COVID-19 could cause long-term loss of brain tissue, according to a study that examined brain imaging before and after a coronavirus infection.
University of Oxford researchers posted findings Tuesday to medRxiv, drawing on data from the U.K. Biobank study. The study has yet to be peer reviewed.
Brain scans taken before the coronavirus pandemic were compared to scans taken about 3 years later. Included were 394 COVID-19 patients and 388 healthy volunteers.
Among the patients, 15 were hospitalized and the rest only had mild-to-moderate symptoms, or no symptoms at all.
"Our findings thus consistently relate to loss of grey matter in limbic cortical areas directly linked to the primary olfactory and gustatory system," or areas in the brain related to the perception of smell and taste, authors wrote.
Dr. Scott Gottlieb, who serves on the board of COVID vaccine-maker Pfizer, told CNBC the destruction of brain tissue could explain why patients lost their sense of smell.
"The diminishment in the amount of cortical tissue happened to be in regions of the brain that are close to the places that are responsible for smell," Gottlieb said. "What it suggests is that, the smell, the loss of smell, is just an effect of a more primary process that’s underway, and that process is actually shrinking of cortical tissue."
The authors said the set of scans taken before the pandemic strengthens the findings because they help differentiate the effects of COVID-19 disease from patients’ pre-existing health conditions.
The three cerebral areas reveal a "significant loss" in thickness and volume of grey matter among COVID-19 patients, according to the authors, where the "parahippocampal gyrus, the lateral orbitofrontal cortex, and the superior insula" lie.
The "strongest deleterious effects of COVID-19 could be seen predominantly in the left hemisphere," they added.
Comparisons of the hospitalized patients "were not significant," but authors noted "comparatively similar" findings to the larger group of coronavirus patients with "a greater loss of grey matter in the cingulate cortex, central nucleus of the amygdala and hippocampal cornu ammonis."
Researchers said there was "a high number of mild cases," and added "there is a fundamental need for more information on the cerebral effects of the disease even in its mildest from."
Although expressing confidence in the study's results, researchers stopped short of connecting coronavirus to the loss of brain tissue.
That was due partly to the study lacking a breakdown of patients by factors such as oxygen saturation, and other limitations involved a "small number of participants from Asian, Black or other ethnic backgrounds other than White."
The authors also said there were issues in attaining data from test kits with varied accuracy.
"By using automated, objective and quantitative methods, we were able to uncover a consistent spatial pattern of loss of grey matter in limbic brain regions forming an olfactory and gustatory network,” the authors wrote.
"Whether these abnormal changes are the hallmark of the spread of the disease (or the virus itself) in the brain, which may prefigure a future vulnerability of the limbic system, including memory, for these patients, remains to be investigated," the authors said.
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