Macrophage activation syndrome is a severe, potentially life-threatening, complication of several chronic rheumatic diseases of childhood. It occurs most commonly with systemic-onset juvenile idiopathic arthritis (SoJIA). In addition, MAS has been described in association with systemic lupus erythematosus (SLE), Kawasaki disease, and adult-onset Still's disease. It is thought to be closely related and pathophysiologically very similar to reactive (secondary) hemophagocytic lymphohistiocytosis (HLH).[1] The incidence of MAS is unknown as there is a wide spectrum of clinical manifestations, and episodes may remain unrecognized.
In many cases a trigger is identified, often a viral infection, or a medication.[2] There is uncontrolled activation and proliferation of macrophages, and T lymphocytes, with a marked increase in circulating cytokines, such as IFN-gamma, and GM-CSF. The underlying causative event is unclear, and is the subject of ongoing research. In many cases of MAS, a decreased natural killer cell (NK-cell) function is found.
In addition, other specific markers of macrophage activation (e.g. soluble CD163), and lymphocyte activation (e.g. soluble IL-2 receptor) can be helpful. NK cell function analysis may show depressed NK function, or, flow cytometry may show a depressed NK cell population.
[4]
The best treatment for MAS has not been firmly established. Most commonly used treatments include high-dose glucocorticoids, and cyclosporine. In refractory cases treatment regimens are used similar to that in HLH.
