Even mild cases of COVID-19 can lead to brain shrinkage and cognitive impairment

(ORDO NEWS) — Most of what we know about how COVID can affect the brain comes from research into severe infection. In people with severe COVID, inflammatory cells from outside the brain can invade brain tissue and spread inflammation.

There may be changes in the blood vessels. Brain cells may even have changes similar to those seen in people with Alzheimer’s disease.

For the first time, a new study looked at the effects of mild COVID (that is, an infection that did not result in hospitalization) on the brain. The findings may explain some of the brain changes that contribute to the long course of COVID.

Brain scans and tests show changes

Many COVID survivors report a feeling of “brain fog”, fatigue, and trouble concentrating and remembering long after the initial symptoms have subsided. These problems, collectively referred to as “prolonged COVID”, can continue for months even after a mild infection.

Long-term COVID is very common and can affect more than half of people who get COVID, even if they have a mild form of the disease.

The scientists collected the data as part of the massive UK Biobank database. They studied the results of brain magnetic resonance imaging (MRI) and brain function tests in 785 volunteers who were screened before the pandemic.

They then compared that data with the same data collected three years later, when about half of the participants had a mild form of COVID infection and the other half did not contract COVID. This allowed scientists to determine the specific effects of a mild form of COVID infection on the structure and function of the brain.

The group that contracted mild COVID an average of five months prior had thinning of brain tissue in several areas of the brain ranging from 0.2% to about 2% compared to pre-COVID scans.

This is equivalent to one to six years of normal brain aging. Areas of the brain affected included the parahippocampal gyrus (an area associated with memory) and the orbitofrontal cortex, which is located in the front of the brain and is important for smell and taste.

The treated group also saw a decrease in overall brain size between MRI scans, which was not seen in the untreated group, and there were altered connections between different brain regions in the olfactory cortex, an area associated with smell.

They performed worse on a test of attention and mental flexibility, which was associated with a decrease in the volume of the cerebellum region associated with smell and social relations.

Comparison with other diseases

To show that these changes are specific to COVID and not just associated with a respiratory illness, the scientists also tested a group of people who had had pneumonia. They did not see the same changes, confirming their connection to COVID.

Decreased brain volume is a feature of many brain diseases and degeneration-related disorders and has been found, in particular, in people with mild cognitive impairment, Alzheimer’s disease, depression, and traumatic brain injury.

Memory and attention problems are also common in people with these diseases and disorders, indicating that mild COVID infection may accelerate brain degeneration. These changes may explain symptoms of long-term COVID infection, such as brain fog.

The study did not look at the mechanisms by which mild COVID affects the brain. However, the authors speculate that this may be due to inflammation, degeneration spreading along brain pathways associated with smell, or sensory deprivation due to loss of smell.

Is it the same for everyone?

So does this study prove that all people who have had a mild COVID infection will have the same brain changes and long-term brain degeneration? Not necessary.

There are several important points that we still do not know. In particular, will these brain changes get worse over time, or will they return to normal or previous levels of functioning. More research over the long term will help us understand the trajectory of change in the brain.

This study also included people aged 51-81, so we do not know if these results apply to younger people or children.

The brain changes found in this study were more pronounced in older participants, so it may be that older people are more susceptible. More research is needed to determine if the same brain changes will occur in younger people, or if these results are specific to older people.

There were some differences between pre-COVID groups: smaller volumes of regions deep in the brain. However, they were in different areas of the brain than those that were affected after COVID.

The scientists also found slightly reduced scores in brain functions such as thinking and memory in the group that had COVID. This study did not exclude people with degenerative brain diseases such as Alzheimer’s or Parkinson’s, but the scientists do not think they could explain the changes found.

Effects of different options and vaccination unknown

Due to the nature of the study, information about the strain of COVID that people were infected with was not available. Therefore, we cannot assume that the results of the study will be the same for people with the currently more common Omicron strain.

We also cannot determine what effect vaccination might have on reducing changes in the brain. Given the timing of the study, it can be assumed that the majority of people in the post-vaccination group were infected in 2020 and may not have been vaccinated.

This study provides the first important information about changes in the brains of people with mild COVID infection. Until we have all the information, we should be alert but not alarmed by the results that are emerging. The Conversation

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