The Role of Interleukin-18 in the Diagnosis and Monitoring of Hemophagocytic Lymphohistiocytosis/macrophage Activation Syndrome - a Systematic Review

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening, hyperinflammatory disorder, characterized by multiorgan failure, fever and cytopenias. The diagnosis of HLH and its subtype Macrophage Activation Syndrome (MAS) remains a challenge. Interleukin 18 (IL-18) is emerging as a potential biomarker for HLH/MAS but is currently not a part of diagnostic criteria. This systematic review aimed to assess the potential role of IL-18 in the diagnosis and monitoring of HLH and MAS, and was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. PubMed and Embase were searched on 30 January 2020. Studies included all subtypes of HLH and a range of underlying disorders in both children and adults. A total of 14 studies were included. Generally, serum IL-18 was elevated in both primary and secondary HLH (> 1000 pg/ml) compared with other inflammatory conditions and with healthy individuals; thus, serum IL-18 may be able to discriminate between HLH and other inflammatory conditions. Significantly increased IL-18 (> 10 000 pg/ml) was also consistently described in MAS compared with other subtypes of HLH. The ability of IL-18 to distinguish MAS from systemic juvenile idiopathic arthritis (JIA) is less unambiguous, as IL-18 levels > 100 000 pg/ml were described in sJIA patients both with and without MAS. IL-18 may help to differentiate between HLH subtypes and other inflammatory conditions. As HLH and MAS are rare disorders, only few and relatively small studies exist on the subject. Larger, prospective multi-center studies are called for to assess the diagnostic precision of IL-18 for HLH and MAS.