Covid-19 is responsible for a variety of symptoms – breathing difficulties, fever, dry cough… But neurological signs have also been observed as soon as the virus appears, such as: headaches, delirium or confusion, cognitive dysfunction, fatigue and of course, loss of smell (anosmia) and taste. The disease could even cause strokes.
From April 2020, i.e. at the very beginning of the pandemic, a study published in the specialized journal JAMA Neurology reported that, of 214 patients from Wuhan (China) with Covid-19, 36% had neurological symptoms. Among these: loss of smell, nerve pain, seizures or strokes. Same observation in the New England Journal of Medicine where Strasbourg doctors noted that, out of 58 patients with Covid-19, 40 presented with abnormal agitation, 26 suffered from mental confusion, and around a third presented with disorientation, inattention or poorly controlled movements.
In short, since the quasi-start of the pandemic, the neurological disorders associated with Covid have been regularly mentioned by scientists. A new international study that examined more than 16,000 patients hospitalized with covid infection but who were otherwise healthy, indicates that 13% of patients developed serious neurological conditions. This study led by Dr. Anna Cervantes Arslanian of the Boston School of Medicine (USA) examined patients of 179 hospitals in 24 countries. They counted 1656 (10.2%) patients with encephalopathy (any diffuse brain disease that impairs brain function or structure) at admission. In addition, 331 (2%) had a stroke, 243 (1.5%) had a seizure and 73 (0.5%) had meningitis or encephalitis on admission or during hospitalization.
Moreover, they found that all these severe neurological manifestations were associated with increased disease severitygreater need for intensive care interventions, longer length of stay and higher mortality.
Overall brain size decreased
Another study, published in review Nature on March 7, 2022, confirmed the deleterious effects of Covid on the brain, including in the case of mild forms of the pathology.
The interest of this study is that the researchers compared the images of the brain of patients previously infected with Covid (most of whom had had mild forms) with the “benchmark” images of these same people taken several years before. the appearance of Covid, as part of an operation carried out by Biobank, an organization that has been compiling health data in the United Kingdom for years.
In total, the brain changes of 785 participants in the biobank (aged 51 to 81) were therefore compared. What are the results ? Former Covid patients have generally seen the thickness of the gray matter of the brain decreases and the overall size of the brain decreases. On average, an infection with the virus results, several months later, in a loss or lesion of 0.2% to 2% of brain tissue in addition to what is observed in non-humans. sick.The infected participants also showed on average a greater cognitive decline between the two imagings (before and after infection).
In addition, the researchers observe that after a Covid infection, the areas of the brain most affected are those linked to the perception of odors.
Should we be worried about the neurological effects of Covid?
To get an idea of the magnitude of these effects, they can be compared to what happens during normal aging : we know that people lose every year between 0.2% and 0.3% of gray matter in regions linked to memory”, explains Gwenaëlle Douaud, the main researcher who contributed to this study, in a presentation on her website. So there is no need to panic. Especially since the study does not make it possible to conclude either on the mechanisms of these cerebral lesions or on their irreversibility.
Note, however, a vast study conducted by researchers at Imperial College London: they had analyzed the results of cognitive tests of 84,285 people who contracted Covid-19 or suspected of having contracted it. The results of this study conducted in 2020, and led by Professor Adam Hampshire, of the Imperial college brain sciences laboratory, indicate that patients who have suffered from a severe form of Covid-19, “obtain worse results on cognitive tests in more areas than you would expect given their age”. A drop in performance equivalent to 10 years of brain aging.
What are the avenues envisaged to explain these neurological effects?
A study by Erasmus University Rotterdam (Netherlands) published in June 2021 in the journal Spherehad already shown that the virus could attack the brain and be the cause of neurological and psychological complications in some patients. “Even though SARS-CoV-2 is rarely detected in the central nervous system or cerebrospinal fluid, evidence is mounting that covid could enter the brain via the olfactory nerve“says Prof. Debby van Riel from the Department of Viroscience at the University of Rotterdam. “However, what happens after the virus enters the central nervous system is still poorly understood. the immune system probably also plays a role.
Another study, published in November 2020 on the Jama networkhad demonstrated that Covid-19 had consequences on the brain of patients, manifesting itself in particular in older patients (whose immune system is less efficient) by a “mental fog”. “Delirium – or confusion, disorientation, or other cognitive changes – may be a common sign of infection in older people, whose immune systems react differently to viruses and bacteria,” the doctors explained..
One of the hypotheses retained by the researchers is indeed that of thecytokine storm. Clearly: faced with infection by Sars-Cov-2, the body would trigger a disproportionate defense reaction: too extreme, it could lead to “overheating” of the brain… and specific neurological symptoms.
Another hypothesis: d‘after a recent Inserm study (October 2021), the SARS-CoV-2 coronavirus would be capable of attack the blood vessels of the brainand more particularly at the blood-brain barrier. By studying the cortex of patients who died following an infection with SARS-CoV-2, the researchers discovered that the virus was able to manufacture “scissors” capable of “cutting” particular proteins: the NEMO proteins. However, these proteins are essential for the survival of endothelial cells in the brain: they therefore end up dying. Dead, the vascular endothelial cells of the brain can no longer play their protective and irrigation role. Result: we see the appearance of “ghost ships” in the brain, that is to say empty “tubes” which no longer transport blood. L’ “attack” of the SARS-CoV-2 coronavirus on the endothelial cells of the brain could lead to the development of cognitive or neurodegenerative disorders, or even to dementias.
Sources :
- Neurologic Manifestations of Severe Acute Respiratory Syndrome Coronavirus 2 Infection in Hospitalized Patients During the First Year of the COVID-19 Pandemic, Critical care exploration, April 2022
- SARS-CoV-2 is associated with changes in brain structure in UK Biobank, NatureMarch 2022.
- Inserm, October 2021.
- Replication Kinetics, Cell Tropism, and Associated Immune Responses in SARS-CoV-2- and H5N1 Virus-Infected Human Induced Pluripotent Stem Cell-Derived Neural Models, mSphereJune 2021.
- Delirium in Older Patients With COVID-19 Presenting to the Emergency Department, JAMA, November 2020.
- Cognitive deficits in people who have recovered from COVID-19 relative to controls: An N=84,285 online study, EClinicalMedicine, October 2020.
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