This Is What the Coronavirus Can Do to Your Brain

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 of COVID-19

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.