Could Covid decrease brain size?

[Mis à jour le 10 mars 2022 à 17h30] To the known symptoms of Covid-19 (fever, cough, cold, etc.) were added neurological signs specific to infection such as loss of taste and smell (without there being any associated cold, therefore a stuffy nose). Covid-19 infection, even mild, would also decrease the overall size of the brain and the amount of gray matter in regions related to smell and memory according to a study published in the journal Nature on March 7, 2022. This study involved 785 UK adults aged 51-81. The researchers found significant differences in MRI scans taken before and after infection. More than half of the participants tested positive for Covid-19 between the two scans. The researchers compared these funds to the group that had not been infected with the coronavirus.

“Infected participants also showed cognitive decline on average”

They observed in the former a greater reduction in the overall size of the brain, a greater reduction in the thickness of the gray matter, a atrophy and damaged tissue in regions related to smell and mental faculties. “Infected participants also showed on average greater cognitive decline between the two time points.” underlines the study. In France, the Director General of Health, Pr Jérôme Salomon, confirmed in April 2020 than “neurological lesions are often observed in Covid-19 patients in intensive care, (lesions) sometimes transient, sometimes permanent“. In a study by Akiko Iwasaki, an immunologist from Yale University, published in 2021 in the magazine Journal of Experimental Medicine, the researchers confirmed “evidence of neuroinvasive capacity of SARS-CoV2 (particularly based on observations in the autopsies of deceased Covid-19 patients) and an unexpected consequence of direct infection of neurons by SARS-CoV-2”. The Covid-19 disease virus is therefore quite capable of invading the brain and replicating itself there.

How does the virus infect the brain?

The Sars-Cov-2 virus, like other human coronaviruses, has a neuroinvasive and neurotropic potential. Several studies are being conducted to try to understand how this new virus attacks the brain region.

► The study published on March 7, 2022 shows that even mild covid-19 infection would decrease overall brain size and the amount of gray matter in regions related to smell and memory. “These brain imaging results may be the in vivo markers of a degenerative spread of disease through the olfactory pathwaysofneuroinflammatory events [maladies inflammatoires du cerveau] or the loss of [traitement de l’information sensorielle] due to anosmia” according to the researchers of the study.

►The study published in October 2021, co-carried out by Inserm, the University, the CHU and the Institut Pasteur de Lille and colleagues from the CNRS indicates a direct effect of Sars-CoV-2 on brain blood vessels. Researchers have discovered that Sars-Cov-2 makes, from its own genetic material, molecular scissors which will cut a protein called NEMO, essential for the survival of endothelial cells which will therefore die. However, the endothelial cells of the brain make up the blood-brain barrier (BBB) ​​whose main function is to isolate the central nervous system and the blood circulation to prevent the penetration of foreign substances or toxic molecules into the brain. These same cells also allow the transfer of essential nutrients for the proper functioning of the brain. When they die, these cells can no longer perform their function.

►The study of January 2021, co-carried out by researchers from Yale University (USA), Sorbonne University, Inserm and CNRS at the Brain Institute as well as the Pitié-Salpêtrière Hospital AP-HP attests to the ability of SARS-CoV-2 to enter neurons and use their components to multiply, causing metabolic changes in infected cells, without destroying them. The neighboring cells of the infected neurons see themselves deprived of oxygen and end up dying. How does the virus do? Earlier data showed that in the rest of the body, the virus used the ACE2 protein, present on the cell surface. This is particularly expressed in the lungs, explaining why the virus attacks this organ more specifically. However, this entry pathway remained to be demonstrated in neurons. In the January 2021 results, the researchers confirm its importance for brain cell infection. “Neural infection can be prevented by blocking ACE2 with antibodies or administering cerebrospinal fluid from a COVID-19 patient” they indicate.

What are the neurological effects of Covid-19?

The neurological damage linked to Covid-19 is diverse, ranging from mild and transient signs such as loss of taste and smell to more serious cases such as seizures, cerebrovascular accidents (CVA) and encephalopathies. The latest study published in March 2022 reveals that covid-19 infection, even mild, would decrease the overall size of the brain and the amount of gray matter in regions related to smell and memory and cause atrophy. “Infected participants also showed on average a cognitive decline more important between the two times [IRM]These effects on the brain were noticed more pronounced in the elderly and those who were hospitalized but they are also present in patients who have only a mild form of the disease or the asymptomatic. These effects do not appear to be irreversible but research continues. The October 2021 study reveals that the impact of the coronavirus on endothelial cells can cause two consequences:

• From microhemorrhages in areas where blood is not supposed to have free access
• A hypoperfusion of certain regions of the brain (decreased blood flow which can lead to the death of patients in the most serious cases)

A study published on April 1, 2020 in the Journal Radiology thus reported the case of a 60-year-old American woman who tested positive for Covid-19 and who presented acute necrotizing hemorrhagic encephalopathy. Is a rare neurological disease characterized by the onset of seizures, an altered state of consciousness, neurological decline and varying degrees of kidney dysfunction. Doctors also report cases of patients presenting with loss of bearings, delusions even before developing fever or respiratory disease, observes Dr. Alessandro Padovani who opened a NeuroCovid unit to treat patients with neurological disorders at the University of Brescia hospital in Italy. In the United States, a neurologist from the Long Island Jewish Forest Hills Hospital, Rohan Arora makes the same observation: “We see many patients in confused states” he declared to our colleagues from theAFP. He claims that 40% of coronavirus survivors are affected, while ignoring whether these disorders are lasting. The passage in intensive care can cause confusion, in particular because of the drugs. But the neurologist notes that the back to normalfor Covid-19 patients, appears to take longer than for those who have survived a heart attack or stroke.

Sources :

SARS-CoV-2 is associated with brain structural changes in the UK Biobank. Nature Review, March 7, 2022.

The main protease M pro of SARS-CoV-2 causes microvascular brain pathology by cleaving NEMO in brain endothelial cells. Nature Neuroscience Journal. October 21, 2021.

Neuroinvasion of SARS-CoV-2 in human and mouse brain. January 12, 2021. YWAM.

Results confirm the ability of SARS-CoV-2 to infect neurons. Inserm. January 13, 2021.

First case of brain damage due to Covid-19 at the MRI, Department of Radiology, at the Henry Ford Health System in Detroit (USA), Journal RadiologyApril 1, 2020.

Institut Armand-Frappier, laboratory of neuroimmunovirology, “Human respiratory neuro-invasive and neurotrophic coronaviruses: potential neurovirulent agents, 2014, available in the John Libbey Review.

Journal of Medical Virology, Neuroinvasive potential of SARS-CoV2 may play a role in respiratory failure in Covid-19 patients, February 27, 2020.

MedRxivNeurological manifestation of patients hospitalized with Covid-19 in Wuhan, China, February 25, 2020.