Some coronavirus patients may suffer from 'micro-strokes' that are too small to notice. Dizziness or confusion could be a sign.

• A growing body of evidence suggests that coronavirus patients, including young people, could suffer from strokes as a result of blood clots.
• Dr. Nate Favini, who treats coronavirus patients in San Francisco, said he suspects that some patients may experience "micro-strokes" without realizing it.
• Some coronavirus patients experience neurological issues like dizziness, confusion, or feeling "off," but more data is needed to link these symptoms to the virus.
• Visit Business Insider's homepage for more stories.

New York City doctors detected an unusual pattern in April: A small group of young coronavirus patients experienced large-vessel strokes caused by blood clots that traveled to the brain.

Before the pandemic, doctors at Mount Sinai Hospital in New York City saw fewer than one patient under 50 with a large-vessel stroke over the course of two weeks, on average. But from March 23 and April 7, they saw five patients who fit that description. All tested positive for COVID-19.

"Our report shows a sevenfold increase in incidence of sudden stroke in young patients during the past two weeks," Thomas Oxley, a neurosurgeon at Mount Sinai, told CNN 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-19."

Doctors think the strokes are likely tied to coronavirus-related blood clots.

"The virus can create a propensity to clotting," Dr. Nate Favini, the medical lead at Forward, a primary-care practice that's collecting data on coronavirus patients around the country, told Business Insider. "My suspicion is that's what's behind the strokes that we're seeing in younger folks."

But not all strokes are life-threatening, he added.

"My suspicion is that there are some people who get essentially small, micro-strokes without even realizing it," Favini said. Those patients, he added, "may have some cognitive or even mood changes" that linger even after they're no longer infected. They also experience dizziness, confusion, or delirium.

'My mind is just not quick like it normally is'

Chinese researchers recently determined that the coronavirus can invade a person's nervous system: An April study of 214 patients in Wuhan, China, found that more than a third of patients had neurological symptoms. This was more common among people with severe infections. Less than 6% of the patients experienced a stroke.

Of the patients studied, 25% experienced dizziness, headache, confusion, delirium, seizure, or impaired balance or coordination. Among those symptoms, dizziness was the most common, affecting nearly 17% of patients.

"There's also people who describe not feeling right for a long time — just feeling 'off' in some way," Favini said.

A handful of doctors recently told Kaiser Health News that they've started to identify these neurological issues among older coronavirus patients in particular.

"They get weak and dehydrated, and when they stand to walk, they collapse and injure themselves badly," Dr. Sam Torbati, medical director of the emergency department at Cedars-Sinai Medical Center, told Kaiser. "When we test them, we discover that what's producing these changes is a central nervous system effect of coronavirus."

But the symptoms have shown up among young, otherwise healthy patients as well.

"I was really confused the whole first week I had symptoms and into the second week," Kelsey Meeks, a 36-year-old attorney who tested positive for the virus on April 5, told Business Insider. "My mind is just not quick like it normally is."

Meeks said she recently had to address an envelope and couldn't remember her own ZIP code.

"I wrote the envelope three times before I finally got it right," she said. "It's frustrating for your brain to not work the way it has your whole life."

A link between strokes, clots, and the coronavirus

Scientists still aren't sure why these neurological symptoms manifest. It may be that the virus damages neurons in the nose, which allows it to cross over from the respiratory tract to the brain. Scientists have also found evidence that the virus latches onto ACE2 receptors in the interior lining of blood vessels. From there, it might penetrate the barrier between the blood and the brain.

Doctors have also linked blood clots to the increased prevalence of strokes among coronavirus patients. A Dutch study of 184 coronavirus patients in the ICU found that nearly one-third of patients had blood clots. Around 4% of patients had blood clots blocking their arteries, which can cause a stroke.

One patient in New York City, a healthy 33-year-old woman, came to the hospital with impaired speech and numbness and weakness on the left side of her body. Doctors discovered she had a blood clot in her carotid artery, which supplies blood to the brain.

The reason for these clots among coronavirus patients is also somewhat of a mystery. The virus may attack blood vessels directly, but it could also damage those vessels by inducing a strong inflammatory response or depleting oxygen levels in the blood.

Favini said it takes a particular CT scan, in which dye gets injected into the blood vessels, to be able to see blood clots. That means clots could go undetected among patients who are being treated for mild coronavirus symptoms, like fever, cough, or sore throat.

For now, the evidence linking neurological symptoms to the coronavirus is tenuous. But Favini said strokes are a particularly dangerous threat.

"For some of these folks with strokes, that damage is permanent and they may not have full recovery," he said.