Although we usually think of it as primarily a respiratory tract disease, neurological manifestations with Covid-19 are not at all uncommon,^1-6 occurring in over one-third of hospitalized patients with Covid-19 according to one medRxiv report.¹

In a Chinese study¹ involving 214 hospitalized patients with Covid-19, 36.4% had 1 or more neurological symptoms, with the majority involving the central nervous system (CNS) (25.0%), of which the most common complaints were dizziness (17%) and headache (13.0%). Some patients (9.0%) had cranial nerve/peripheral nerve complaints of which the most common were difficulty with taste (hypogeusia) (6.0%) and sense of smell (hyposmia) (5.0%).  A fewer number of patients had impaired consciousness, acute cerebrovascular disease (including ischemic stroke and cerebral hemorrhage). Although not strictly-speaking a neurological manifestation, the study also reported “muscle injury” in ~20.0% of patients     (defined as myalgia plus CK >200 IU/L).

Descriptions of Covid-19 encephalopathy, including one associated with acute hemorrhagic necrotizing process, are also beginning to appear in the literature.^3-5 Reports of “Neuro-Covid-19 units” in Italy further underlines the common occurrence of neurological symptoms in these patients.⁶

More than one mechanism for neurological complications in Covid-19 are likely,  including:^1-2

1. Direct viral invasion into the CNS which could explain the associated headache, high fever, vomiting, convulsions, and consciousness disorders. Some have reported normal CSF parameters but a report of PCR positive CSF suggests direct injury from the virus itself.² Covid-19 virus may gain access to the CNS through direct invasion of neuronal pathways (eg. olfactory nerve given recent reports of difficulty with sense of smell) or through blood circulation.
2. Indirect CNS injury through extreme systemic derangements such as hypoxia, or immune/inflammatory response-related injury (eg, through cytokines, hypercoagulability related to infection). Some have also posited that binding of Covid-19 virus to ACE2 may cause abnormally elevated blood pressure and increase the risk of cerebral hemorrhage.²

The fact that Covid-19 is so versatile and affects the nervous system as well shouldn’t surprise us. Neurological complications have been reported with couple of other related respiratory Coronaviruses such as those of SARS and MERS.²

 

Bonus pearl: Did you know that as early 1970-80s some coronaviruses were shown to cause “nasoencephalopathy” when injected intranasally in mice with subsequent spread to the CNS through the olfactory nerve?⁷ Maybe we shouldn’t be too surprised that sense of smell is impaired in some Covid-19 patients. If we could only stop the virus at the nose!

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References

1. Mao L, Wang M, Chen S, et al. Neurological manifestations of hospitalized patients with COVID-19 in Wuhan, China: a retrospective case series study. https://www.medrxiv.org/content/10.1101/2020.02.22.20026500v1
2. Wu Y, Xu X, Chen Z, et al. Nervous system involvement after infection with COVID-19 and other coronaviruses. Brain, Behavior, and Immunity 2020, March 30. https://www.sciencedirect.com/science/article/pii/S0889159120303573
3. Xiang et al. 2020. First case of 2019 novel Coronavirus disease with encephalitis. ChinaXiv, T202003 (2020), p. 00015 (obtained from reference 2).
4. Poyiadji N, Shain G, Noujaim D, et al. COVID-19-associated acute hemorrhagic necrotizing encephalopathy: CT and MRI features. Radiology 2020 https://pubs.rsna.org/doi/10.1148/radiol.2020201187
5. Filatov A, Sharma P, Hindi F, et al. Neurological complications of coronavirus (COVID-19): encephalopathy. Cureus 12(3): e7352. DOI 10.7759/cureus.7352 https://www.cureus.com/articles/29414-neurological-complications-of-coronavirus-disease-covid-19-encephalopathy
6. Talan J. COVID-19: Neurologists in Italy to Colleagues in US: Look for poorly-defined neurologic conditions in patients with the Coronavirus. Neurology Today 2020, March 27. https://journals.lww.com/neurotodayonline/blog/breakingnews/pages/post.aspx?PostID=920
7. Perlman S, Jacobsen G, Afifi A. Spread of a neurotropic murine Coronavirus into the CNS via the trigeminal and olfactory nerves. Virology 1989;170:556-560 https://www.sciencedirect.com/science/article/pii/0042682289904467

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