Brain fog after COVID-19 has similarities with ‘chemo brain’

Stanford scientists have found that “brain fog” – the condition that affects 20 to 30 percent of COVID-19 patients – is biologically similar to the persistent cognitive impairment suffered by cancer patients undergoing chemotherapy.

In both cases, excessive inflammation damages ”the same brain cells and processes”.

Certainly, recipients of COVID-19 and chemo struggle with the same symptoms: memory problems, a decreased ability to pay attention and concentrate, and slower information processing.

While COVID-19 brain fog and “chemo brain” don’t match biologically, the new research suggests enough overlap that treatments for both conditions could be reached earlier.

“The exciting message is that because the pathophysiology is so similar, the last few decades in cancer therapy-related research could lead us to treatments that could help COVID brain fog,” said Dr. Michelle Monje, professor of neurology and neurological sciences at Stanford.

In terms of recovery, COVID-19 and the “chemo brain” — as cancer doctors often call the condition — are mixed bags. Many patients with these conditions eventually recover their brain function, but others do not.

Insulation damage

Brain fog after COVID-19 has similarities with 'chemo brain'

During two decades of research, Dr. Monje and her colleagues found that chemotherapy impairs the brain’s white matter function, ”regions of the brain normally rich in well-insulated nerve fibers that quickly transmit signals from one place to another”.

Myelin, the fat layer that insulates the body from neurons, helps speed up the transmission of nerve signals. In the chemo brain, myelin is damaged, and transmission is slowed down.

“When the pandemic started, I started to worry that we would see similar neurological consequences from this deeply immunogenic virus,” said Dr. Monje.

These concerns were raised when it became clear that the coronavirus virus “triggered such a strong immune response, including widespread inflammation.”

animal testing

The first experiments examined mild cases of COVID-19 in mice.

An important finding was that the formation of new neurons in the hippocampus – a brain region involved in learning and memory – was impaired.

After infection, the mice also showed changes between cells in the white matter that help envelop the neurons in isolating myelin.

The cells that make myelin, called oligodendrocytes, were damaged by mild COVID-19.

The researchers also found a loss of myelin, which could be detected within a week and persisted for seven weeks after infection.

These findings were supported when the researchers examined brain tissue data collected from a small group of people who died suddenly in New York City in the spring of 2020.

The team of dr. Monje is researching drugs that can relieve brain fog after chemotherapy and plans to investigate whether these drugs are helpful after a SARS-CoV-2 infection.

“While there are many similarities with cognitive impairment after cancer, there are likely to be differences as well,” she said.

“We need to explicitly test potential therapies for COVID.”

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