Cross-sectional case-control studies (Blue)
In this research letter, the authors evaluated brain tissue from autopsies of patients with nucleic acid–proven severe acute respiratory syndrome coronavirus 2 infection and confirmed pulmonary pathology. The authors assessed the brains from the first 5 such cases at Johns Hopkins University; for 2 of these, only fragments of brain were available. Cases from Massachusetts General Brigham were randomly selected from autopsies of individuals with COVID-19 performed between April 14 and May 15, 2020, and free of infarcts. COVID-19–negative cases were chosen based on comparable patient age and the presence of hypoxic-ischaemic changes in brain. Brains were fixed in neutral buffered formalin 10% for 2 weeks, then grossly examined and sectioned for microscopic assessment. In 5 cases, in cortical capillaries, the authors identified large cell nuclei morphologically consistent with megakaryocytes. To further characterise these cells, they performed immunohistochemistry for CD61 and CD42b, markers of platelets and megakaryocytes. CD61 labels these cells, as does CD42b, confirming their megakaryocyte identity. The cells were distinct from platelet clusters, which were found in post-mortem intravascular precipitates. Evaluation of the cortex of two patients who tested negative for COVID-19 who had hypoxic brain changes demonstrated no megakaryocytes on CD61.