Lung long distance: histopathological changes in lung tissue after COVID-19 pneumonia.

Aim: To investigate histopathological changes in the lung tissue of long-COVID patients.

Methods: In this cross-sectional study, transbronchial lung biopsy was performed in long-COVID patients with persisting symptoms and radiological abnormalities. Histopathologic analyses were performed by using hematoxylin-eosin, Martius, Scarlet and Blue, Movat's, thyroid transcription factor 1, CD34, and CD68 staining.

Results: Adequate biopsy samples were obtained from 29/32 patients. The median (Q1-Q3) time from disease onset to biopsy was 13 (9-20) weeks. We observed several histopathologic patterns: DAD with vascular abnormalities (VA) (n=8); VA with inflammatory pattern (n=4); inflammatory pattern (n=13), and fibrotic pattern (n=4). VA included capillary thrombi, dilated venules, and dissection of small pulmonary arteries. DAD with VA was detected up to the 9th week from the onset of disease; inflammatory pattern from the 8th to 28th week (4 patients with this pattern biopsied in the 11th-13th week had accompanying VA); and a predominantly fibrotic pattern was found at weeks 8, 10, 48, and 49.

Conclusion: Our study observed a slow recovery of lung tissue with long-lasting DAD and VA, likely followed by interstitial inflammation or focal fibrosis. These findings might be the underlying cause of the slow recovery of long-COVID patients.