Development of new classification criteria for macrophage activation syndrome complicating systemic juvenile idiopathic arthritis

Abstract

Introduction: Macrophage activation syndrome (MAS) is a potentially fatal complication of systemic juvenile idiopathic arthritis (sJIA), whose prompt recognition and treatment are critical. However, early diagnosis of MAS is often challenging and none of the current diagnostic criteria is satisfactory. An international project aimed to develop a new set of classification criteria for MAS was recently started. Objective(s): To present the results of the consensus conference that led to the development of the new classification criteria for MAS complicating sJIA. Method(s): 28 pediatric specialists (20 rheumatologists and 8 hematooncologists) with expertise in MAS reviewed 428 profiles of patients with sJIA-associated MAS or with a confusable condition (active sJIA or systemic infection). The expert panel classified each patient as having or not having MAS based on clinical and laboratory features at disease onset. Using the experts' consensus as "gold standard", a statistician tested 982 candidate definitions, derived from both literature and statistical analyses. Definitions with a kappa level of agreement >= 0.85 were included in the expert voting process during the consensus conference. In a secondary analysis, experts were asked to declare whether the change in laboratory parameters over time was consistent or not with MAS and to rank laboratory tests in order of the importance of their change in the diagnosis of MAS. Result(s): After 5 rounds, experts achieved consensus on approximately 90% (391/428) of the profiles submitted. Statistical analyses led to select 45 definitions with kappa >= 0.85. During the consensus conference, 7 voting sessions were made. Finally consensus (82%) was reached on the following definition: "A febrile patient with known or suspected sJIA is classified as having MAS if the patient has: ferritin >684 ng/mL and at least 2 of the following 4 laboratory abnormalities: platelets 48 U/L, triglycerides >156 mg/dL, and fibrinogen