Researchers are sifting through symptoms to figure out what the virus does to the brain. Scientists have been racing to understand how the mysterious new virus that causes COVID-19 damages not only our bodies, but also our brains.
Early in the pandemic, some infected people noticed a curious symptom: the loss of smell. Reports of other brain-related symptoms followed: headaches, confusion, hallucinations and delirium. Some infections were accompanied by depression, anxiety and sleep problems.
Recent studies suggest that leaky blood vessels and inflammation are somehow involved in these symptoms. But many basic questions remain unanswered about the virus, which has infected more than 145 million people worldwide. Researchers are still trying to figure out how many people experience these psychiatric or neurological problems, who is most at risk, and how long such symptoms might last. And details remain unclear about how the pandemic-causing virus, called SARS-CoV-2, exerts its effects.
Getting the numbers
For now, some scientists are focusing on the basics, including how many people experience these sorts of brain-related problems after COVID-19.
A recent study of electronic health records reported an alarming answer: In the six months after an infection, one in three people had experienced a psychiatric or neurological diagnosis. That result, published April 6 in Lancet Psychiatry, came from the health records of more than 236,000 COVID-19 survivors. Researchers counted diagnoses of 14 disorders, ranging from mental illnesses such as anxiety or depression to neurological events such as strokes or brain bleeds, in the six months after COVID-19 infection.
Mental health disorders are “extremely important things to address,” says Allison Navis, a neurologist at the post-COVID clinic at Icahn School of Medicine at Mount Sinai in New York City. “But they’re very different than a stroke or dementia,” she says.
About 1 in 50 people with COVID-19 had a stroke, Taquet and colleagues found. Among people with severe infections that came with delirium or other altered mental states, though, the incidence was much higher — 1 in 11 had strokes.
Fig:Serious neurological damage, such as these strokes caused by blocked blood vessels, turn up in people with COVID-19.
Blood vessels scrutinized
Early on in the pandemic, the loss of smell suggested that the virus might be able to attack nerve cells directly. Perhaps SARS-CoV-2 could breach the skull by climbing along the olfactory nerve, which carries smells from the nose directly to the brain, some researchers thought.
That frightening scenario doesn’t seem to happen much. Most studies so far have failed to turn up much virus in the brain, if any, says Avindra Nath, a neurologist who studies central nervous system infections at the National Institutes of Health in Bethesda, Md. Nath and his colleagues expected to see signs of the virus in brains of people with COVID-19 but didn’t find it. “I kept telling our folks, ‘Let’s go look again,’” Nath says.
That absence suggests that the virus is affecting the brain in other ways, possibly involving blood vessels. So Nath and his team scanned blood vessels in post-mortem brains of people who had been infected with the virus with an MRI machine so powerful that it’s not approved for clinical use in living people. “We were able to look at the blood vessels in a way that nobody could,” he says.
Inflamed body and brain
Inflammation in the body can cause trouble in the brain, too, says Maura Boldrini, a psychiatrist at Columbia University in New York. Inflammatory signals released after injury can change the way the brain makes and uses chemical signaling molecules, called neurotransmitters, that help nerve cells communicate. Key communication molecules such as serotonin, norepinephrine and dopamine can get scrambled when there’s lots of inflammation.
Neural messages can get interrupted in people who suffer traumatic brain injuries, for example; researchers have found a relationship between inflammation and mental illness in football players and others who experienced hits to the head.