(Paris) Two recent studies provide possible explanations for the causes of long-term COVID-19, a syndrome with still mysterious mechanisms, one evoking the joint effect of after-effects in various organs, the other a mechanism at neuron level.
There is “concrete evidence that different organs undergo changes” after hospitalization linked to COVID-19, Christopher Brightling, co-author of a study published Friday in the Lancet Respiratory Medicine.
This work is based on MRIs performed on 259 patients who were hospitalized for COVID-19 in 2020-2021. They were compared with examinations carried out on around fifty people who had never been infected.
Nearly a third of COVID-19 patients had “abnormalities” in multiple organs, several months after discharge from hospital. These organs include the brain, lungs or kidneys and, to a lesser extent, the heart and liver.
Researchers have, for example, identified lesions in the white matter of the brain, a phenomenon which can be associated by scientific literature with a slight cognitive decline.
For the authors of the study, as well as independent observers, these results open up a possible explanation for long COVID-19, that is to say the persistence of lasting after-effects several months after infection.
This disorder, which however lacks a consensual definition, is still poorly understood on a physiological level, with several explanations competing without being necessarily exclusive.
The study made public on Friday suggests that long COVID-19 “is not explained by serious insufficiencies concentrated in a single organ” but rather “an interaction between at least two abnormalities of [différents] organs,” says pulmonologist Matthew Baldwin, who did not participate, in the same issue of Lancet Respiratory Medicine.
PHOTO PATRICK SANSFAÇON, LA PRESSE ARCHIVES
The brain trail
Another study, published a week earlier in the journal eBiomedicinerather opened the trail of a mechanism concentrated in the brain.
Led by a team from INSERM, the French National Institute of Health and Medical Research, this study looked at around fifty patients, some of whom suffered a drop in their testosterone levels, linked to an alteration by the virus of certain neurons regulating reproductive functions.
The researchers then measured the cognitive functions of these patients, only to note poorer performance when this category of neurons was affected.
These results “suggest that the infection can lead to the death of these neurons and be the cause of certain symptoms which persist over time,” says INSERM in a press release.
Fatigue, cough, shortness of breath, intermittent fever, loss of taste or smell, difficulty concentrating, depression… long COVID-19 manifests itself by one or more symptoms from a long list, generally within three months after infection and persisting for at least two months. Symptoms that cannot be explained by other diagnoses and have an impact on daily life.
In France, “long COVID-19” has affected 4% of adults or 2.06 million people over the age of 18, with a small proportion (1.2%) declaring that they are seriously hampered in their daily activities, according to a study. of Public Health France carried out last fall and the results of which were revealed in June.
The vast majority of patients (90%) suffering from long-term COVID-19, however, see their symptoms slowly improve after two years, with the others experiencing rapid improvement or, on the contrary, persistence of their disorders, specifies a study published in May. by the Dr Viet-Thi Tran, epidemiologist (Université Paris Cité/AP-HP), with 2197 patients from the “ComPare” cohort suffering from long-term COVID-19, followed regularly.