As the Covid-19 epidemic was in full swing, general practitioners reported that an increasing number of patients infected with the virus came to their offices complaining of poor attention and memory loss. These cognitive problems have been largely attributed to fatigue.
However, another hypothesis is emerging: these symptoms could also be directly linked to the presence of the SARS-CoV-2 coronavirus in the central nervous system, in other words the brain and spinal cord.
Coronaviruses can attack various organs
So far, Covid-19 has mainly been associated with breathing difficulties, with the virus primarily affecting the lungs. However, scientific work has already revealed that beyond the respiratory tract, coronaviruses have the ability to spread to other organs, including the brain.
Studies carried out following the epidemic of severe acute respiratory syndrome (SARS) in 2003 have thus made it possible to highlight the presence of viral genome in the cerebral cortex of patients. In individuals infected with MERS-CoV, lesions have been observed in several cerebral regions, especially in the frontal and parietal lobes. However, the data concerning the long-term effects of this family of viruses on the brain, and the consequences on the cognitive functioning of individuals, remain patchy.
In order to take stock of the available knowledge, we carried out a literature review, published in the journal Brain Communications. We describe the lines of research to be pursued to better understand the link between the brain, psychiatric and neurological difficulties and epidemics of coronavirus.
Drawing attention to this topic is of utmost importance in order to improve and strengthen the long-term follow-up of people who were exposed to SARS-CoV-2 during the pandemic.
The seahorse, a particularly vulnerable region?
Studies carried out on animal models particularly highlight the fragility of the hippocampus, an area of the brain that plays an important role in memory and spatial navigation. This vulnerability is not only observed in the context of a coronavirus infection, but also in the context of other respiratory infections. For example, studies carried out in mice infected with the influenza virus have revealed the occurrence of morphological and functional changes in the hippocampus in these animals. These are associated with a degradation of spatial memory over the long term.
In the case of SARS-CoV-2, several questions arise: can such changes be observed in the hippocampus of certain patients? If so, are they a direct result of the viral infection? Research still needs to be done to find the answers.
It will also be necessary to determine whether such brain changes could accelerate the development of other pathologies, such as Alzheimer’s disease, which is characterized precisely by a deterioration of the hippocampus and a deterioration of spatial memory.
Patients requiring ventilation are more affected
Another concern is severe acute respiratory syndrome, which occurs in the most severe cases of Covid-19 and requires mechanical ventilation to assist breathing.
We know that more than 70% of hospitalized patients whose condition requires mechanical ventilation, due to various respiratory pathologies, see their cognitive performance, their attention span, their memory and their fluency in language, and this up to a year after discharge from hospital.
In addition, it has been argued that certain brain alterations (especially atrophy of the brain) associated with problems of attention, verbal memory and executive functions (logic, planning reasoning, etc.) which affect patients suffering from a syndrome. severe acute respiratory failure could be explained by a lack of oxygen (hypoxia) occurring before ventilation.
Viral psychiatric disorders?
We were also interested in the scientific literature on the links between psychiatric illnesses and human coronavirus infections.
A small study, conducted on 40 patients suspected of being infected with MERS-CoV and quarantined for this reason, notably revealed psychiatric disorders, including psychotic events and hallucinations, in 70.8% of them. The fact that, in this work, all patients suffering from these disorders were then tested positive for the virus (while the suspected cases tested negative showed no cognitive sign) suggests the existence of a potential viral mechanism.
Following the Covid-19 pandemic, of an unprecedented scale, an increase in the prevalence of psychiatric disorders in the general population is expected, due to the trauma caused by this period. However, we cannot exclude that among these cases, some were directly triggered by the viral infection, which would have been responsible for cerebral modifications, rather than by environmental factors, such as the anxiety-provoking climate in which we evolved for several months.
Data on the ability of the new coronavirus to spread to the central nervous system is accumulating and it seems that the risk of harmful consequences on the brain in the longer term is far from zero. It is therefore urgent to consolidate research on this subject. In particular, larger studies are needed, focusing on brain dysfunctions that affect populations that have been exposed to previous coronavirus epidemics.
In the coming months, special attention should also be paid to the cognitive manifestations linked to SARS-CoV-2 infection: assess their diversity, establish the duration of any cognitive symptoms in former patients, identify the links between severity of infection and severity of cognitive impairment, etc.
As such, the participation of general practitioners will be essential. They are in fact the most able to follow patients and identify those who have cognitive problems in the long term.
The original version of this article was published in The Conversation.
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