A large new study shows that covid-19 can cause brain damage in people who have not been exposed to the virus.
The study, published Monday in the journal Nature, is believed to be the first involving people who underwent brain scans before they contracted Covid. Neurological experts who were not involved in the research said it was valuable and unique, but they cautioned that the implications of the changes were unclear and did not suggest that people might have lasting damage or that the changes might profoundly affect thinking, memory or other functions.
The brains of people aged 51 to 81 were found to have some damage due to the sense of smell.
The chief of neurological infections and global neurology at the Yale School of Medicine, who was not involved, said that it was pretty convincing evidence that something changed in the brains of the group.
She cautioned that it was a stretch to make a conclusion that this has long-term implications for patients. We don't want the public to think that this is proof that everyone will have brain damage and not be able to function.
The UK Biobank is a repository of medical and other data from half a million people in Britain. Three years apart, the participants underwent two brain scans and some cognitive testing. Between the two scans, 401 people were positive for the coronaviruses, all of them between March 2020 and April 2021.
The other 384 participants formed a control group because they had not been exposed to the coronaviruses and had similar characteristics to the patients in areas like age, sex, medical history and socio-economic status.
People lose a small amount of gray matter with normal aging. The researchers said that the typical annual loss is between 0.2 percent and 0.3 percent.
Patients in the study who had their second brain scans within four and a half months after their first one lost more gray matter than did non patients. They lost more brain volume and showed more tissue damage.
I find it surprising that more was lost and that it is a generalized effect. I wouldn't have expected that much change.
The effects may be notable because the study involved mostly people who were not sick enough to need hospitalization after their initial Covid infections.
The number of hospitalized patients in the study was too small to yield conclusive data, but the results suggested that.
People who had Covid showed a greater decline on a cognitive test related to attention and efficiency in performing a complex task. The study is limited in what it can say about whether the gray matter loss and tissue damage the Covid patients experienced affected their cognitive skills.
None of them got thorough enough cognitive testing to know if they had significant deficits in these areas.
Some of the largest gray matter loss was in areas related to smell, but those areas are also involved in memory and other functions. The memory tests the Covid patients took were basic and brief.
The trail-making test is a type of exercise that involves alternating letters and numbers. Thevid patients took longer to complete the task, which might suggest weaknesses in focus, processing speed and other skills.
The diminished ability was related to the loss of gray matter in the cerebellum. The study doesn't prove cause and effect and the cerebellum isn't the first brain structure to explain changes.
The study didn't have information about people's symptoms, including whether they lost their sense of smell. It's unclear if the findings relate to the long-term condition, as the researchers couldn't identify whether any patients had long Covid.
The differences between people who are infectious and those who are not increased with age. I don't know if that's because younger people are better at trail-making than older people.
Dr. Michael warned that the findings could not be applied to younger people who are experiencing cognitive issues. We don't know if gray matter and tissue damage gets better with recovery, since it was only measured at one time point.
The range of brain areas where Covid patients experience more gray matter loss raised intriguing questions.
There is no one part of the brain that does everything.
The cause of the brain changes is not known. Inflammation and sensory deprivation have been found in other studies, as well as from disrupted sense of smell.
The chief of the section on infections of the nervous system at the National Institute of Neurological Disorders and Stroke, who was not involved in the study, asked if the brain changes could make Covid patients.
The researchers did not find the same brain changes in patients with non- Covid pneumonia.
The greatest value may be the indication that something has happened in the brain of these people.
She and others said that other scientists can build on these findings.
They have done a good job, now we need to do the studies to look at cognitive and psychiatric symptoms.
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