Yang and Ying of ruxolitinib administration for macrophage activation syndrome complicated by systemic juvenile idiopathic arthritis

DEAR EDITOR, Haemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition characterized by cytokine storm and multiple organ failure resulting from excessive immune activation.Macrophage activation syndrome (MAS) is a secondary HLH associated with rheumatic diseases.Ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor, has shown promising results for disease control of HLH/MAS [1][2][3][4].However, the optimal oral dosage and duration have not been established yet.Furthermore, ruxolitinib has concerning side effects, including increased risk for infections.Here, we report a case of MAS associated with systemic JIA (s-JIA) successfully treated with ruxolitinib, but it was complicated by EBV-associated HLH (EBV-HLH) and agranulocytosis.A 3-year-old girl with fever lasting for 8 days, rash and arthralgia was referred to us.She was diagnosed with incomplete Kawasaki disease, which was treated with intravenous immunoglobulin, methylprednisolone pulse therapy (MPT; 30 mg/kg/day, 3 days) and CsA.Physical examination revealed 20.3 kg of body weight, skin rash, redness of lips, aphthous stomatitis and hepatosplenomegaly.Laboratory data revealed hyperferritinaemia, elevated aspartate aminotransferase and coagulopathy (Supplementary Table S1, available at Rheumatology online).Serum cytokine levels, including IL-18, were significantly elevated (Fig. 1A).She was diagnosed with MAS associated with s-JIA.Additional two MPT courses in combination with dexamethasone palmitate and CsA led to MAS remission (Fig. 1B).However, herRheumatology key message Ruxolitinib is effective for MAS but its complications, including infection and neutropenia, should be addressed.