Hemophagocytic syndrome and inflammatory myopathy with abundant macrophages in a patient with adult-onset Still's disease.

We herein describe a 71-year-old woman with adult-onset Still's disease (AOSD) who developed fever, myalgia, and pancytopenia. The bone marrow aspiration and muscle biopsy revealed hemophagocytic syndrome (HPS) and inflammatory myopathy with abundant macrophages (IMAM). Immunostained specimens were positive for expression of retinoic acid-inducible gene-I (RIG-I), which recognizes viral RNA in infiltrated mononuclear cells as well as muscle tissues. These findings suggest that RIG-I may be involved in induction of HPS and IMAM in AOSD.