Comparing COVID-19-linked neurological complications with other viral infections

There are increasing reports of multi-system involvement in coronavirus disease 2019 (COVID-19). Among these, cerebrovascular diseases (CVD) in COVID patients have been highlighted to be associated with varied features and prognosis. COVID-19 may possess the similar mechanism and clinical characteristics as SARS, as the viruses causing them are under the same category and share highly homological genetic sequence. Influenza H1N1 and COVID-19 are comparable in terms of outbreak size as Influenza H1N1 also bring about global pandemic. However, to date, a detailed systematic comparison of neurological complications among COVID-19, SARS-CoV-1 and Influenza H1N1 infections has not been carried out.

To address this gap in knowledge, we compared the frequency, presentation and prognosis of neurological complications in COVID-19 with SARS and Influenza H1N1 infection (Tables 1, 2). This may provide further mechanistic insights into potential differences between COVID-19 and other viral infections.

Table 1 Severe neurological symptoms among different viral infections

Table 2 Cerebrovascular disease among different COVID-19 reports

We searched PubMed from January, 2020 to June, 2020. The following key words were included: “COVID-19”, “SARS”, “influenza”, “cerebrovascular disease”, “neurological symptoms”, “neurological manifestations”. Two review authors (EK-T, XD) independently reviewed the included studies and extracted study characteristics.

About 3% of COVID-19 patients reported acute CVD in a study from Wuhan [1], comparable to the reported frequency of 2.42% for SARS reported in Singapore [2]. Neurologic manifestations occurred both early and late stage in the course of the COVID-19 [3], with more clinical variability than SARS and H1N1 infections. The most common severe neurologic manifestations in COVID-19 patients included acute CVD, impaired consciousness, and skeletal muscle injury, which appeared slightly higher than SARS and H1N1 patients [1, 2, 4, 5]. Acute symptomatic seizures or status epilepticus were not seen commonly in COVID-19 patients [6]. More children with H1N1 than adults suffered neurologic injury with poor outcome [7], whereas paediatric patients with COVID-19 were more likely to have better outcome than adults [8] (Table 1).

For CVD in COVID-19, we noticed that a number of them were relatively young (less than 50 years and of male gender) (Table 2). There was no consistent pattern to the types of strokes, with reports of involvement in small, medium or large vessels [3, 9] (Table 2). The blockages of these vessels led to infarcts and in some cases frank bleeding. The prognosis depended on the severity of the strokes at presentations and associated complications. Not surprisingly, vascular risk factors such as hyperlipidaemia, diabetes and hypertension were present especially in the older group of patients [10]. These risk factors were not different from the common stroke patients seen during non-COVID-19 period. Several patients in one series [3] have been reported to have a positive lupus anticoagulant, which may have predisposed them to the disease. However, it is not clear if these patients were more susceptible to COVID-19 or if there was a complex interplay of the factors involved. It is possible that proinflammatory cytokines contributed to the blockage of the vessels [3]. For those stroke patients who were disabled, long term data on the final recovery outcomes were still not available.

The infection of SARS‐CoV can affect brains, especially the brainstem mainly mediated by a cellular receptor angiotensin‐converting enzyme 2 (ACE2) [11], which can be expressed in human airway epithelia, lung parenchyma, vascular endothelia. The similarity of severe neurological manifestations in COVID-19 and in SARS patients indicate that ACE2 may also play a role in the underlying mechanism. In addition, the respiratory failure in COVID-19 patients may result from the neuroinvasive potential of SARS‐CoV2 [11]. Different from the possible mechanisms of SARS-CoV-1 and SARS-CoV-2 infections, H1N1 infection might be due to direct infection, hypoxia and metabolite dysfunction [12].

To summarise, based on current data, the frequency of CVD in COVID-19 appeared slightly more than SARS and H1N1 patients. COVID-19 had more variability than SARS and H1N1 patients in terms of the onset of neurologic manifestations. Longitudinal studies to further clarify the chronic neurological burden could be particularly useful to stratify COVID-19 patients and guide the medical recourse allocation. It could be particularly useful to guide strategic planning for current and future pandemics. Functional studies to decipher the pathophysiologic mechanism, in particular the role of the COVID-19 in vessel wall inflammation, blockage and secondary cytokine response will be warranted.