COVID-19 Associated Hemophagocytic Lymphohistiocytosis and Coagulopathy: Targeting the Duumvirate.

Context: Preliminary data on coexistence of secondary hemophagocytic lymphohistiocytosis syndrome (HLH) and disseminated intravascular coagulation (DIC) in critically ill children with novel coronavirus disease (COVID-19) are emerging. Herein, we summarize the available literature and fill-in the gaps in this regard.

Evidence Acquisition: We have performed a literature search for articles in PubMed, EMBASE and Google Scholar databases till May 12, 2020, with following keywords: "COVID-19", "SARS-CoV-2", "HLH", "HScore", "coagulopathy", "D-dimer", "cytokine storm", "children" and "pediatrics" with interposition of Boolean operator "AND".

Results: Children presenting with moderate-severe COVID-19 and Kawasaki disease shock-like syndrome exhibit peripheral blood picture analogous to HLH. HScore, a validated tool to diagnose HLH, has been suggested to screen severe COVID-19 patients for cytokine storm. However, HScore faces certain limitations in this scenario. It may be more pragmatic to use 'high D-dimer' (> 3 µg/mL) instead of 'low fibrinogen' to facilitate early detection of cytokine storm. COVID-19 associated coagulopathy resembles hypercoagulable form of DIC with bleeding being rarely reported. Although the International Society on Thrombosis and Haemostasis (ISTH) interim guidance recommends low molecular weight heparin in all hospitalized patients, data is lacking in population below 14 years of age. However, in the presence of life-threatening thromboembolic event or symptomatic acro-ischemia, unfractionated heparin (UFH) should be used with caution.

Conclusions: HScore can be used as a complement to clinical decision for initiating immunosuppression. Children with moderate-to-severe COVID-19, especially those with documented thrombocytopenia or chilblains, should be regularly monitored for coagulopathy.