En español | Babak Navi, the division chief for stroke and hospital neurology at Weill Cornell Medicine and a neurologist at New York-Presbyterian, has been working on the front lines of the coronavirus pandemic in New York City for several weeks. And during that time, he's noticed a troubling pattern of symptoms beyond respiratory distress in patients with COVID-19, the illness caused by the new coronavirus.
Some have developed strokes; others have experienced seizures. A handful have woken up to slower-than-normal cognitive speeds. The common thread among these COVID-19 patients? All point to disruptions in the nervous system.
As the sum of coronavirus cases continues to climb, experts are learning more about the virus and the illness it causes. And an increasing number of reports from hospitals around the world show that in some patients, the disease can damage more than just the lungs. It can harm the brain, too.
A study in JAMA Neurology found that more than 36 percent of 214 patients in Wuhan, China, experienced neurologic symptoms during the course of their COVID-19 illness. Dizziness and headache were among the most common symptoms listed; instances of stroke and loss of taste and smell were also reported. Other published accounts document a more-than-usual prevalence in COVID-19 patients of Guillain-Barré syndrome, an affliction that can lead to temporary paralysis, plus instances of confusion and severe agitation.
"I think at this point, I would say that we know something” is happening when it comes to COVID-19 and the brain, says Sherry Chou, associate professor of critical care medicine, neurology and neurosurgery at the University of Pittsburgh. “But we definitely don't know enough.”
Among the biggest questions on her mind — and the minds of experts across the globe — are why and how the novel coronavirus produces neurological symptoms in some. Does it target the nervous system directly? Or is the brain merely a victim of the body's reaction to the infection?
"We're really in uncharted waters here,” Chou says, noting that most of what we do know about how the virus attacks the body is still anecdotal due to its newness and the current focus on care and containment. Chou is hopeful the gap in knowledge will soon narrow, however. She's leading a research consortium of physicians and scientists from around the world to better understand the virus’ impact on the brain and the nervous system.
"We need to figure out as quickly as we can, and as accurately as we can, how big a problem this is, how often is this happening, and who is it happening to,” Chou adds.
The virus vs. the immune system
One theory that's being floated in the scientific and medical communities is that the virus may enter the nervous system through the olfactory bulb, which sits just above the nasal cavity and transmits information from the nose to the brain. This could explain why many people with COVID-19 report a loss of smell or taste — signs of illness the Centers for Disease Control and Prevention (CDC) recently added to its list of COVID-19 symptoms.
"It's a nice-sounding theory,” Chou says — especially considering that “we know the coronavirus lives in your nose.” (Testing for virus is often conducted by way of a nasal swab.) But “there is currently no proof of that whatsoever,” she adds.
Another thought is that the body's reaction to the infection is what causes nervous system damage in some people with COVID-19. Sometimes when the body fights off an infection, “it's not the infection itself that hurts your brain and your nerves, but your body's response in trying to fight off that infection,” Chou explains. And that response “can actually hurt your brain and your nerves by mistake, almost.” Think of it as “friendly fire,” Chou says.
This type of reaction is not unique to COVID-19. When the body fights the virus that causes the flu, for example, an immune response can trigger dizziness and headaches, says Igor Koralnik, professor of neurology at Northwestern University's Feinberg School of Medicine. Headache is another possible neurological symptom of COVID-19 listed by the CDC.
Because difficulty breathing is common among people with moderate to severe cases of COVID-19, Koralnik points to the possibility that a primary infection could take place in the brain stem — particularly the part that houses the respiratory centers and controls breathing. An infection in this part of the nervous system “could further worsen the respiratory failure of the patient, if it was the case,” Koralnik says.
"So it's not clear if it's a direct infection by the virus or if it's secondary to the systemic inflammation that [a patient may have] due to dysregulated immune response to the virus,” he adds.
Injury to the brain and nervous system could also be a result of a cascade effect from loss of oxygen from damaged lungs that leads to multisystem organ failure, experts say. “The overall process of being critically ill” may also play a role in the development of neurological complications, Navi says.
Blood clots in COVID-19 patients increase stroke risk
Alex Spyropoulos, an internist and professor of medicine at the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell, has been studying people with blood clotting disorders “for a quarter of a century” and says COVID-19 is one of the most clot-causing diseases he's ever seen.
"The risk of blood clots are anywhere from about three- to sixfold more than we're used to seeing,” Spyropoulos says. “So it has us all in the academic community a little bit befuddled, because it's one of the most aggressive diseases with respect to blood clots that we've ever seen.”
These blood clots can lead to life-threatening conditions in people with COVID-19, including stroke. Early data from China and Singapore highlighted this complication, and now, a growing number of hospitals in the U.S. are starting to see and study this phenomenon.
As with other neurological events, experts are unable to pinpoint the exact cause of strokes in coronavirus patients. Navi speculates some are likely triggered by COVID-19's effects on the body's clotting system, while others may be due to the severity of illness, since “critical illness and severe infections do predispose” a person to stroke.
Advanced age and underlying health conditions may also be at play. Both increase one's risk for stroke, according to the CDC. This population is also more likely to experience severe illness from a coronavirus infection.
"So it's a combination of a lot of things. But we know that patients with underlying cardiovascular disease and patients with underlying thromboembolic disease, which is very relevant for the Medicare population, are patients at very high risk” for blood clot issues that could result in stroke, Spyropoulos says.
If you have clotting issues, the best thing you can do as the coronavirus continues to spread is take your blood thinner medication as prescribed, Spyropoulos emphasizes. And if you experience symptoms of a blood clot (pain, redness, swelling) or a stroke (confusion, dizziness, numbness), “take them extremely seriously and go right to the emergency department,” Spyropoulos adds. The same goes for chest pain and difficulty breathing, which could indicate a clot in the lungs — yet another complication experts are seeing in COVID-19 patients.
Learning more about the long-term impacts
It's unclear whether COVID-19's impact on the nervous system has any long-term effects on brain health, but it's something researchers hope to better understand. Some complications seem to be “more transient” than others, such as loss of smell, Northwestern's Koralnik says. Other neurological events, including stroke, can leave more permanent damage.
Chou is overseeing a study that aims to capture “a more complete picture of exactly what is happening” between the virus and the nervous systems in patients hospitalized with COVID-19. Later phases of the research will follow patients who have recovered from the illness to learn more about any lasting neurological issues.
As new information surfaces about the various ways the new coronavirus affects humans, Chou says it's important not to panic. Most people who present symptoms of COVID-19 have the “classic symptoms,” including fever, cough and shortness of breath. “A much smaller portion of patients are reporting maybe something is wrong with their nervous system,” Chou adds — and experts still have so much more to learn as to why this is the case.
"Just like in a war, we need weapons and we need to gather intel. And science is our weapon in this disease,” Chou says.