Study: COVID may cause changes in brain

Hundreds of brain scans of people before and after they had COVID-19 — even mild cases — have revealed shrinkage and tissue damage in regions of the brain linked to smell and mental capacities, according to a British study published Monday.

Also on Monday, the global death toll from COVID-19 eclipsed 6 million, according to Johns Hopkins University.

The study, published in the journal Nature, was done at the University of Oxford. It is the first major study involving people who underwent brain scans both before they contracted the coronavirus and months after.

Assessing the brain itself through a series of MRI scans, the researchers found evidence of an average decline in the overall size of the brain following COVID. The scans showed signs of tissue damage in areas of the brain related to smell, as well as a reduction in gray matter in parts linked to smell and memory.

Previous studies have shown people with significant and repeated loss of smell also have an associated loss of gray matter. However, this study didn't evaluate whether patients actually experienced loss of smell.

Gwenaëlle Douaud, lead author of the study and an associate professor of neurosciences at the University of Oxford, told NBC News that the excess loss of brain volume she and her colleagues observed in the brain scans is equivalent to at least one extra year of normal aging.

"It is brain damage, but it is possible that it is reversible," she said. "But it is still relatively scary because it was in mildly infected people."

Douaud explained that it is normal for people to lose 0.2 percent to 0.3 percent of gray matter every year in the memory-related areas of the brain as they age, but in the study evaluation, patients who had been infected with the coronavirus lost an additional 0.2 percent to 2 percent of tissue compared with those who hadn't been infected.

Dr Richard Isaacson, a neurologist and director of the Florida Atlantic University Center for Brain Health who wasn't involved in the study, told CNN that the study's findings were noticeable for clinicians, but he added that the overall impact on individuals was difficult to determine and could be small.

Neurological experts not involved in the research told The New York Times that the implications of the changes were unclear and didn't necessarily suggest that people might have lasting damage or that the changes might profoundly affect thinking, memory or other functions.

The study also noted that the results were representative of an average and that not all patients who have had COVID-19 will display brain abnormalities.

The study also had some limitations, including the lack of information on how severe the individual cases of COVID-19 were, though researchers accounted for which cases resulted in hospitalization.

Researchers also were unable to identify specific strains of the coronavirus among the participants.

Researchers at Oxford analyzed data from brain scans and tests collected from participants both before they were infected with the disease and from a second round conducted later, close to five months on average after they tested positive.

That data was also compared to results from 384 similar people who had not gotten sick, as well as a handful of people who had pneumonia and influenza.

Compared with 384 uninfected control subjects, those who tested positive for COVID had greater overall brain shrinkage and more gray matter shrinkage, particularly in areas linked to smell.

Those who were infected also typically scored lower on a mental skills test than uninfected individuals, the study said. Lower scores were associated with a greater loss of brain tissue in the parts of the cerebellum involved in mental ability.

The effects were more pronounced in older people and those hospitalized as a result of the disease, but still evident in others whose infections were mild or asymptomatic, the research suggested.

Further scans are needed to determine whether the brain changes are permanent or partially reversible, the researchers said.

Last year, a survey published by the Centers for Disease Control and Prevention (CDC) found close to two-thirds of Americans who tested positive for the coronavirus reported at least one long-term symptom more than four months after being infected — 55.5 percent included "cognitive dysfunction", like difficulty concentrating or memory loss.

Separate research also published in Nature and done by researchers at the University of Edinburgh identified 16 new genetic variants associated with severe illness from COVID and named a number of existing drugs that could be repurposed to prevent patients from getting severely ill, some of which are already in clinical trials.

"These results explain why some people develop life-threatening Covid-19, while others get no symptoms at all. But more importantly, this gives us a deep understanding of the process of disease and is a big step forward in finding more effective treatments," said Dr Kenneth Baillie, a consultant in critical care medicine at the university who led the researchers.