Cytokine storms caused by severe COVID-19 can lead to long-term brain damage, including Alzheimer’s disease, US neurologists warn.
From the loss of smell to Alzheimer’s disease, the COVID-19 virus seems to be capable of anything. In a review of the literature published in the Journal of Alzheimer’s Disease, American scientists have summarized the effects of Covid-19 on the nervous system and proposed a three-level classification called “Neuro-COVID”.
Some patients admitted to hospital for COVID-19 “may develop cognitive decline, attention deficit, mental confusion or Alzheimer’s disease in the future,” warns Dr. Majid Fotuhi, neurologist and co-author of the paper, in a statement. The relationship between Covid-19 and neurological disorders can be summarized in two words: Cytokine storm. This runaway immune system, whose key molecules are called “cytokines” which has been frequently mentioned since the beginning of the pandemic, is more harmful than the virus itself and has caused many deaths. The SARS-CoV-2 virus penetrates our cells, in particular thanks to a protein that they all have on their surface in varying amounts, the ACE2 receptor. The concern is that by occupying this receptor, the virus will make it inaccessible to fulfill its primary functions which are very numerous. The inaccessibility of ACE2 is therefore associated with narrowing of blood vessels, kidney failure, heart disease, cell death (apoptosis), and oxidative processes that accelerate the aging process and promote brain degeneration, the authors list in the publication.
cytokine storm can lead to brain degeneration
The out-of-control immune system itself can cause an inflammation of the nervous system, up to encephalopathy (inflammation of the brain). In addition, neurons are rich in ACE2, which makes them susceptible to infection with SARS-CoV-2. The latter, like other coronaviruses, can remain in certain neurons without acute toxicity and cause long-term functional disorders, the authors explain. Abnormal protein production in patients who survive and recover from their severe COVID-19 “can therefore theoretically lead to brain degeneration decades later.
French studies have reported that 84% of the 48 patients in the Strasbourg intensive care unit with Covid-19 have positive neurological examination abnormalities and that 33% of the patients leaving the intensive care unit have residual symptoms such as attention deficits and difficulties in decision making and behavioral control.
Three stages of NeuroCovid
The authors propose the following classification of NeuroCovid:
NeuroCovid stage 1: Loss of taste and smell: The attack of the SARS-Cov2 virus is limited to the ACE2 receptors on the nasal epithelial cells and the taste. The storm of cytokines activated by the virus remains weak and controlled, and patients usually recover without any intervention.
Stage NeuroCovid 2: Cytokine storm: The SARS-Cov2 virus activates a strong immune response with high cytokine levels and triggers the formation of blood clots that settle in the vessels. Therefore, patients may suffer a stroke or arterial or venous occlusion (thrombosis).
NeuroCovid stage 3: Severe cytokine storm: The immune overload caused by the virus damages the blood-brain barrier the filter that protects the brain by allowing inflammatory factors and other blood contents (including virus particles) to enter the brain. The patient suffers the resulting brain damage, which leads to delirium, encephalopathy, or seizures.
“Very likely” long-term neurological consequences.
It is “very likely” that the cytokine storm and the brain damage it causes (stroke, blood-brain barrier damage, and severe inflammation) “will have long-term neuropsychiatric consequences,” the researchers conclude. They predict that “health systems around the world” may experience “in the next few years” a surge of patients with depression, post-traumatic stress disorder, anxiety, insomnia, psychosis, but also cognitive impairment or decline such as Alzheimer’s disease. “As noted in SARS-CoV-1 (2002 SARS epidemic, editor’s note) and MERS (2012 epidemic, editor’s note), not all patients with Covid-19 infection who leave the hospital will recover 100% of their basic emotional and neurocognitive functions. Since some of the effects of SARS-CoV-2 can theoretically occur “months or years after infection”, continuous follow-up with affected patients will be required.