Macrophage Activation Syndrome Associated with Adult-onset Still's Disease Successfully Treated with Plasma Exchange and Canakinumab.

We herein describe the case of a 20-year-old Japanese woman with adult-onset Still's disease (AOSD) complicated by macrophage activation syndrome (MAS). Despite the administration of prednisolone and tocilizumab, MAS developed with hyperferritinemia, thrombocytopenia, hypertriglyceridemia, and liver dysfunction. Steroid pulse therapy, cyclosporine A, and plasma exchange (PE) improved the patient's condition. However, diabetes hinders glycemic control under high-dose steroids. Subcutaneous canakinumab (300 mg/month) was initiated, thus enabling rapid prednisolone tapering to 10 mg within one month without relapse. This case highlights that PE followed by canakinumab is a potentially effective strategy for treating severe AOSD with MAS, particularly when minimizing steroid exposure is critical.