Although, Covid-19 has been reported to be associated with central as well as peripheral nervous system impairment, deficits involving CNS fairly outnumber PNS with impaired consciousness seen in approximately 17% of admitted Covid-19 patients [3]. Possible mechanism by which Covid-19 affects nervous system is still under study, but few hypotheses include direct damage to receptors, cytokine related injury, retrograde travel along the nerve fibres and immune mediated. Mechanism of encephalitis in patients with Covid-19 is not totally clear, but likely possibilities include inflammatory injury and direct viral infection [6]. A number of case series have shown association of CNS manifestations with severe Covid-19 infection and elevated inflammatory markers like D-Dimer and interleukin-6 (IL-6) [3,7]. Our case report supports the hypotheses of association between CNS manifestation and severe form of Covid-19 infection and raised inflammatory markers.
AHL is one of the aggressive variants of acute disseminated encephalomyelitis (ADEM), which is found in less than 2% of patients with ADEM and is most often triggered by an upper respiratory tract infection [5]. A few clinical and radiological clues help in differentiating ADEM from its rare and more aggressive variant. Although, AHL and ADEM share a common aetiology i.e. autoimmune process directed against CNS myelin, clinically, hyperacute onset, rapid progression and high mortality seen in AHL helps in differentiating it from ADEM [8]. Similarly, both ADEM and AHL on imaging are characterised by perivenular demyelination and inflammation predominantly involving white matter, but asymmetric or symmetric subcortical white matter involvement of posterior fronto-parietal lobes with relative sparing of the cortex is characteristic of AHL. Involvement of Basal ganglia which is quite common in ADEM is relatively rare in AHL and thus, helps in differentiating the two [9]. Our patient had an almost sudden onset and a very rapidly progressive downhill course associated with MRI showing bilateral asymmetric confluent FLAIR hyperintensities in subcortical white matter involving the posterior fronto-parietal lobes and splenium of corpus callosum suggestive of demyelination and inflammation, with sparing of basal ganglia and cortex with punctate haemorrhages noted in the splenium. FLAIR hyperintensity in cervical cord was suggestive of myelitis. Thus, clinico-radiological manifestation of our patient was suggestive of AHL and although, it has a poor prognosis, our patient had a good neurological response to steroids but unfortunately, severe respiratory dysfunction due to Covid-19 led to his mortality. Other conditions which share the common imaging findings are: progreesive multifocal leukoencephalopathy (PML), vasculitis and lymphoma. Hyperacute onset and rapidly progressive course help in differentiating the above conditions from AHL, as all of these have a subacute to indolent course [9]. Various treatments which have been described to be effective in AHL include high dose steroids, IV Immunoglobulins, plasmapheresis and cyclophosphamide [4].