Differentiating Macrophage Activation Syndrome in Systemic Juvenile Idiopathic Arthritis from Other Forms of Hemophagocytic Lymphohistiocytosis

Objectives To identify measures distinguishing macrophage activation syndrome (MAS) in systemic juvenile idiopathic arthritis (sJIA) from familial hemophagocytic lymphohistiocytosis (FHL) and virus-associated hemophagocytic lymphohistiocytosis (VA-HLH) and to define appropriate cutoff values. To evaluate suggested dynamic measures differentiating MAS in patients with sJIA from sJIA flares. Study design In a cohort of patients referred for evaluation of hemophagocytic lymphohistiocytosis, we identified 27 patients with sJIA and MAS (MAS/sJIA) fulfilling the criteria of the proposed preliminary diagnostic guideline for the diagnosis of MAS in sJIA. Ten measures at diagnosis were compared between the MAS/sJIA group and 90 patients with FHL and 42 patients with VA-HLH, and cutoff values were determined. In addition, 5 measures were analyzed for significant change from before MAS until MAS diagnosis. Results Neutrophil count and C-reactive protein were significantly higher in patients with MAS/sJIA compared with patients with FHL and patients with VA-HLH, with 1.8 x 10(9)/L neutrophils (sensitivity 85%, specificity 83%) and 90 mg/L C-reactive protein (74%, 89%) as cutoff values. Soluble CD25 <7900 U/L (79%, 76%) indicated MAS/sJIA rather than FHL/VA-HLH. Platelet (-59%) and white blood cell count (-46%) displayed a significant decrease, and neutrophil count (-35%) and fibrinogen (-28%) showed a trend during the development of MAS. However, a substantial portion of patients had values at diagnosis of MAS within or above the normal range for white blood cells (84%), neutrophils (77%), platelets (26%), and fibrinogen (71%). Conclusion Readily available measures can rapidly differentiate between MAS/sJIA and FHL/VA-HLH. The findings substantiate that a decline of measures may facilitate the distinction of MAS from flares of sJIA.