In a significant percentage of people who have survived COVID, nervous system symptoms persist for many months.
Acute neurological disorders
The COVID-19 pandemic, announced in March 2020, was an event that shook not only the health care system, but all of economic and social life. We were facing the situation of a pandemic for the first time, and no one knew what was ahead, which caused justifiable fear. The stress of contracting an unknown disease was so severe that it could lead to various neurological and psychological complications, such as mood and cognitive disorders, i.e. deterioration of memory and concentration, among others. Quite quickly, however, it became clear that these were not the only neurological symptoms accompanying the infection.
According to a study conducted by the European Academy of Neurology, acute neurological abnormalities in COVID-19 include:
- encephalopathy,
- stroke,
- headache,
- loss of sense of smell,
- peripheral nerve disorders.
Risk factors for acute neurological disorders in COVID-19 are:
- older age,
- male sex,
- previous history of neurological conditions.
In patients hospitalized for severe COVID-19, the appearance of acute neurological disorders is associated with an almost 6-fold increase in the risk of death during hospitalization. It also raises the question – do neurological symptoms disappear with the cessation of infection, or do they become a problem for longer?
SARS-CoV-2 virus and the nervous system
The data cited above led researchers to wonder whether the SARS-CoV-2 virus enters the nervous system, and if so, by what route. This is because, in general, coronaviruses are not neurotropic viruses, but attack mainly the respiratory system. On the other hand, it is known that ACE-2 receptors, which are targeted by the SARS-CoV-2 virus, are also found on glial cells of the brain and spinal cord neurons.
Neurological manifestations of post-COVID
Post-COVID are long-term – lasting more than 3 months – health effects associated with
associated with surviving SARS-CoV-2 virus infection.
Post-COVID symptoms include:
- chronic fatigue syndrome,
- olfactory disturbances,
- memory problems,
- cough,
- gastrointestinal disorders,
- dysautonomia (i.e., dysfunction of the autonomic nervous system, which can cause palpitations, changes in blood pressure, thermoregulation problems, excessive sweating or sexual dysfunction, among other things),
- intolerance of physical exertion,
- mental disorders.
Many of these, therefore, involve the nervous system, and worryingly, post-COVID syndrome occurs in a significant percentage of patients.
American study
A large U.S. study involving nearly 240,000 post-COVID SARS-CoV-2 patients found that 34% of patients had a neurological or psychiatric diagnosis within 6 months of contracting COVID-19, and the rate was as high as 46% in those with severe COVID requiring hospitalization. The results of this study were published in the prestigious journal Lancet Psychiatry (2021; 8(5): 416-427). A follow-up to this study, also published in Lancet Psychiatry (2022; 9(10): 815-827), which had already included a group of nearly 1,200,000 post-COVID patients, showed that the risk of cognitive deficits (brain fog), dementia, psychosis and epilepsy was still higher after 2 years in the post-COVID group than in the in the control group.
SARS-CoV-2 virus and olfactory impairment
By far the most common neurological complication of COVID-19 is olfactory disorders, affecting as many as 60% of those undergoing the infection. These disorders include a complete loss of smell (anosmia), a reduced ability to smell odors (hyposmia) or a disorder in which the patient perceives various odors quite differently than they actually smell (parosmia).
What causes these disorders? As it appears today, the SARS-CoV-2 coronavirus attacks so-called support cells, which are part of the olfactory epithelium and support the functioning of olfactory neurons, facilitating their reception of olfactory stimuli. This means that coronavirus usually does not directly damage neurons, but destroys support cells, which have the ability to regenerate. Therefore, in most patients, olfactory disturbances are transient and pass after a maximum of six weeks.
In addition to olfactory disorders, SARS-CoV-2 virus infection can have other long-term and serious health consequences, such as:
- immune changes in the patients’ cerebrospinal fluid, absent in healthy individuals;
- damage to the blood-brain barrier;
- formation of microthromboses, including in brain vessels;
- “cytokine storm,” which can affect neurotransmission in the brain, resulting in depression, chronic fatigue, anhedonia (i.e., loss of the ability to feel pleasure) and complaints of pain. These are symptoms typical of post-COVID.
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