The study found excessive inflammation caused by COVID-19 and cognitive impairment that can occur after chemotherapy, sometimes referred to as “chemobrain,” both damage the same brain cells and processes. The findings were published Tuesday in the peer-reviewed journal Cell. The research studied mice mildly infected with SARS-CoV-2, the virus that causes COVID-19, and postmortem human brain tissue collected early during the pandemic. The researchers found that even mild COVID-19 can create enough inflammation to cause cognitive impairment. “I think we’re really just starting to understand this,” Dr. Michelle Monze, a neuro-oncologist and professor at Stanford, told CTV’s “Your Morning” on Wednesday. “People infected with COVID early in the pandemic showed a pretty shockingly high rate of cognitive impairment. Many studies have shown that up to one in four patients have some degree of lasting cognitive impairment, and so we’re trying to figure that out.” Inflammation is a defense mechanism the body uses to respond to injury or infection, such as when a person’s skin swells after a cut. Inflammation that lasts for a long time or occurs in healthy tissue, known as chronic inflammation, can be harmful. For many patients, COVID-19 can lead to cognitive symptoms such as problems with attention, concentration, memory and executive function that could potentially last two months or more after a mild infection, researchers say. Monje and her team have previously studied the effect of chemotherapy on cognitive decline. They say chemotherapy can damage the brain’s white matter, areas of insulated nerve fibers that transmit signals quickly with the help of a fatty coating called myelin. During “chemobrain,” damaged myelin can slow nerve signal transmission. COVID-19 also produces an immune response strong enough to create widespread inflammation, which Monje suspects may be causing the cognitive problems seen in long-term COVID-19. Even if the virus causes a mild infection that’s limited to the lungs, Monje says the inflammation can create a cascading effect that affects a person’s brain cells. The study authors report that the effect of newer subvariants of COVID-19, such as Omicron, as well as breakthrough infections in vaccinated individuals, remains to be fully determined. But they say emerging data show that the risk of cognitive decline may be lower in nascent infections in fully vaccinated people. The effects on the brain of a respiratory COVID-19 infection in children and the elderly also require more research, they said. But understanding this link between COVID brain fog and chemotherapy could provide “new therapeutic ideas and hopefully reverse this cognitive impairment,” says Monje. Her team is currently researching drugs that could relieve brain fog after chemotherapy, which she says could prove useful after a COVID-19 infection. “I think what’s really encouraging is that the cognitive decline that occurs after cancer treatment is now understood well enough that the principles of clinical trials exist,” he said. “In fact, some of this really promising work is being driven out of Toronto at SickKids[hospital]and I’m hoping that some of these insights from cognitive impairment related to cancer treatment will help us understand new pathways to do the cognitive decline that occurs after COVID better for patients.”
