Bone marrow haemophagocytosis designate severe SARS-CoV-2 infections.

AIMS: Haemophagocytosis in the bone marrow of patients who have succumbed to COVID-19 has not been widely studied. The aim of the present study was to perform morphological analyses and morphometry of haemophagocytosis in bone marrow of patients with severe COVID-19 and to correlate the findings to the clinical course of the disease. METHODS AND RESULTS: In the single-centre study at the University Hospital Jena bone marrow specimens of 15 deceased patients with severe course of COVID-19 were sampled from vertebral column during autopsy. Slides of bone marrow were stained with routine stains or immunohistochemistry and further examined for haemophagocytosis using light microscopy. To substantiate morphological findings additional slides were stained against CD163 and morphometry was performed. In all bone marrow samples, a relative increase in cellularity was found. Haemophagocytes with erythrophagocytosis were detectable in 67% of the deceased patients. In tissues with low number of haemophagocytes or ill-defined haemophagocytes, an increase in iron deposits was frequently seen. Next, morphological findings were correlated with several important clinical data and the H-Score was calculated to posthumously confirm the diagnosis secondary haemophagocytic lymphohistiocytosis (sHLH). Median duration of disease and hospitalisation time were shorter in patients with haemophagocytosis (n=10) compared to patients without haemophagocytosis (n=5). In addition, patients with haemophagocytes showed increased inflammatory parameters two to five days prior to death compared to patients without haemophagocytes. CONCLUSIONS: Haemophagocytosis is a common finding in the bone marrow of deceased with severe COVID-19 and may designate fatal SARS-CoV-2 infections.