Covid can cause brain changes, new study finds

Covid-19 can lead to greater loss of gray matter and tissue damage in the brain than occurs naturally in people who have not been infect...


Covid-19 can lead to greater loss of gray matter and tissue damage in the brain than occurs naturally in people who have not been infected with the virus, a large new study find.

The study, published Monday in the journal Nature, is believed to be the first involving people who underwent brain scans both before contracting Covid and months after. Neurology experts who were not involved in the research said it was valuable and unique, but warned the implications of the changes were unclear and did not necessarily suggest people could have lasting harm or that the changes could profoundly affect thinking, memory, or other functions.

The study, involving people aged 51 to 81, found shrinkage and tissue damage primarily in areas of the brain related to smell; some of these areas are also involved in other brain functions, the researchers said.

“To me, this is pretty compelling evidence that something is changing in the brains of this global group of people with Covid,” said Dr. Serena Spudich, chief of neurological infections and global neurology at the Yale School of Medicine, who was not involved in the study.

But, she cautioned: ‘To conclude that this has long-term clinical implications for patients, I think is overstated. We don’t want to scare the public into thinking, “Oh, this is proof that everyone is going to have brain damage and not be able to function.”

The study involved 785 participants at UK Biobank, a repository of medical and other data from around half a million people in Britain. The participants each underwent two brain scans about three years apart, along with baseline cognitive tests. Between their two scans, 401 participants tested positive for the coronavirus, all infected between March 2020 and April 2021.

The other 384 participants formed a control group because they had not been infected with the coronavirus and had similar characteristics to infected patients in areas such as age, gender, medical history and socioeconomic status.

With normal aging, people lose a tiny fraction of gray matter each year. For example, in memory-related regions, the typical annual loss is between 0.2% and 0.3%, the researchers said.

But the Covid patients in the study – who had their second brain scan an average of four and a half months after their infection – lost more than the uninfected participants, experiencing between 0.2% and 2% more gray matter loss. in different regions of the brain during the three years between scans. They also lost more overall brain volume and showed more tissue damage in certain areas.

“I find it surprising in the sense of how much more has been lost and how widespread it is,” said Dr Spudich, who has studied the neurological effects of Covid. She added: “I didn’t expect to see so much percentage change.”

The effects may be particularly notable because the study mainly involved people who – like the majority of Covid patients in the general population – were mildly affected by their initial Covid infection, not getting sick enough to require hospitalization.

The study’s lead author, GwenaĆ«lle Douaud, a professor in the department of clinical neuroscience at the University of Oxford, said that although the number of hospitalized patients in the study, 15, is too small to provide data conclusive, the results suggest that their brains are atrophying. was worse than mildly affected patients.

People with Covid also showed a greater decline than uninfected people on a cognitive test related to attention and efficiency in performing a complex task. But outside experts and Dr Douaud noted that the cognitive tests were rudimentary, so the study is very limited in what it can say about whether the loss of gray matter and tissue damage experienced by Covid patients have affected their cognitive abilities.

“None of them underwent sufficiently extensive cognitive testing to know whether they had significant deficits in those many areas where they saw these volume changes,” said Dr. Benedict Michael, associate professor of infections. neurology at the University of Liverpool, which is doing research. the neuropsychiatric effects of Covid and did not participate in the study. “We don’t know if this actually means anything for the patient’s quality of life or function.”

For example, although some of the greatest loss of gray matter is in areas related to smell, including the orbitofrontal cortex and the parahippocampal gyrus, these areas are also involved in memory and other functions. But Covid patients did not perform worse than uninfected participants on memory tests, Dr Douaud said, although she added that the memory tests they took were brief and basic. .

The main cognitive assessment where Covid patients showed a deficit was the trail test, a type of dot-connecting exercise involving alternating letters and numbers. Covid patients took longer to complete the task, which could suggest weaknesses in concentration, processing speed and other skills.

Dr. Douaud said this reduced capacity correlated with the loss of gray matter in a specific cerebellum region of the brain. But the study doesn’t prove cause and effect, said Dr Spudich, who also said the cerebellum, primarily associated with balance, coordination and movement, “is not the primary structure you’re thinking about” to explain the ability changes on the trail-making trial.

A significant limitation of the study, Dr. Douaud said, is that the researchers did not have information about people’s symptoms, including whether they had lost their sense of smell. The researchers also couldn’t identify whether any patients had long-term Covid, so it’s unclear whether the findings relate to this long-term condition.

The differences between infected and uninfected people increased with age. In the trail-making test, for example, performance was similar in both groups for people in their 50s and early 60s, but the gap widened significantly afterward. “I don’t know if it’s because young people recover faster or they weren’t as affected initially,” Dr Douaud said. “Maybe one or the other or both.”

Dr Michael warned that the results could not be extrapolated to the many younger people with post-Covid brain fog and other cognitive problems. And since gray matter and tissue damage were only measured at some point after infection, “we don’t know if this is just a transient change that improves with recovery.” , did he declare.

Outside experts and the study authors said the range of brain areas where Covid patients experience more gray matter loss raises intriguing questions.

“There’s not one part of the brain that does one thing,” Dr. Douaud said. “There are parts of the brain in infected participants with additional gray matter loss that have nothing to do with smell, and those related to smell are also involved in other brain functions. “

The cause of the brain changes is unclear. The authors discussed theories such as inflammation, evidence of which has been found in other studiesand “sensory deprivation” due to a disturbed sense of smell.

Dr Avindra Nath, head of the nervous system infections section at the National Institute of Neurological Disorders and Stroke, who was not involved in the study, said another “critical question” was whether brain changes might make Covid patients more prone to dementia or other deficits in the future.

And although the researchers did not find the same brain changes in patients with non-Covid pneumonia, Dr. Nath recommended studying patients with other coronaviruses or influenza “to see if these findings are distinct. for Covid-19 or more generalizable”.

Dr Spudich said the study’s greatest value might be its indication that “something happened in the brains of these people”, adding that “I think people felt it was so vague, so difficult to measure”.

Other scientists can now build on these findings, she said, along with others.

‘It’s an important study, they’ve done a good job,’ said Dr Michael, adding: ‘Now we need to do studies to look at cognitive and psychiatric symptoms, behavioral and neurological elements and find out what it is means for patients.”

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Newsrust - US Top News: Covid can cause brain changes, new study finds
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