NEW: A May 20 study that was led by researchers at NYU Grossman School of Medicine followed 3,556 COVID-19 patients in New York City and Long Island and found that fewer than 1% of those hospitalized with the virus also had a stroke—a figure 4% lower than similar stroke tallies in China. However, while less frequent, these strokes appear to be more serious. Researchers found that patients in the study who had strokes during a COVID-19 infection were younger, suffered worse symptoms, and were seven times more likely to die than other stroke patients without the virus.
Is this a larger trend being seen elsewhere?
Oxley and the report’s other co-authors point to data from Wuhan, China, that revealed how 5% of hospitalized COVID-19 patients had had strokes. A separate study of Irish patients, published on April 30 in the British Journal of Hematology, found that COVID-19 is associated with abnormal blood clotting, called coagulopathy, which results in a significant increased risk of heart attacks and strokes. Interestingly, in the Irish study, the most common type of blood clotting was noted within the lungs—appearing as hundreds of tiny “micro-clots” that could potentially block oxygen flow in the bloodstream.
An April 28 Science article goes further, speculating that such micro-clotting in the lungs could be the cause of yet another emerging—and puzzling—condition among critically ill COVID-19 patients: silent hypoxia, where blood oxygen levels are life-threateningly low, yet the patient shows no outward sign of struggling to breathe.
Reports like this are becoming so widespread that a May 1 report in the Canadian Medical Association Journal found that 20% to 55% of hospitalized COVID-19 patients are experiencing coagulopathy. And clotting problems can occur anywhere in the body. You may have heard the story of Nick Cordero, a Broadway actor whose right leg was amputated in April after blood clots kept forming there. Cordero, who was placed in a medically induced coma during the worst of his coronavirus battle, was put back on a breathing tube on May 1, with doctors saying they were hopeful about his prognosis. Still, while he has since opened his eyes, he is not yet responsive, according to various reports.
Are there theories about why blood clotting occurs?
Researchers are scrambling to understand what’s at the root of these troubling new symptoms. The leading theories include:
Blood-clotting could be caused by the body’s immune response.
It’s not a new phenomenon to see blood-clotting complications with viruses or bacterial infections. In fact, during the SARS outbreak from 2002 to 2004 in Singapore, large-vessel strokes were reported in a number of patients. Dr. Chotani notes three other viruses notably associated with strokes: varicella zoster virus (VZV), human immunodeficiency virus (HIV), and cytomegalovirus (CMV).
Dan Diekema, M.D., director of the division of infectious diseases at University of Iowa Healthcare in Iowa City, IA, explains how this viral-driven blood-clotting works. “Inflammation triggered by infection can lead to clotting abnormalities,” he says, like the formation of blood clots or a tendency for bleeding. When we get an infection, the body kicks into high gear with an inflammatory response to control it. In some cases, blood cells clot in an effort to trap the invader, preventing it from spreading further throughout the body. But sometimes those clots can break loose, travel to narrower vessels, and lead to worse problems—cutting off blood flow to crucial areas like a limb, or even the heart or brain. “It’s really thought to be an adaptive immune response, but like in many conditions, the immune response can also be pathologic or cause more harm perhaps than benefit,” Dr. Diekema explains.
This could simply be a direct effect of COVID-19’s disease course.
While blood clotting in COVID-19 patients is likely caused by the body’s immune reaction, it could also be a direct effect of the virus, according to Dr. Chotani. “It is not clear exactly how there is clotting in COVID-19 patients,” he says. ”It could be from the infection itself.”
An underlying, unknown condition could put some patients at higher risk.
Of course, it’s possible the documented patients were at higher risk of blood clotting than most, even if they didn’t realize it. “There are some genetic conditions that can cause people to have a higher propensity to develop blood clots,” Dr. Diekema explains. That’s not to say that only people with these genetic predispositions can get blood clots—and thus far, there have been no studies linking COVID-19 stroke patients to abnormal clotting conditions.
A major challenge with COVID-19 is that it’s a new virus, so researchers still have plenty learn about its effects in the body. “We don’t know as much as we’d like, because most of the information is from case series at this point,” Dr. Diekema says, and not from widespread studies of thousands of patients, which would give researchers a broader picture of why and how such clotting occurs.
How might this affect COVID-19 treatment?
As more reports of blood clotting in COVID-19 patients emerge, researchers have begun looking into new avenues to treat patients.
Dr. Diekema notes one major question on many doctors’ minds. “Should we increase the amount of anti-coagulation [blood thinner] that we give to COVID-19 patients?” In most U.S. hospitals, patients who are bedridden are given something called thromboprophylaxis, a low dose of blood thinner to prevent clotting from sitting in a hospital bed all day. Typically, higher doses of blood thinner would be reserved for patients who already have a clot, but it could potentially be used as a preventative measure before any clots appear.
People with milder symptoms, who do not require hospital treatment for COVID-19, could potentially be prescribed a blood thinner if it proves be helpful, Dr. Diekema adds. “These questions are not yet answered, but there are studies starting up now to get to the bottom of whether those provide any benefit.”
In a pre-proof letter in the Journal of the American College of Cardiology, accepted on April 15, Behnood Bikdeli, M.D., notes that blood thinners could increase risk of dangerous excess bleeding, so healthcare providers should proceed with caution in administering this type of treatment to COVID-19 patients. A joint study from the Massachusetts Institute of Technology in Cambridge and the University of Colorado at Denver is currently testing a blood-thinning drug called tissue plasminogen activator (tPA) in COVID-19 patients with severe respiratory distress, with the potential to scale up this treatment if it helps save lives.
What do these developments mean for you?
Until researchers have a clear handle on what’s causing abnormal blood clotting, there may not be a lot you can do to lower your risk of it happening to you, should you contract COVID-19. But one thing you can do is monitor your symptoms closely and continue to follow CDC guidelines for social distancing to avoid exposure to the virus.
So, think back to the Irish study that linked low oxygen levels to blood clotting in the lungs, and the phenomenon known as silent hypoxia. With that condition, patients are still able to speak normally and move around on their own—and don’t complain of shortness of breath. “These patients do not have a sensation of breathing problems, although chest X-ray shows pneumonia, and their oxygen saturation level is way below normal,” Dr. Chotani explains.
This silent hypoxia effect is just beginning to be reported in studies and op-eds from medical doctors, causing some to suggest that pulse oximeters might be used at home to monitor oxygen levels before other, obvious symptoms develop. A pulse oximeter is a small device that can tell you your oxygen saturation level and pulse rate, simply by placing a finger inside a sensor. You can buy one online to use at home, but Dr. Chotani emphasizes the importance of allowing a doctor to interpret the data. “People using it at home must consult with their primary care physicians,” he says. “Not doing so and not understanding what the saturation level and pulse readings mean can drive many people to the emergency room” if they misinterpret the device’s results.
However, should you begin to experience stroke symptoms—for any reason—remember the acronym FAST:
- Face drooping
- Arm weakness
- Speech difficulty
- Time to call 911
Then, don’t hesitate. Call for an ambulance immediately. The sooner you get to the hospital the better your long-term prognosis will be.
Whether blood clotting and stroke will emerge as significant symptoms of COVID-19 remains to be seen. In the coming weeks and months, we’re sure to learn more about such complications—and, even better, how to both avoid and treat them.