RT Journal Article SR Electronic T1 AB0286 14 cases study of macrophage activation syndrome (MAS) in systemic onset juvenile idiopathic arthritis JF Annals of the Rheumatic Diseases JO Ann Rheum Dis FD BMJ Publishing Group Ltd and European League Against Rheumatism SP 1148 OP 1149 DO 10.1136/annrheumdis-2017-eular.1791 VO 76 IS Suppl 2 A1 X Chen A1 H Zeng YR 2017 UL http://ard.bmj.com/content/76/Suppl_2/1148.3.abstract AB Background Macrophage activation syndrome (MAS) is a severe, potentially life-threatening syndrome.Objectives we aim to review the precipitating events,clinical features, treatment, and outcome of macrophage activation syndrome (MAS).Part patients were analysed the Polymorphisms of Perforin A91V (NCBI:SNP rs35947132) using special primers by polymerase chain reaction (PCR).Methods Retrospective review of cases of MAS from a prospectively collected database of children with autoimmune diseases from 2003 to 2008.Results Fourteen patients (nine boys) were considered to have evidence of MAS.The primary diagnosis was systemic onset juvenile idiopathic arthristis, with age ranged from 5 months to 12 years. No medication was identified as trigger. Eleven had infections prior to MAS,specific infectious agents were identified in four. High grade fever, new onset hepatosplenomegaly, lymphadenopathy, dysfunction of liver,abnormal fat metabolism and hemophagocytosis were common clinical features.Two cases were with ARDS and MOF in three and three died. The perforin A91V (NCBI:SNP rs35947132) gene was detected in seven systemic onset juvenile idiopathic arthritis compolicated with MAS cases, but no mutation were found. Glucocorticoid, intravenous immunoglobulin, immunoimpressive therapy were effective and HP (Plasmapheresis) used in one serious case was also effective.Conclusions MAS is a rare and potentially fatal complication of childhood rheumatoid diseases,especially systemic onset juvenile idiopathic arthritis. Most of our patients were male, and most cases were preceded by infection. Bone marrow studies support the diagnosis. MOF may be a poor prognostic sign.Aggressive early therapy is essential.Disclosure of Interest None declared