ABSTRACT
Background: Lung transplantation has been performed as a life-saving treatment in a small number of post-acute COVID- 19 patients who develop severe pulmonary insufficiency. We report a detailed clinicopathologic analysis of 7 such patients that underwent bilateral orthotopic lung transplantation at our institution. Design: The time interval between initial diagnosis of Covid-19 infection and lung transplantation, other clinical findings, and imaging features of the 7 patients were reviewed. The pathologic findings in the 14 explants were assessed and histologic abnormalities were classified into parenchymal, airway and vascular changes. The extent (1+-to 4+ based on # of slides with the abnormality) and severity (mild, moderate, marked) of histologic abnormalities were recorded. Results: Patients ranged in age from 34 to 55 years old and were transplanted at 10.4 to 24 weeks after initial diagnosis of Covid- 19 (median 16 weeks). Six of these patients had been previously treated with ECMO for 82-145 days. Other clinical and imaging features are summarized in Table 1. All 14 explants showed diffuse marked interstitial fibrosis with a nonspecific interstitial pneumonia (NSIP) pattern. Other pathologic changes included extensive alveolar hemosiderosis (n=7 patients);prominent peribronchial metaplasia (n=7);focal multinucleated giant cells in either the parenchyma, vascular wall or peribronchiolar location (n=6);focal thrombosis involving medium to large vessels (n=4) and lung cysts associated with delicate calcifications and multinucleated giant cells (n=1). No diffuse alveolar damage changes (DAD) or vasculitis were identified. Conclusions: Lung explants from patients with post-acute COVID-19 syndrome show severe NSIP pattern of fibrosis and other pathologic changes that do not resemble the extensive fibrotic changes resulting from organizing phase of DAD or the extensive vascular changes seen in patients dying during the acute or subacute phases of COVID-19 infection. Further studies with lung biopsies are needed to understand the mechanism of fibrosis in post-acute COVID-19 syndrome and identify individuals who are likely to develop severe pulmonary fibrosis requiring lung transplantation.