This article was originally published here
Hum Pathol. 2021 Jul 14:S0046-8177(21)00122-2. doi: 10.1016/j.humpath.2021.06.008. Online ahead of print.
OBJECTIVES: Severe COVID-19 results in a glucocorticoid responsive form of acute respiratory distress (ARDS)/diffuse alveolar damage (DAD). Herein we compare the immunopathology of lung tissue procured at autopsy in patients dying of SARS-CoV-2 with those dying of DAD prior to the COVID-19 pandemic.
METHODS: Autopsy gross and microscopic features stratified by duration of illness in twelve patients who tested positive for SARS-CoV-2 viral RNA as well as seven patients dying of DAD prior to the COVID-19 pandemic were evaluated with multiplex (5-plex: CD4, CD8, CD68, CD20, AE1/AE3) and SARS-CoV immunohistochemistry to characterize the immunopathologic stages of DAD.
RESULTS: We observed a distinctive pseudopalisaded histiocytic hyperplasia interposed between the exudative and proliferative phase of COVID-19 associated DAD which was most pronounced at the fourth week from symptom onset. Pulmonary macrothrombi were seen predominantly in cases with pseudopalisaded histiocytic hyperplasia and/or proliferative phase DAD. Neither pseudopalisaded histiocytic hyperplasia nor pulmonary macrothrombi were seen in non-COVID-19 DAD cases, whereas microthrombi were common in DAD regardless of etiology.
CONCLUSION: The inflammatory pattern of pseudopalisaded histiocytic hyperplasia may represent the distinctive immunopathology associated with the dexamethasone responsive form of DAD seen in severe COVID-19.