Inflammatory biomarkers in COVID-19-associated multisystem inflammatory syndrome in children, Kawasaki disease, and macrophage activation syndrome: a cohort study

Abstract

Background: Multisystem inflammatory syndrome in children (MIS-C) is a potentially life-threatening hyperinflammatory syndrome that occurs after primary SARS-CoV-2 infection. The pathogenesis of MIS-C remains undefined, and whether specific inflammatory biomarker patterns can distinguish MIS-C from other hyperinflammatory syndromes, including Kawasaki disease and macrophage activation syndrome (MAS), is unknown. Therefore, we aimed to investigate whether inflammatory biomarkers could be used to distinguish between these conditions.

Methods: We studied a prospective cohort of patients with MIS-C and Kawasaki disease and an established cohort of patients with new-onset systemic juvenile idiopathic arthritis (JIA) and MAS associated with systemic JIA (JIA-MAS), diagnosed according to established guidelines. The study was done at Cincinnati Children's Hospital Medical Center (Cincinnati, OH, USA). Clinical and laboratory features as well as S100A8/A9, S100A12, interleukin (IL)-18, chemokine (C-X-C motif) ligand 9 (CXCL9), and IL-6 concentrations were assessed by ELISA and compared using parametric and non-parametric tests and receiver operating characteristic curve analysis.

Findings: Between April 30, 2019, and Dec 14, 2020, we enrolled 19 patients with MIS-C (median age 9·0 years [IQR 4·5-15·0]; eight [42%] girls and 11 [58%] boys) and nine patients with Kawasaki disease (median age 2·0 years [2·0-4·0]); seven [78%] girls and two [22%] boys). Patients with MIS-C and Kawasaki disease had similar S100 proteins and IL-18 concentrations but patients with MIS-C were distinguished by significantly higher median concentrations of the IFNγ-induced CXCL9 (1730 pg/mL [IQR 604-6300] vs 278 pg/mL [54-477]; p=0·038). Stratifying patients with MIS-C by CXCL9 concentrations (high vs low) revealed differential severity of clinical and laboratory presentation. Compared with patients with MIS-C and low CXCL9 concentrations, more patients with high CXCL9 concentrations had acute kidney injury (six [60%] of ten vs none [0%] of five), altered mental status (four [40%] of ten vs none [0%] of five), shock (nine [90%] of ten vs two [40%] of five), and myocardial dysfunction (five [50%] of ten vs one [20%] of five); these patients also had higher concentrations of systemic inflammatory markers and increased severity of cytopenia and coagulopathy. By contrast, patients with MIS-C and low CXCL9 concentrations resembled patients with Kawasaki disease, including the frequency of coronary involvement. Elevated concentrations of S100A8/A9, S100A12, and IL-18 were also useful in distinguishing systemic JIA from Kawasaki disease with high sensitivity and specificity.

Interpretation: Our findings show MIS-C is distinguishable from Kawasaki disease primarily by elevated CXCL9 concentrations. The stratification of patients with MIS-C by high or low CXCL9 concentrations provides support for MAS-like pathophysiology in patients with severe MIS-C, suggesting new approaches for diagnosis and management.

Funding: Cincinnati Children's Research Foundation, National Institute of Arthritis and Musculoskeletal and Skin Diseases/National Institutes of Health, the Deutsche Forschungsgemeinschaft, and The Jellin Family Foundation.

Figure 1

Comparison of haematology and laboratory results Data are median (IQR). All data are first sets of laboratory tests obtained during admission except for platelets in which (E) shows nadir and (F) shows peak concentrations recorded during admission. Red data points indicate concentrations outside the normal range for the indicated parameter. Participant numbers were as follows unless otherwise noted: n=11 systemic JIA, n=9 systemic JIA-MAS, n=9 Kawasaki disease, and n=19 MIS-C. Data analysed using one-way ANOVA if data were parametric or Kruskal-Wallis if non-parametric and post-hoc multiple comparison correction was made. JIA=juvenile idiopathic arthritis. MAS=macrophage activation syndrome. MIS-C=multisystem inflammatory syndrome in children. *p≤0·05. †p≤0·01. ‡p<0·1.

Figure 2

Comparison of S100A8/A9, S100A12, IL-18, CXCL9, and IL-6 concentrations Data are median (IQR). All data are first sets of laboratory tests obtained during admission. Red data points indicate concentrations outside the normal range for the indicated parameter. Data analysed using one-way ANOVA if data were parametric or Kruskal-Wallis test if non-parametric and post-hoc multiple comparison correction was made. JIA=juvenile idiopathic arthritis. MAS=macrophage activation syndrome. MIS-C=multisystem inflammatory syndrome in children. IL=interleukin. CXCL=chemokine (C-X-C motif) ligand. *p≤0·05. †p≤0·01. ‡p≤0·001. §p≤0·0001.

Figure 3

Diagnostic utility of inflammatory biomarkers for MIS-C, Kawasaki disease, and systemic JIA (A) ROC curves for CXCL9 in differentiating MIS-C versus Kawasaki disease. ROC curves for S100A8/9 (B), S100A12 (C), and IL-18 (D) in differentiating systemic JIA from Kawasaki disease. Sensitivities and specificities for the optimal cutoff values are noted. Red dots represent optimal cutoff points. JIA=juvenile idiopathic arthritis. MAS=macrophage activation syndrome. MIS-C=multisystem inflammatory syndrome in children. ROC=receiver operating characteristic.

Figure 4

Differential CXCL9 concentrations in MIS-C with and without MAS Data are median (IQR). (A) CXCL9 concentrations in patients with MIS-C that did or did not meet MAS classification criteria using only strict criteria (left) and including strict and subclinical MAS (right). CXCL9 concentrations of patients with subclinical MAS are shown with half-filled black circles. Data were analysed using the Mann-Whitney test. (B) ROC curves for CXCL9 differentiating MIS-C without and with MAS using strict 2016 MAS classification criteria. The red dot indicates the optimal cutoff point. (C) One patient with MIS-C underwent bone-marrow biopsy as part of their diagnostic evaluation and the smear shows haemophagocytosis with an ingested lymphocyte and a myeloid precursor in the process of being ingested by a histocyte. (D) ROC curve for CXCL9 differentiating MIS-C without and with strict plus subclinical MAS. The red dot indicates the optimal cutoff point. ROC=receiver operating characteristic. JIA=juvenile idiopathic arthritis. MAS=macrophage activation syndrome. MIS-C=multisystem inflammatory syndrome in children. *p≤0·05. †p≤0·01.