Before the latest coronavirus arrived, the world had already seen 6 coronaviruses. Not all of them led to major epidemics. In fact, only two of the previous coronviruses caused major epidemics: One was the severe acute respiratory syndrome (SARS) and another was Middle East respiratory syndrome (MERS).
Severe acute respiratory syndrome (SARS) was caused by SARS-CoV in 2002–03, while Middle East respiratory syndrome (MERS) was caused by MERS-CoV in 2012.
Both the innocuous and the dangerous coronavirus inlcudng the latest SARS-CoV-2 have been associated with occasional disease of the CNS and peripheral nervous system (PNS).
According to a study published in the Lancet, neurological complications are rare in SARS, MERS, and COVID-19, but the scale of the current pandemic means that even a small proportion could build up to a large number of cases.
The study has identified clinical features of COVID-19-associated neurological disease.
“As the COVID-19 pandemic progresses, reports of neurological manifestations are increasing; to date, 901 patients have been reported. These manifestations can be considered as direct effects of the virus on the nervous system, para-infectious or post-infectious immune-mediated disease, and neurological complications of the systemic effects of COVID-19”, says the study.
In one national registry of 125 patients with COVID-19 and neurological or psychiatric disease reported over a 3-week period,25 39 (31%) patients had altered mental status, which included 16 (13%) with encephalopathy (of whom seven [6%] had encephalitis), and 23 (18%) with a neuropsychiatric diagnosis, including ten (8%) with psychosis, six (5%) with neurocognitive (dementia-like) syndrome, and four (3%) with an affective disorder. Notably, 77 (62%) patients had a cerebrovascular event: 57 (46%) ischaemic strokes, nine (7%) intracerebral haemorrhages, one (<1%) CNS vasculitis, and ten (8%) other cerebrovascular events.
Anosmia and ageusia are common, and can occur in the absence of other clinical features. Unexpectedly, acute cerebrovascular disease is also emerging as an important complication, with cohort studies reporting stroke in 2–6% of patients hospitalised with COVID-19. So far, 96 patients with stroke have been described, who frequently had vascular events in the context of a pro-inflammatory hypercoagulable state with elevated C-reactive protein, D-dimer, and ferritin.
Careful clinical, diagnostic, and epidemiological studies are needed to help define the manifestations and burden of neurological disease caused by SARS-CoV-2. Precise case definitions must be used to distinguish non-specific complications of severe disease (eg, hypoxic encephalopathy and critical care neuropathy) from those caused directly or indirectly by the virus, including infectious, para-infectious, and post-infectious encephalitis, hypercoagulable states leading to stroke, and acute neuropathies such as Guillain-Barré syndrome. Recognition of neurological disease associated with SARS-CoV-2 in patients whose respiratory infection is mild or asymptomatic might prove challenging, especially if the primary COVID-19 illness occurred weeks earlier.