Abstract Details Title Coronavirus 2019: clinical and neuropathological aspects Topic Autoimmune Neurology Presentation(s) S3 - Autoimmune Neurology 1: Mechanisms of Disease, Clinical Practice (1:00 PM-1:12 PM) Poster/Presentation Number 001 Background Analysis of 50 cases of COVID-19 with available neuropathology revealed three CNS findings. First, hypoxia-ischemia does not account for all relevant neuropathological features. Second, elevated levels of circulating cytokines suggest activation of post-infectious immunity indicative of a cytokine storm, with increased hypercoagulability leading to a risk for thrombotic and hemorrhagic parenchymal tissue infarction. Third, a minority of cases have acute demyelinating encephalomyelitis-(ADEM) like features or indolent brainstem encephalitis. Such cases may present with early altered sensorium and brainstem signs. Fourth, SARS-CoV-2 staining could not be confirmed due to paucity of available tissue specimens. Objective To describe the clinicopathological correlations of 141 confirmed postmortem cases of coronavirus disease 2019 (COVID-19) due to severe acute respiratory syndrome-coronavirus -2 (SARS-CoV-2). Design/Methods Ninety-four additional cases with available postmortem CNS neuropathology showed four additional findings. Results First, positive SARS-CoV-2 genome by PCR testing is present in brain tissues especially in olfactory bulb neurons and glial cells lending support to a route of entry into the CNS and the importance of early anosmia. Second, SARS-CoV-2-positive neurons appear to be TUNEL positive and caspase-positive, displaying reversible pT231 Tau localization in some cell soma that may be highly neurotoxic and a driver of tauopathy. Third, expression of ACE2 in oligodendrocytes is associated with viral entry, while TMPRSS2 and TMPRSS4 staining is implicated in pruning of viral-decorating spikes. Fourth, meningeal and interstitial brainstem inflammation by cytotoxic T-cells coincides with the localization of SARS-CoV-2 viral proteins in cranial nerves and interstitial areas of lower brainstem encephalitis. The detection of brain microglial activation and sparse perivascular and leptomeningeal T-cell infiltrates correlates with critical illness encephalopathy. Conclusions Genetic diversity, recombination, and viral mutation carries the foreseeable risk of continued fatality due to the direct and indirect effects of SARS-CoV-2 that include inflammatory vasculopathy, encephalitis, silent infarctions, and critical illness encephalopathy. Authors/Disclosures David S. Younger, MD, DrPH, MPH, MS PRESENTER Dr. Younger has nothing to disclose.