RT Journal Article SR Electronic T1 Development and initial validation of the MS score for diagnosis of macrophage activation syndrome in systemic juvenile idiopathic arthritis JF Annals of the Rheumatic Diseases JO Ann Rheum Dis FD BMJ Publishing Group Ltd and European League Against Rheumatism SP 1357 OP 1362 DO 10.1136/annrheumdis-2019-215211 VO 78 IS 10 A1 Francesca Minoia A1 Francesca Bovis A1 Sergio Davì A1 AnnaCarin Horne A1 Michel Fischbach A1 Michael Frosch A1 Adam Huber A1 Marija Jelusic A1 Sujata Sawhney A1 Deborah K McCurdy A1 Clóvis A Silva A1 Donato Rigante A1 Erbil Unsal A1 Nicolino Ruperto A1 Alberto Martini A1 Randy Q Cron A1 Angelo Ravelli A1 , YR 2019 UL http://ard.bmj.com/content/78/10/1357.abstract AB Objective To develop and validate a diagnostic score that aids in identifying macrophage activation syndrome (MAS) in patients with systemic juvenile idiopathic arthritis (sJIA).Methods The clinical and laboratory features of 362 patients with sJIA-associated MAS and 404 patients with active sJIA without evidence of MAS were collected in a multinational collaborative project. Eighty percent of the study population was used to develop the score and the remaining 20% constituted the validation sample. A Bayesian Model Averaging approach was used to assess the role of each clinical and laboratory variables in the diagnosis of MAS and to obtain the coefficients of selected variables. The final score, named MAS/sJIA (MS) score, resulted from the linear combination of these coefficients multiplied by the values of each variable. The cut-off that best discriminated MAS from active sJIA was calculated by means of receiver operating characteristic (ROC) curve analysis. Score performance was evaluated in both developmental and validation samples.Results The MS score ranges from −8.4 to 41.8 and comprises seven variables: central nervous system dysfunction, haemorrhagic manifestations, active arthritis, platelet count, fibrinogen, lactate dehydrogenase and ferritin. A cut-off value ≥−2.1 revealed the best performance in discriminating MAS from active sJIA, with a sensitivity of 0.85, a specificity of 0.95 and a kappa value of 0.80. The good performance of the MS score was confirmed in the validation sample.Conclusion The MS score is a powerful and feasible tool that may assist practitioners in making a timely diagnosis of MAS in patients with sJIA.