Following COVID-19, people often experience lingering cognitive symptoms of impaired attention, concentration, information processing speed, and memory, collectively known as brain fog. Researchers now say this common long COVID symptom is very similar to a condition called cancer therapy-related cognitive impairment (CRCI), or “chemo brain,” which is what happens in the brains of cancer survivors who have undergone chemotherapy treatment.

What the Researchers Did

CRCI involves inflammation in the brain, particularly in overactive immune cells called microglia, which disrupts normal processes in the hippocampus (important in memory) and in specialized cells called oligodendrocytes that have been linked to psychological disorders, like depression.

In a study posted January 10, 2022 on BioRxiv, a preprint platform for biological research, a team of American university, hospital, and government researchers tested their hypothesis that the same underlying processes in CRCI are also responsible for long COVID brain fog, even after a mild SARS-CoV-2 infection.

• The team looked at the brains of mice which had induced mild SARS-CoV-2 infections.
• The results were compared to brain tissue from nine people who had died from COVID-19. (The coronavirus had not infiltrated the brain tissue of either the mice or deceased humans.)
• They then assessed 63 long COVID patients: 48 experiencing brain fog (16 men and 32 women, average age 46.1 years) versus 15 without brain fog (four men and 11 women, average age 46.7 years).

What They Found

In both mice with mild SARS-CoV-2 infection and nine people who had died from COVID-19, scientists found evidence of brain inflammation similar to that seen in CRCI, with elevated levels of inflammatory proteins, including one called CCL11 which has been linked to abnormal nervous system development and cognitive dysfunction. 

CCL11 levels in mice remained high for at least seven weeks after viral infection, with impaired hippocampal function, decreased oligodendrocytes, and loss of protective nerve coating in the white matter below the brain cortex that is essential to normal brain function.

Out of the 63 long COVID patients examined, the researchers found elevated CCL11 plasma levels in the 48 people who experienced brain fog, but not in the remaining 15 people who were not experiencing brain fog.

What It Means

In all, the researchers said their findings “illustrate striking similarities between neuropathophysiology after cancer therapy and after SARS-CoV-2 infection, and elucidate cellular deficits that may contribute to lasting neurological symptoms following even mild SARS-CoV-2 infection.”

They speculate that CRCI treatments may be useful for long COVID-related brain fog, but the treatments would first have to be studied in this context.

The January study has yet to be peer reviewed, and needs further research to confirm results.

*Lapid, N. (2022, January 12). Long COVID brain fog found similar to ‘chemo brain’; clip-on device shows promise in virus detection. Reuters. https://www.reuters.com/business/healthcare-pharmaceuticals/long-covid-brain-fog-found-similar-chemo-brain-clip-on-device-shows-promise-2022-01-12