Covid can cause brain changes, new study finds
A large new study finds that COVID-19 may 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.
The study, published on Monday in the journal Nature, is believed to be the first to include people who had brain scans before and months after contracting Covid. Neurological experts not involved in the research said it was valuable and unique, but cautioned that the implications of the changes were unclear and may not necessarily cause permanent harm to people or that the changes could profoundly affect thinking, memory or others. can affect. Work.
The study, which included people aged 51 to 81, found shrinkage and tissue damage in brain regions primarily related to the sense of smell; Some of those regions are also involved in other brain functions, the researchers said.
“To me, this is very solid evidence that there is some change in the brains of this overall group of people with COVID,” said Dr. Serena Spudich, chief of neurological infections and global neurology at Yale School of Medicine. Study.
But, she cautioned: “To conclude that it has some long-term clinical implications for patients, I think it’s a stretch. We don’t want to scare the public and they have to think, ‘ Oh, this is proof that everyone is going to be out of mind and won’t be able to function.”
The study involved 785 participants in the UK Biobank, a repository of medical and other data on nearly half a million people in the UK. The participants each took two brain scans about three years apart, as well as some basic cognitive tests. Between its two scans, 401 participants tested positive for the coronavirus, all infected between March 2020 and April 2021.
Another 384 participants formed a control group as they were not infected with the coronavirus and had similar characteristics in areas such as age, gender, medical history and socioeconomic status of the infected patients.
With normal aging, people lose a small fraction of gray matter each year. For example, in areas related to memory, the typical annual impairment is between 0.2 percent and 0.3 percent, the researchers said.
But the Covid patients in the study – who had their second brain scan four and a half months after their infection – lost more than the non-infected participants, 0.2 percent and 2 percent of additional gray matter loss in different brain regions over three years. experienced. between scans. They also lost more overall brain volume and showed more tissue damage in some areas.
“I find it amazing how much is lost and how generalized it is,” said Dr. Spudich, who studies the neurological effects of Covid. She continued, “I would not have expected to see such a percentage change.”
The effects may be particularly notable because the study mostly included people who – like most COVID patients in the general population – were mildly affected by their initial COVID infection, ill enough to require hospitalization. Didn’t happen
The study’s lead author, Gwynelle Doud, 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, was too small to yield conclusive data, the results suggested that Their brain atrophy was worse than that of the mildly afflicted patients.
People who had COVID also showed a greater decline than uninfected people on cognitive tests related to attention and efficiency in performing a complex task. But outside experts and Dr. Doud noted that cognitive testing was rudimentary, so the study is very limited about what it can say about whether gray matter loss and tissue damage in COVID patients affected their cognitive skills. Is.
“None of them have done enough cognitive testing to know whether there were significant deficits in the many areas where they found these changes in volume,” said Dr Benedict Michael, an associate professor of neurological infections at the University of Liverpool. The neuropsychiatric effects of COVID were not included in the study. “We don’t know if this really means anything to the patient’s quality of life or function.”
For example, although some of the greatest gray matter loss was in areas related to odor, including the orbitofrontal cortex and parahippocampal gyrus, those areas are also involved in memory and other functions. But Covid patients did not perform worse than non-infected participants on memory tests, Dr. Dowd, however, said the memory tests he took were brief and basic.
The main cognitive assessment where COVID patients showed a decrease was the trail-making test, a connect-the-dots type of exercise involving alternating letters and numbers. COVID patients took longer to complete tasks, which may suggest weaknesses in focus, processing speed and other skills.
Dr. Doud said this reduced ability is related to loss of gray matter in a specific area of the brain’s cerebellum. But the study doesn’t prove cause and effect, Dr. said Spudich, who also noted that the cerebellum, which is primarily associated with balance, coordination and movement, “isn’t the first structure in the brain you think of” testing the scar-making ability to explain changes. .
An important limitation to the study, Dr. The reason, Doud said, is that researchers weren’t aware of people’s symptoms, including whether they had lost their sense of smell. The researchers also could not identify whether a patient had covid for a long time, so it is not clear whether the findings are related to that long-term condition.
The difference between infected and uninfected people increased with age. For example, in the trail-making test, performance was similar in both groups for people in their 50s and early 60s, but the difference widened significantly after that. “I don’t know if it’s because young people recover faster or they’re not as affected as they were initially,” Dr. Doud said. “It could be either or it could be both.”
Dr. Michael cautioned that the findings cannot be extrapolated to many young people who experience post-Covid brain fog and other cognitive issues. And since gray matter and tissue damage were only measured at one time-point after infection, “we don’t know if this is just a transient change that gets better with recovery,” he said.
External experts and the study’s authors said the extent of brain regions where Covid patients experience greater gray matter loss raised intriguing questions.
“There is no one part of the brain that does one thing,” Dr. Doud said. “Infected participants have parts of the brain with additional gray matter loss that have nothing to do with smell, and those that are related to smell are also involved in other brain functions.”
The cause of brain changes is not clear. The authors cited theories including inflammation, evidence of which has been found in other studies, and “sensory deprivation” from a disrupted sense of smell.
Dr Avindra Nath, head of the section on nervous system infections at the National Institute of Neurological Disorders and Stroke, who was not involved in the study, said another “important question” was whether brain changes could make COVID patients more prone. For future dementia or other deficits.
And while the researchers didn’t find similar brain changes in patients with non-Covid pneumonia, Dr Nath recommends studying patients with other coronaviruses or the flu “to see if these findings differ for COVID-19 or more.” are normal.”
Dr Spudich said the study’s greatest value may be its indication that “something has happened in the brain in these people,” adding that “I think people have realized that it’s so vague, it’s hard to measure.” “
Other scientists can now build on these findings, she and others said.
“It’s an important study, they did a good job,” said Dr. Michael, “now we need to do studies to look at the cognition and the psychological symptoms and the behavioral stuff and the neurological stuff and figure out what that means.” for the patient.”
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