Introduction
Clinicians are increasingly recognising neurological presentations occur in some patients.1 A case series from Wuhan described associated neurological syndromes (eg, ‘dizziness’ and ‘impaired consciousness’), but with little detail regarding symptomatology, and cerebrospinal fluid (CSF) and neuroimaging findings.2 The extent to which these disorders were caused by the virus per se, rather than being complications of critical illness, unmasking of degenerative disease, or iatrogenic effects of repurposed medications is not clear.
Numerous case reports have since emerged and, at the time of writing, published cases include encephalopathy,3 encephalitis,4 Guillain-Barré syndrome (GBS)5 and stroke.6 In most of these cases, the virus has been identified in respiratory samples, and in a small number in CSF. So far, the reporting of clinical features has been extremely variable, for example, several cases have claimed to report encephalitis without clear evidence of central nervous system (CNS) inflammation, which would not meet established definitions of the disease.7
Whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) is associated with neurological manifestations is of critical importance as this may result in substantial morbidity and mortality.
Defining causality
It is crucial that neurologists and neuropsychiatrists apply a systematic strategy to determine whether there is evidence that SARS-CoV2 is causing these manifestations, whether they are a consequence of severe systemic disease alone, or simply coincidence. In 1965, Hill proposed criteria on which to build an argument for disease causation, which can be applied to COVID-19.8
What is the strength of the association?
So far, it appears fairly weak . >2.5 million people have been infected with SARS-CoV2 and to date (to the authors’ knowledge) there have been only 93 published cases of neurological manifestations (about 5/100 000). However, reported cases are an underestimate of the real incidence, and this underscores the need for proper epidemiological study.