Severe COVID-19-associated hyperinflammatory syndrome versus classic hemophagocytic lymphohistiocytosis: similarities, differences, and the way forward

The hyperinflammatory immune response in severe COVID-19 infection shares features with secondary hemophagocytic lymphohistiocytosis (sHLH) in the form of fever, cytopenia, elevated inflammatory markers, and high mortality. There are contrasting opinions regarding utility of HLH 2004 or HScore in the diagnosis of severe COVID-19-related hyperinflammatory syndrome (COVID-HIS). This was a retrospective study of 47 patients of severe COVID-19 infection, suspected to have COVID-HIS and 22 patients of sHLH to other illnesses, to evaluate the diagnostic utility and limitations of HLH 2004 and/or HScore in context to COVID-HIS and to also evaluate the utility of Temple criteria for predicting severity and outcome in COVID-HIS. Clinical findings, hematological, and biochemical parameters along with the predictor of mortality were compared between two groups. Only 6.4% (3/47) of cases fulfilled ≥5/8 HLH 2004 criteria and only 40.52% (19/47) of patients showed HScore >169 in COVID-HIS group. 65.9% (31/47) satisfied the Temple criteria in COVID-HIS as compared with 40.9% (9/22) in the non-COVID group (p = 0.04). Serum ferritin (p = 0.02), lactate dehydrogenase (p = 0.02), direct bilirubin (p = 0.02), and C-reactive protein (p = 0.03) were associated with mortality in COVID-HIS. Both HScore and HLH-2004 criteria perform poorly for identifying COVID-HIS. Presence of bone marrow hemophagocytosis may help to identify about one-third of COVID-HIS missed by the Temple Criteria.