The macrophage activation syndrome: a new entity, a potentially fatal complication of rheumatic disorders.

To review the precipitating events, clinical feature, treatment and outcome of macrophage activation syndrome (MAS). Activation of macrophages resulting from the secondary hemophagocytic syndrome is a rarely reported complication. It was first described in rheumatic diseases in children. The available reliable information on this rare, poorly understood and potentially fatal entity shows MAS to be a complication of the systemic onset juvenile idiopathic arthritis, of systemic lupus erythematosus (SLE) and some other rheumatic diseases. The disruption of the macrophage-lymphocyte interactions leads to uncontrolled proliferation of highly activated macrophages. This secondary reactive hemophagocytic syndrome, referred to as MAS in the current medical terminology, can be a complication either of the rheumatic disease associated syndrome (RAHS), or of the infection associated form (IAHS) and malignancy associated form (MAHS). These three forms are clinically almost identical. High grade fever, hepatosplenomegaly, lymphadenopathy, rash due to refractory thrombocytopenia, mild disseminated intravascular coagulation are the common clinical features in this disorder. Bone marrow studies shows high percentage of non-malignant mature histiocytes which have phagocytized erythrocytes, as well as leukocytes and thrombocytes. Mortality rate of MAS is very high. Early treatment with glucocorticoids, cyclosporin, anti-TNF agents, ATG may induce a prolonged remission. Allogenic bone marrow transplantation leads to a definitive cure.