macrophage activation syndrome (MAS)

Macrophage Activation Syndrome (also known as Hemophagocytic lymphohistiocytosis (HLH)

• when associated with rheumatic disorders, is a frequently fatal complication of infections, rheumatic disorders, and hematopoietic malignancies
  • often termed a “cytokine storm,” MAS occurs among the rheumatic diseases most typically in Still's disease but also in systemic lupus erythematosus and Kawasaki disease (2)
  • can also accompany infection, malignancy, and inborn errors of immunity (2)
• is a life-threatening condition that is usually diagnosed among febrile hospitalized patients (children and adults) who commonly present with unremitting fever and a shock-like multiorgan dysfunction scenario
• laboratory studies reveal:
  • pancytopenia
  • elevated liver enzymes
  • elevated markers of inflammation (ESR, CRP)
  • hyperferritinemia,
  • features of coagulopathy

• in about 60% of cases, excess hemophagocytosis (macrophages/histiocytes engulfing other hematopoietic cell types) is noted on biopsy specimens from the bone marrow, liver, lymph nodes, and other organs (1)

Reference:

1. Eloseily EM, Cron RQ. Macrophage Activation Syndrome. The Microbiome in Rheumatic Diseases and Infection. 2018 Mar 13:151–82.
2. Nigrovic, PA. Macrophage Activation Syndrome. Arthritis Rheumatol 2025; 77: 367-379