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When Aluko Hope, a critical care specialist at Montefiore Hospital in New York City, first meets patients in the Covid-19 recovery clinic, he spends a lot of time listening. “I don’t pretend to know what is what,” he says. Many aspects of Covid-19 are still unknown, including what a standard recovery looks like. So Hope has to pay attention to what survivors describe and try and tease out which of their body’s systems are still recuperating.
The most common complaints Hope hears are fatigue, shortness of breath, and coughing. But survivors also describe sadness and depression. Hope says many carry a double burden: gratefulness for having survived, and grief over the trauma of being hospitalized and separated from family. And then there are memory problems. About a third of his patients say they can’t recall telephone numbers they used to know, or that they struggle to remember the right word, feeling like it’s on the tip of their tongue but just out of reach. They can’t remember where their keys are, what basic traffic rules are.
This mental fuzziness, often referred to as “brain fog,” has become one of a number of reported Covid-19 recovery symptoms. And while patients are often alarmed and frustrated that they can’t resume their normal lives, doctors say it isn’t particularly surprising. “We’ve encountered brain fog and mental fatigue commonly post-infection. We do have experience with this,” says Marie Grill, a neurologist at the Mayo Clinic who says it often follows other infections like Lyme disease, Epstein-Barr (better known as “mono”), and other types of herpes viruses. “A lot of us are not surprised at all to be encountering this, because we have seen it so many times,” she says.
But while doctors may have been expecting brain fog, there are still plenty of questions about what causes the symptom, who it affects the most, and how to treat it. “We don’t have the whole story,” says Adam Kaplin, a neuropsychiatrist at Johns Hopkins University. “What we don’t know is probably much larger than what we do know.”
What we know is that patients describe a very similar set of symptoms. They say their brains work more slowly. They can’t pick up information in conversation as easily as they used to, and they struggle with short-term memory: They’ll walk to the kitchen, for instance, and forget what they were looking for. Multitasking is impossible. It takes them longer to get things done, and they often feel confused and overwhelmed. Some patients struggle to return to work or to school.
Brain fog might sound alarming, but it’s actually not unusual for people who have recently been hospitalized or intubated. “Just being in the ICU [intensive care unit] has effects on the brain,” says Kaplin. One 2012 study published in the Annals of Intensive Medicine found that between 30 and 80 percent of patients experience delirium, which can lead to cognitive decline, during their stay in the ICU. Another study published in 2013 in The New England Journal of Medicine found that three months after leaving the ICU, 66 percent of patients were still experiencing some level of cognitive impairment.
There are a number of reasons why the brain might be so affected by a serious illness. First, Kaplin says, the brain is highly dependent on, and sensitive to, other systems in the body because it doesn’t have any fat stores of its own. Instead, the brain needs the heart and lungs to pump a steady stream of oxygenated, glucose-rich blood to fuel it. If the lungs or the heart aren’t working properly, that will affect what’s happening in the brain too. So if a patient is experiencing common Covid-19 symptoms like shortness of breath, blood clots, or having heart problems, which have also been linked to the novel coronavirus, then there’s a possibility that their brain isn’t working the way it normally does.
Then there’s the cocktail of heavy drugs that doctors often use to keep patients who are on ventilators in the ICU sedated. “These drugs have effects on people's brains,” says Kaplin, who adds that almost all the patients he sees at the Covid-19 clinic who were ventilated describe having vivid hallucinations while in the hospital.
But some clinicians say that not all of the patients complaining of brain fog were ventilated or in the ICU. Some were never even sick enough to go to the hospital. “We’re seeing this in all sorts of people,” says Joanna Hellmuth, a neurologist at the UC San Francisco Memory and Aging Center. She says many of her patients had relatively mild infections, but nevertheless have lingering cognitive problems that make it hard to go back to work or to school. And they don’t all fit neatly into one demographic.“It’s not just old people who are getting these cognitive symptoms,” she says. “We don’t know who is at risk, or why.”
It could be that the SARS-CoV-2 virus itself is damaging neurons, says Hellmuth. Or it could be that when the body mounts an immune response to the virus, that inflammation also harms how the brain operates. “Something about that activation of the immune system is potentially causing worse cognitive function,” she says. “It might be that prolonged immune activation after Covid that is creating these cognitive changes.”
There are other documented neurological effects related to Covid-19, although scientists don’t yet understand how the virus—or inflammation reacting to it—affects the central nervous system. Patients have reported a wide variety of other symptoms, including tingling, seizures, dizziness, and confusion. One of the most common, loss of smell and taste, could indicate that the virus is affecting olfactory neurons or even the olfactory bulb, where the brain processes scent. Unlike the anosmia that accompanies the common cold, Covid-19 patients often lose their sense of smell immediately, and even though they are not congested—a sign that the problem isn’t as simple as too much mucus.
Another possible explanation could be that as survivors recover, they may still be exhausted from fighting off the infection or have anxiety, depression, or post-traumatic stress disorder—all of which are common in patients recuperating from an ICU stay, and all of which can affect brain function. When someone is experiencing emotional stress, the body releases the hormone cortisol, which inhibits normal activity in the hippocampus, the area of the brain where new memories are created. That could be why people with depression often struggle to focus, and why untreated depression or PTSD may lead to higher rates of Alzheimer’s disease and dementia later in life.
Scientists don’t know how long these cognitive changes will last in Covid-19 patients, nor if they will have a lasting effect on brain function, though Hellmuth is starting a study that will use brain scans, spinal taps, and cognitive tests to track Covid-19 brain fog patients over time. She says it’s important that patients and the public understand that these cognitive changes aren’t a personal failing; they are part of a medical condition. “I think ‘brain fog’ is a colloquial term, and it doesn’t medicalize it in the way that gives people the validation that it’s a real issue,” she says.
While researchers study what else might be unique about Covid-19-related memory problems, clinicians are borrowing techniques for treating other cognitive issues like stroke or traumatic brain injury. Hellmuth recommends that people eat a healthy Mediterranean diet, get plenty of sleep, and find some kind of brain-engaging activity they enjoy, like doing crossword puzzles or taking a class online. “Cardiovascular exercise is probably the big-ticket item,” she says—walking, jogging, Zumba, anything to get the heart pumping and the body moving.
At the clinic in New York, Aluko Hope also checks other health indicators that aren’t specific to Covid-19 but create similar symptoms. He first tries to address any extra issues like trouble sleeping, blood pressure problems, medications, or thyroid issues that could be causing cognitive effects. “A lot of patients improve just by treating these other contributory factors,” he says.
But the conditions surrounding Covid-19 could also make recovery more difficult for people suffering from brain fog. “Something that is unique to Covid is the pandemic itself,” says Ann Parker, a critical care specialist at Johns Hopkins University. “Our patients who are in the hospital, and even patients in the community who aren’t hospitalized, generally have a lot less access to loved ones than they would outside the pandemic.” Social interactions often help patients start to rehab their brains. Visits with family and friends can keep them engaged and help them flex the cognitive powers that lost strength during an illness. But now many people are alone, afraid to be near others—some are even shunned by family or friends who are scared they’re still infectious. That fear and anxiety, along with the sense of isolation, could make it harder for people to recover and drive other complicating factors like depression.
Above all, doctors say, people need to be patient and have realistic expectations about how long it will take to feel normal again after being released from the hospital. “People come out and they’re like, ‘I’m here, I’m back.’ They don’t understand why they’re irritable, why they’re not themselves,” says Kaplin. He tries to help patients set reasonable goals for their progress and not to get angry when recovery isn’t as fast or as smooth as they expect. “You’ve really got to go easy on yourself,” he says. “Stop being your worst critic.”