Thrombosis is one of the four dominant interrelated pathological processes in severe COVID-19 along with diffuse alveolar damage (DAD), haemophagocytosis, and immune cell depletion, an autopsy series confirms.

Researchers from the Imperial College London who conducted post-mortems on ten COVID-19 patients found thrombi in the lungs of eight patients, the heart of five patients and the kidneys of four patients.

The team were unable to investigate thrombosis in the tenth patient.

“Thrombotic features were universal among patients who underwent full autopsies (all nine patients had thrombi in at least one major organ) and have been noted to be prominent in other COVID-19 autopsy series,” the study authors wrote in their series published in The Lancet Microbe.

“Whether thrombosis in COVID-19 is more common than in other causes of DAD remains uncertain; however, our data support thrombosis as being a striking feature in these patients,” they said.

The researchers also documented lymphocyte depletion, particularly CD8-positive T cells, in the spleen and the lymph nodes as well as haemophagocytosis.

Unexpected findings from the autopsy series included pancreatitis, pericarditis, adrenal micro-infarction, secondary disseminated mucormycosis, and brain microglial activation.

“The evidence of ongoing replication late in disease supports the use of antiviral therapy, even at a point in illness when immunopathology is dominant,” they suggested.

Dr Michael Osborn, Honorary Clinical Senior Lecturer at Imperial College London, Consultant Pathologist at Imperial College Healthcare NHS Trust and co-author of the study, said: “COVID-19 is a new disease and we have only had limited opportunities to comprehensively analyse tissues from patients at autopsy, to better understand what caused a patient’s illness and death for research purposes.

“Our study is the first of its kind in the country to support existing theories from researchers and doctors on the wards that lung injuries, thrombosis and immune cell depletion are the most prominent features in severe cases of COVID-19.  In the patients we looked at, we also saw evidence of kidney injuries and in some cases pancreatitis and these with our other findings will help clinicians develop new strategies to manage patients.”

The team performed full post-mortem examinations and biopsies on ten patients aged 22-97 years at Imperial College Healthcare NHS Trust hospitals during March to June 2020. Seven of the patients were men and four were women.  Six of the patients were from a BAME background and four patients were white.