Scientists link loss of sense of smell in COVID-19 to brain damage.
COVID-19 leads to the loss of gray matter in the brain, British experts warn. This may be the cause of loss of smell and taste and other neurological symptoms. The body can adapt to the changes, and the symptoms will pass, but the brain tissue itself will not recover.
The causes of neurological symptoms in COVID-19 may be the destruction of gray matter, according to researchers from the University of Oxford. They told us more about this in an uncensored article posted on the medRxiv preprint service.
The researchers used data from the UK medical and genetic information repository UK Biobank. They selected the results of examinations of 394 people who had been ill with coronavirus and had MRI scans of the brain both before and after the disease and compared them with the results of a control group of 388 people who had not been ill.
The ability to look at the patient’s brain before and after the disease allowed us to distinguish the changes caused by COVID-19 from other possible brain lesions, the researchers note.
They revealed a significant loss of gray matter density and volume in several brain regions — the parahippocampal gyrus, which is associated with memory encoding, the lateral orbitofrontal cortex, which is involved in decision-making, and the insular lobe, which plays a role in the formation of emotions.
“Our results show a loss of gray matter in the limbic regions of the cerebral cortex directly associated with the primary olfactory and taste systems,” the authors write.
More pronounced changes were observed in the left hemisphere.
The researchers also compared the results of hospitalized patients with those who were ill at home but found no significant difference. However, in hospitalized patients, there was a more pronounced loss of gray matter in the cingulate cortex, the central nucleus of the amygdala, and some regions of the hippocampus. All these areas are also associated with memory and the formation of emotions.
COVID-19, even in a mild form, can lead to brain damage, the researchers conclude.
They recommend that those who have been ill do not neglect timely examinations to find out what consequences they could face.
The design of the study does not allow us to confirm the presence of a causal relationship — theoretically, some other factors could have influenced the state of the brain. Nevertheless, the authors of the work are sure that this connection exists. They note other limitations of the work: almost all of the patients were white, which does not allow the data to be extended to representatives of other ethnic groups, in addition, the researchers did not have data on the oxygen saturation of the participants ‘ brains and other factors that could play a role.
“We were able to identify a consistent pattern of gray matter loss in the limbic regions of the brain that form the olfactory and taste networks,” the researchers conclude. Whether these abnormal changes indicate the spread of the disease in the brain, which may portend future vulnerability of the limbic system, including memory, in these patients, remains to be seen.”
“The study suggests that COVID-19 can lead to loss of brain tissue, and this will have long-term consequences,” says Dr. Scott Gottlieb, former head of the US Food and Drug Administration.
The body will be able to compensate for this over time, and the symptoms will disappear, but it will never be possible to restore the destroyed areas.”
The decrease in brain volume was observed in areas close to those associated with the sense of smell, Gottlieb emphasizes.
“This shows that the loss of sense of smell is a consequence of a more important process, a reduction in the volume of the cerebral cortex,” he says.
Also, COVID-19 can lead to the defeat of the white matter, experts from the University of Pennsylvania found out earlier. Of the 2,820 COVID-19 patients treated by the authors between March 1 and June 18, 2020, 59 underwent brain MRI. Many showed signs of brain damage caused by multiple sclerosis, strokes, lack of oxygen in the blood, the insufficient blood supply to the brain, and other factors. But the researchers also noticed that six patients (10.2%) showed signs of leukoencephalopathy.
Leukoencephalopathy is a persistent breakdown of the white matter of the brain. With progression, it can lead to speech and vision disorders, less often to dizziness, headaches, and epileptic seizures. Mental disorders are also possible.