What is the impact of the coronavirus on the brain? | Image source: pixabay.com
Editor's Note
For patients recovering from COVID-19, whether there are sequelae and how much the sequelae have on health is always a class of concern. On March 8, the journal Nature published a study with a sample size of more than 400, which systematically analyzed the brain imaging data of patients with new crown pneumonia before and after being infected by the virus, which is of reference significance for understanding the impact of new crown virus on the central nervous system and whether it can be recovered in the long run.
Written by | Ji Yongsheng
Editor-in-charge | Chen Xiaoxue
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At present, the COVID-19 epidemic is still raging around the world.
After being infected by the new crown virus, the first symptoms of some patients are loss or loss of smell and taste. These changes in sensory function actually reflect changes in the structure or physiology of the central nervous system (brain). Brain imaging can clearly document this change, but changes in the central nervous system in patients with COVID-19 have been reported directly through medical imaging. Jonas A. Hosp, a professor at the University Medical Center freiburg in Germany, found that 10 patients had a decrease in metabolic levels in the frontal parietal lobe [1] after imaging the brains of 15 patients with new coronary pneumonia who were in the subacute phase and had abnormal sense of smell and taste [1].
Image source[1]
Figure 1 |
E Guedj's team from the Department of Nuclear Medicine at the University of Aix-Marseille in France also used PET methods to detect metabolic changes in the brains of two COVID-19 patients and found that metabolic levels were reduced in sites including olfactory/rectus gyrus, amygdala, hippocampus, and parahippocampus [2].
Image source[2]
Figure 2 |
The above two studies provide some information for us to understand the impact of COVID-19 infection on the central nervous system. However, the number of cases involved in both studies was small, and the researchers imaged the brains of infected patients, so it cannot be ruled out that these changes existed before the patients were infected with the new crown virus. Whether these physiological changes will increase the susceptibility of people to the new crown virus is also unknown.
To solve the above doubts, it is necessary to compare the imaging data of the brain of patients with new coronary pneumonia before and after being infected by the virus.
Following the above line of thinking, the team of Gwena lle Douaud of the Wellcome Centre for Integrative Neuroimaging, WIN of the University of Oxford in the United Kingdom systematically analyzed the brain imaging data of 401 patients with new crown pneumonia before and after being infected by the virus, and found that new crown virus infection can cause greater reduction in gray matter thickness and tissue contrast in the orbitofrontal cortex and parahipocampal retracement (related to smell and memory). Tissue damage is greater in areas of primary olfactory cortex function and a greater decrease in brain volume. The findings were published online in the journal Nature on March 8, 2022 [3].
"Using UK Biobank resources, we looked at changes in the brains of people with mild COVID-19 infections rather than moderate or severe infections. Although 96 percent of the subjects were less infected, at an average of 4.5 months after infection, the subjects had more gray matter volume and greater tissue damage. They also showed a much greater decline in their ability to complete complex cognitive tests. This change in cognitive level is associated with brain abnormalities. The negative effects of COVID-19 infection are more pronounced in older adults. Corresponding author Gwena lle Douaud said in an interview with the media [4], "In the future, we will continue to use brain imaging methods to monitor whether the above brain tissue damage can be recovered in the long run." ”
The paper analyzed cases from the UK Biobank, a total of 785 people (aged 15 to 81 years), all of whom underwent two brain scans (with an average interval of 38 months) and underwent cognitive tests. Of these, 401 (15 hospitalized) were detected for COVID-19 infection between two brain scans, with an average interval of 141 days between confirmed COVID-19 diagnosis and second brain imaging tests, and another 384 as age- and sex-matched controls.
The researchers compared all COVID-19-infected people (401), those who were not hospitalized (386), and 15 patients (15) with 297 olfactory-associated brain image phenotypes (IDP) in the control group (384). Based on three analyses, the researchers found a total of 68 significant differences in the infection group and the control group, and the difference between the two groups was between 0.2 and 2%, which was not very obvious. The four brain regions that differ the most are in the functional junction areas of the temporal piriform cortex and olfactory nodules, as well as the paracampal and lateral orbitofrontal cortex. The changes in brain imaging vary from individual COVID-19 patients to individuals, with 56% of patients having a piriformous cortical junction, 62% a olfactory nodule junction, 57% a left hippocampus, and 60% a left orbitofrontal cortex.
Image source: [3]
Figure 3 |
Through further analysis, the researchers found that the overall brain volume (Global measures of volume) and the left side of the cerebellum in the new crown pneumonia patients were also relatively smaller, and the thickness of the cingulate cortex was reduced, which was between 0.2 and 2% different from the control group. The biggest difference is in the paraepocampal gyrus and caudal anterior cingulate cortex, while the smaller left side of the cerebellum may be related to the reduced cognitive level of PATIENTS with COVID-19 found in the study.
It should be noted that the study also compared the difference between brain imaging changes in patients with common pneumonia and the corresponding control group, and also found some imaging characteristics of group-to-group differences, but did not overlap with the comparison results of new crown pneumonia. This also shows that the brain change data obtained in the study are all related to the new crown virus infection.
This is the only longitudinal imaging study to date comparing changes in brain tissue damage in PATIENTS with COVID-19 before and after infection, and the number of cases involved in the study is numerous. Judging from the current research data, the new crown virus infection does cause damage to the smell-related areas of the central nervous system in patients, although the magnitude of the change is moderate compared with the control group. The paper concludes by pointing out the limitations of the study, including the lack of strict grading of the patient's condition and the failure to identify the specific strain of the virus to which the patient is infected. At the same time, whether these brain injuries are caused by the spread of pathological damage or the virus itself, and whether the functions performed by the affected brain (e.g., the hippocampus responsible for memory) decline and whether they can be restored in the future still need further research.
bibliography:
[1] Hosp JA, Dressing A, Blazhenets G, et al,. Cognitive impairment and altered cerebral glucose metabolism in the subacute stage of COVID-19. Brain. 2021 May 7;144(4):1263-1276. doi: 10.1093/brain/awab009.
[2] Guedj E, Million M, Dudouet P, et al,. 18F-FDG brain PET hypometabolism in post-SARS-CoV-2 infection: substrate for persistent/delayed disorders? Eur J Nucl Med Mol Imaging. 2021 Feb;48(2):592-595. doi: 10.1007/s00259-020-04973-x.
[3] Douaud, G. et al. SARS-CoV-2 is associated with changes in brain structure in UK Biobank. Nature https://doi.org/10.1038/s41586-022-04569-5 (2022)..
[4] https://www.ox.ac.uk/news/2022-03-07-brain-regions-related-smell-show-decline-following-mild-covid-19
Plate editor| Lucas