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Advanced Neurology Neurological complications of COVID-19

Table 1. Neurological complications associated with many subtypes of COVID-19, and these subtypes differ in
COVID‑19 and their prevalence many aspects, such as virulence and transmissibility, which
explain the variability in the mechanisms. A study found
Neurological complications Occurrence rate
that convulsions could be a sign of the Omicron variant in
Gustatory dysfunctions [9] 49% of COVID-19 patients children with COVID-19 . Another study on children with
[83]
Olfactory dysfunctions [9] 65% of COVID-19 patients COVID-19 found that the Omicron variant is more likely
Stroke [45] 1.5% of COVID-19 patients to be associated with neurologic manifestations such as
[84]
Memory impairment [23] 12.5% of COVID-19 patients seizures compared with other COVID-19 virus variants .
Muscle injury [13] 16% of COVID-19 patients However, there is still a lack of multicenter and forward-
Epilepsy [51] <1% of COVID-19 patients looking research on the neurological complications caused
Headache [13] 15% of COVID-19 patients by specific COVID-19 virus variants.
Dizziness [85] 9% of COVID-19 patients 4. Conclusion
Nausea and vomiting [86] 5% of COVID-19 patients
Despite being a disease primarily affecting the respiratory
system, COVID-19 has gradually attracted attention as
On the one hand, after infecting the respiratory a disease accompanied by the unexpected neurological
system, SARS-CoV-2 can enter the bloodstream by complications, evidenced by a growing number of studies
infecting endothelial cells in the choroid plexus blood- (Table 1). In this review, we summarize the symptoms,
brain barrier or blood-CSF barrier in the choroid plexus. characteristics, and mechanisms underlying the neurological
Furthermore, SARS-CoV-2 can infect leukocyte and cross complications of COVID-19. The neurological complications
the barriers to invade the CNS so as to spread throughout of COVID-19 patients include CNS complications, such
the body with leukocyte . In this process, leukocytes as brain function decline, cerebrovascular disease and
[76]
release pro-inflammatory factors, such as tumor necrosis dysgeusia, as well as PNS complications. Some of these
factor, interleukin (IL)-1β, IL-6, IL-12, and even cause complications are reversible, but others could be life-
cytokine storm, which can destroy oligodendrocytes and threatening. The SARS-CoV-2 infection in the nervous
neurons . The integrity of the blood-brain barrier may be system is mediated by the binding of the virus to the ACE2
[77]
compromised by cytokine-driven damage and immune- receptor or its replacement receptor, which leads to a chain
mediated toxicity . Taken together, SARS-CoV-2 binds to of inflammatory responses. This review provides reference
[78]
the ACE2 receptor, which, in turn, induces an inflammatory contents for understanding the heterogeneous neurological
cascade that ultimately destroys the neurons. symptoms and manifestations as well as potential neurological
On the other hand, SARS-CoV-2 could also enter the CNS complications of COVID-19. A deeper understanding of
through OB. OB is often considered an immune organ that these manifestations and complications can help make
can prevent viruses from entering the CNS, but its dysfunction appropriate treatment decisions that would directly reduce
may lead to an infection of the CNS . A previous study has morbidity and mortality among the patients. Finally, more
[79]
confirmed that virus can penetrate the olfactory epithelium investigations should be carried out to determine the broad
into the brain and cause death in the mice . Meanwhile, a spectrum of neurological symptoms and the underlying
[80]
recent study showed that olfactory epithelial cells express pathophysiological mechanisms of COVID-19.
ACE2, allowing viruses to infect the cells through a Acknowledgments
replacement receptor . OB MRI studies showed that MRI
[18]
signal changes were consistent with virus invasion of OB and This research was supported by the National Natural
cortical regions , suggesting that SARS-CoV-2 may invade Science Foundation of China (81920108017, 82130036),
[80]
human CNS from the external environment through OB. the Key Research and Development Program of Jiangsu
Province of China (BE2020620). Jiangsu Province Key
Fecal-oral route is hypothesized as a potential route of
transmission for SARS-CoV-2 on the grounds of the high Medical Discipline (ZDXKA2016020).
expression of ACE2 in gastrointestinal system , and the Conflict of interest
[81]
nervous system injury caused by indirect immune-mediated
cytokine storm could be another possible mechanism The authors have no competing interest to declare.
of nervous system complications . Further and more Author contributions
[82]
detailed research is needed to investigate the mechanism
of how SARS-CoV-2 affects the nervous system and causes Conceptualization: Yun Xu
neurological complications. It is worth noting that there are Data curation: Chenglu Mao, Qiaochu Guan, Huahong Zhu

Volume 1 Issue 2 (2022) 6 https://doi.org/10.36922/an.v1i2.83