Ruxolitinib rescued the macrophage activation syndrome in adult-onset Still's disease with delayed hypersensitivity reaction to tocilizumab

Dear Editor, Although tocilizumab (TCZ) has demonstrated high efficacy in the treatment of refractory adult-onset Still’s disease (AOSD), it is associated with numerous adverse events including severe hypersensitivity reactions [1]. On rare occasions, hypersensitivity could occur within hours of TCZ infusion [2]. TCZ could also induce severe delayed hypersensitivity reactions (DHR), days to months after exposure. TCZ-induced DHR has previously been linked to human leucocyte antigens (HLA)-DRB1*15 alleles across ancestries. Typically, DHRs manifest as drug reaction with eosinophilia and systemic symptoms (DRESS) [3]. In this study, we present the case of a 34-year-old Chinese woman who was diagnosed with AOSD according to the Yamaguchi criteria at the age of 31. The clinical symptoms included fever, rash, pharyngalgia and arthralgia accompanied by elevated levels of white blood cells and ferritins [4]. The patient was administered prednisone and methotrexate at a dose of 10 mg per week (later switched to leflunomide 10 mg bid due to inadequate control of arthralgia) as the initial treatment. The disease course in the first year post-diagnosis was uneventful and the prednisone was reduced to a lower dose of 5 mg/day as maintenance. However, the patient experienced sudden worsening of symptoms, which led to the onset of macrophage activation syndrome (MAS; as evidenced by an HScore of 179) [5] accompanied by capillary leak syndrome. Owing to this, TCZ was prescribed at a high dose of 240 mg every 2 weeks for 3 months, which was eventually modified to 480 mg every 4 weeks thereafter. The patient remained in remission for over a year with prednisone gradually tapered to 2.5 mg per day.