The neurological symptoms of COVID-19

Although SARS-CoV-2 principally targets the respiratory system, COVID-19 patients may also suffer from neurological and psychiatric symptoms. These symptoms may range from loss of smell or headaches to encephalitis or stroke. These neuropathologies may be the direct consequence of brain cells being attacked by the virus, or an indirect consequence of the peripheral immune response. Researchers at the Universities of Stanford (USA)and Saarland (Germany) have analysed brain cells in order to understand these neurological changes.

The researchers studied the transcriptome (level of gene expression) of more than 65 000 brain cells from 8 COVID-19 patients and 14 control patients. They firstly observed that cells in the blood-brain barrier of infected patients were inflamed. Since no RNA trace of the virus was found in the brains, the misfunctioning observed was therefore not a direct consequence of infection in the cerebral cells. But inflammation in the blood-brain barrier sends a signal to nerve cells, thereby disturbing cognitive function.

In addition, the researchers detected T lymphocytes in the brains of all COVID-19, patients, but none in the non-infected group. These T cell infiltrations may also provoke neuro-inflammation and damage neurogenesis (renewal of neurons). Finally, they observed that the condition of certain nerve cells in infected patients is comparable to that of patients suffering from neurodegenerative illnesses.

The neurological and psychiatric consequences observed in COVID-19 patients may therefore be the consequence of inflammation in the brain cells, and not directly due to attacks by the SARS-CoV-2 virus. The recent emergence of COVID-19 and our lack of clear perspective on the illness and its consequences mean that other neurological symptoms may yet be discovered, notably in cases of long COVID.