Macrophage activation syndrome (MAS)

Macrophage activation syndrome (MAS)

Macrophage activation syndrome is a life-threatening (20% mortality) secondary (reactive) hemophagocytic syndrome occurring in 12% to 19% of AOSD patients. The pathophysiology involves dysregulation of T lymphocytes and excessive production of cytokines resulting in abnormal proliferation of macrophages and a consumptive coagulopathy.

MAS may mimic a flare of AOSD with high persistent fever (not quotidian), hepatosplenomegaly, and an extremely high ferritin (often >10,000 ng/mL) but typically do not manifest arthritis or rash. In addition, unlike AOSD, they have rapidly progressive cytopenias (≥two of three cell lines) due to phagocytosis of hematopoietic cells by macrophages in the bone marrow and reticuloendothelial system. In addition, they develop liver injury (elevated aminotransferases), fasting hypertriglyceridemia (>180 mg/dL), and a consumptive coagulopathy (DIC with elevated prothrombin time/partial thromboplastin time) causing a low fibrinogen level resulting in a low sedimentation rate. Soluble IL-2 receptor (CD25) levels are extremely elevated. Diagnosis is confirmed by a bone marrow aspirate showing hemophagocytosis by macrophages. Hemophagocytosis may also be seen in lymph node, liver, or spleen biopsies. Therapy includes high-dose corticosteroids. Up to 50% may not respond and will require a second-line agent including cyclosporine, etoposide, or biologics (IL-1 inhibitors or TNF inhibitors). Treatments with immunosuppressants (methotrexate, azathioprine, mycophenolate mofetil), and/or IVIG have been described. All patients should be screened by polymerase chain reaction for an active Epstein–Barr or other viral (CMV, parvo) infection which can initiate MAS.


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