... been reported in association with many rheumatic diseases, most commonly in systemic juvenile rheumatoid arthritis (sJRA). Clinically, MAS is similar to hemophagocytic lymphohistiocytosis (HLH), ... joints involved), polyarticular(five or more joints), and systemic. The systemic onset form, with its markedly febrile presentation, is certainly the mostdistinct clinical subtype of the disease. ... (or histiocytes) actively phagocytosing hemat-opoietic elements. Although MAS has been increasinglyrecognized in association with almost any rheumatic dis-ease, it is by far most common in the...