Macrophage activation syndrome (MAS) is a severe and potentially fatal immune phenomenon characterized by overactivation and proliferation of macrophages and T cells. It is closely related to hemophagocytic lymphohistiocytosis (HLH), a similar diagnosis that may occur as a result of genetic factors or certain malignancies. HLH and MAS are thought to exist along a spectrum, and MAS has been described as a type of secondary HLH that occurs in patients with an underlying rheumatologic disorder. Although most closely associated with systemic-onset juvenile idiopathic arthritis (SoJIA), MAS is also associated with numerous other rheumatologic diseases, including systemic lupus erythematosus and KD.
Patients with MAS have characteristic laboratory findings, including low cell counts, ESR, and fibrinogen levels, along with elevated liver function test results, coagulation test findings, and ferritin levels. Clinical manifestations include bleeding, hepatosplenomegaly, unremitting fevers and rash, lethargy, seizures, coma, and death.
Criteria for MAS complicating SoJIA state that a febrile patient with known or suspected SoJIA is classified as having MAS if they have a ferritin level ≥ 684 ng/L, in addition to two of the following:
Platelet count ≤ 181 × 109/L AST level > 48 U/L Triglyceride level > 156 mg/dL Fibrinogen level ≤ 360 mg/dL
A diagnostic tool has also been developed to distinguish MAS from primary HLH. Patients with primary HLH tend to be younger (age at onset, ≤ 1.6 years) with more pronounced neutropenia, anemia, and thrombocytopenia; lower fibrinogen level; and a higher likelihood of splenomegaly.
Medscap dec 2019