Increased number of pulmonary megakaryocytes in COVID-19 patients with diffuse alveolar damage. An autopsy study with clinical correlation and review of the literature.

Megakaryocytes are normally present in the lung where they play a role in platelet homeostasis. The latter are well known to participate in the pathogenesis of lung damage, particularly in acute lung injury. Although megakaryocytes are usually not mentioned as a characteristic histopathologic finding associated to acute pulmonary injury, a few studies point out that their number is increased in the lungs of patients with diffuse alveolar damage. In this autopsy study we have observed a relevant number of pulmonary megakaryocytes in COVID-19 patients dying with acute respiratory distress syndrome. We have studied pulmonary tissue samples of 18 patients most of which died after prolonged disease and use of mechanical ventilation. Most samples showed fibroproliferative or fibrotic diffuse alveolar damage and an increased number of megakaryocytes. In six, thrombi of the pulmonary microcirculation were seen. We compare our findings with previous published autopsy reports, mainly focusing on the description of megakaryocytes. Our patients showed abnormal coagulation parameters with high levels of fibrinogen, D-dimers and variable thrombocytopenia. Since the lung is considered an active site of megakariopoiesis, a prothrombotic status leading to platelet activation, aggregation and consumption may trigger a compensatory pulmonary response. An increased number of pulmonary megakaryocytes suggests and supports a relation with the thrombotic events so often seen in COVID-19. Regardless of its etiology, future studies of patients dying with acute pulmonary injury should include pulmonary megakaryocytes as a histologic variable of interest.