Histopathologic changes in lung tissue after Covid-19 pneumonia

ABSTRACT

Current knowledge of histopathological changes in Covid-19 pneumonia is mainly based on autopsy findings. There are few data on dynamics of lung lesions in vivo after acute phase of disease. The aim of this study was to determine histopathologic changes during the long/post-Covid stage in patients who had suffered from moderate to severe Covid-19 pneumonia. Bronchoscopy with transbronchial lung biopsy was performed in patients with HRCT lesions involving >40% of lung parenchyma, at least 4 weeks after discharge. Additional criteria were restrictive pattern in lung function tests and signed informed consent. Histopathologic analyses were performed using H&E, MSB, MOVAT, TTF1, CD34 and CD68 staining. Research was approved by the Hospital Ethical Committee. Among 26 patients that met inclusion criteria, adequate biopsy samples were obtained from 24. The mean time from the onset of disease to biopsy was 13 weeks. We found 4 histopathologic patterns diffuse alveolar damage-DAD with vascular abnormalities, nonspecific interstitial inflammation, organizing pneumonia and interstitial fibrosis in 11, 9, 2 and 2 patients, respectively. Vascular abnormalities included capillary thrombi, dilated venules and dissection of small pulmonary arteries. Given the duration of disease, DAD and vascular abnormalities were detected up to the 12 week from the onset of symptoms. All patients biopsied after 12th weeks had some degree of tissue inflammation without vascular changes. Our findings show rather slow recovery of lung tissue after Covid-19 pneumonia. Long lasting DAD with vascular abnormalities may explain prolonged dyspnea and exercise intolerance and should be taken into consideration when planning further rehabilitation.