A Case of Macrophage Activation Syndrome During the Treatment of Adult-onset Still's Disease With Tocilizumab.

Macrophage activation syndrome (MAS) is a fatal complication of adult-onset Still's disease (AOSD). Although anti-cytokine agents have been recommended for refractory AOSD or complicated with MAS, MAS cases have been rarely reported during anti-cytokine treatment. Herein, we describe the first AOSD case complicated with MAS during the treatment with tocilizumab in Korea. Two years after tocilizumab maintenance therapy, high fever and hypertransaminasemia recurred. MAS was diagnosed based on hyperferritinemia, elevated soluble IL-2 receptor levels, and the presence of hemophagocytic histiocytes in the bone marrow. However, she had normal white blood cell counts and acute phase reactant levels. High-dose glucocorticoid and anakinra therapies were not effective, but her disease improved with etoposide. This case shows that tocilizumab may not prevent MAS development and can modify clinical features making it challenging to diagnose. Cytotoxic therapy such as etoposide may be required in MAS cases that develop during anti-cytokine therapy.