Defining Causality In Covid-19 And Neurological Disorders

### Introduction\n\nClinicians 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.\n\nNumerous case reports have since emerged and, at the time of writing, published cases include encephalopathy,3 encephalitis,4 Guillain-Barre 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 \n\nWhether 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.\n\n### Defining causality\n\nIt 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 …