Patients with COVID-19 brain fog experience the same type of excessive inflammation and damage to nerves in the brain as patients with “chemo brain,” a new study by scientists from Stanford University and Yale University has found.
The study, published June 12 in the journal Cell, found that the same brain cells and processes were affected by the damage. Lead authors include Dr. Michelle Monje, Professor of Neurology and Neurological Sciences at Stanford University and Akiko Iwasaki, Professor of Immunology and Molecular, Cellular and Developmental Biology at Yale University.
The experiment, which involved analysis of live mice and postmortem human brain tissue, found that those infected with SARS-CoV-2, the virus that causes COVID-19, experienced significant inflammation of a protein called cytokines in the cerebrospinal fluid exhibited. Within the brain, cytokines serve to send a signal to immune system cells to increase or decrease activity.
When these cytokines become inflamed and cause cells to overreact, microglia — cells that consume cellular debris in the brain — inflict increased damage to myelin, a layer of fat that protects the neuron’s axon, or arm. In both COVID-19 patients and people with chemo brains, the breakdown of myelin slows the transmission of nerve signals, the researchers found.
Monje and her colleagues found in previous studies that chemotherapy, like COVID-19 infection, affects the function of the brain’s white matter, regions of the brain normally rich in well-insulated nerve fibers that send signals quickly from one place transferred to the other.
Chemo brain refers to people who have received chemotherapy and report that they cannot remember certain information and have trouble completing tasks, concentrating, or learning new skills, according to the American Cancer Society.
Similarly, COVID-19 patients describe problems with concentration, memory function, and attention. In a study published by Stanford Medicine a year after the pandemic, scientists concluded that “about one in four COVID-19 patients had cognitive symptoms that lasted at least two months, even after mild infections.”
Symptoms of long COVID or post-COVID-19 states, as defined by the Centers for Disease Control and Prevention, include difficulty thinking or concentrating, also known as “brain fog.”
In addition to its connection to the chemo brain, the effects of COVID-19 brain fog are also comparable to other neurological conditions.
“The genes expressed in microglia after COVID-19 closely overlapped those expressed by microglia in other disease contexts, including cognitive decline in aging and in neurological disorders such as Alzheimer’s disease,” Stanford said in a press release Research.
In this latest experiment, the researchers found that “even mild COVID can cause marked inflammation in the brain that dysregulates brain cells and is expected to contribute to cognitive impairment,” they said.
With this newly discovered link between diseases and already existing chemo-brain research, Monje hopes to use this knowledge to inform treatments for COVID-19 brain fog. Monje’s team is already researching drugs that might relieve brain fog after chemotherapy, and they want to investigate whether these drugs are helpful after SARS-CoV-2 infection, Stanford’s press release said.
“The exciting message is that because the pathophysiology is so similar, the last few decades of research related to cancer therapy may lead us to treatments that can help the COVID brain fog,” Monje said.
Anthony Fernandez-Castañeda, postdoctoral fellow at Stanford University; Anna Geraghty, associate professor of neurology at Stanford; Peiwen Lu, postdoctoral fellow at Yale University; and Yale graduate student Eric Song are the lead authors of the study.