Study links even mild Covid-19 to brain changes

The study, published Monday in the journal Nature, is considered the largest of its kind. He found that the brains of those who had Covid-19 had greater gray matter loss and abnormalities in brain tissue compared to those who did not have Covid-19. Many of these changes involved the region of the brain related to smell.

“We were quite surprised to see clear differences in the brain even with mild infection,” lead author Gwenaëlle Douaud, an associate professor of neuroscience at the University of Oxford, told CNN in an email.

Douaud and colleagues assessed brain imaging of 401 people with Covid-19 between March 2020 and April 2021, both before infection and an average of 4.5 months after infection. They compared the results with brain imaging of 384 uninfected people similar in age, socioeconomics and risk factors such as blood pressure and obesity. Of the 401 people infected, 15 patients had been hospitalized.

The 785 participants were aged between 51 and 81 and were all part of the UK Biobank, an ongoing government health database of 500,000 UK participants launched in 2012.

Douaud explained that it’s normal for people to lose 0.2% to 0.3% gray matter each year in areas of the brain related to memory as they age, but in assessing study, patients who had been infected with the coronavirus lost an additional 0.2% to 2% of tissue compared to those who had not been infected.

In addition to imagery, participants were also tested for executive and cognitive function using the Trail Making Test, a tool used to help detect dementia-associated cognitive impairment and test speed and function. processing of a person’s brain. The authors found that those with the greatest loss of brain tissue also had the worst results on this test.

While the areas of the brain most affected appear to be linked to the olfactory system, Douaud said it’s unclear why this is the case.

“Since the abnormal changes we see in the brains of infected participants could be partly related to their loss of sense of smell, it is possible that its recovery leads to these brain abnormalities becoming less marked over time. , it is likely that the harmful effects of the virus (whether direct or indirect via inflammatory or immune reactions) will diminish over time after infection.The best way to find out would be to re-scan these participants in one or more two years,” she said.

Douaud added that the researchers plan to reimage and test the participants in one to two years.

The greater impact of brain changes

And while the study finds some association between the infection and brain function, it’s still unclear why. Previous studies have shown that people with severe and repeated loss of smell also have an associated loss of gray matter. However, this study did not assess whether the patients actually experienced a loss of smell.

The authors cautioned that the findings were only one-off, but noted that they “raise the possibility that the longer-term consequences of SARS-CoV-2 infection may ultimately contribute to the disease of Alzheimer’s or other forms of dementia”.

Although the results were noticeable, they weren’t enough to cause alarm, said Dr. Richard Isaacson, neurologist and director of the Florida Atlantic University Center for Brain Health. Isaacson was not involved in the study.

Isaacson said the study results were noticeable to clinicians, but he added that the overall impact on individuals was difficult to determine and could be small. “It’s really hard to know the long-term clinical impact and the impact on quality of life in a situation like this,” he said.

“The brain can be affected by other mechanisms such as immune, inflammatory, vascular, or psychological/behavioral changes, but not by direct infection,” said Dr. Alan Carson, professor of neuropsychiatry at the Center for Clinical Brain Sciences at the University of Edinburgh, which was not involved in the study.

“What this study almost certainly shows is the impact, in terms of neural changes,” he said. “But I don’t think it helps us understand the mechanisms underlying cognitive change after Covid infection.”


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