Validation of Classification Criteria of Macrophage Activation Syndrome in Japanese Patients With Systemic Juvenile Idiopathic Arthritis.

Objective To validate whether the 2016 ACR/EULAR classification criteria of macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (s-JIA) is practical in the real world. Methods A combination of expert consensus and analysis of real patient data was conducted by a panel of 15 paediatric rheumatologists. Sixty five profiles comprised 18 patients with s-JIA–associated MAS and 47 patients with active s-JIA without evidence of MAS. From these profiles, 10 patient data points for full-blown MAS, 11 patient data points for MAS onset and 47 patient data points for acute s-JIA without MAS were evaluated. Results Evaluation of the classification criteria to discriminate full-blown MAS from acute s-JIA without MAS showed a sensitivity of 1.000 and specificity of 1.000 at the time of full-blown MAS. Sensitivity was 0.636 and specificity 1.000 at the time of MAS onset. The number of measurement items that fulfilled the criteria increased in full-blown MAS compared to that at MAS onset. At MAS onset, the positive rates of patients who met the criteria for platelet counts and triglycerides were low, whereas those for aspartate aminotransferase was relatively high. At full-blown MAS, the number of patients who met the criteria for each measurement item increased. Conclusion The classification criteria for MAS complicating s-JIA had a very high diagnostic performance. However, the diagnostic sensitivity for MAS onset was relatively low. For the early diagnosis of MAS in s-JIA, the dynamics of laboratory values during the course of MAS should be further investigated. This article is protected by copyright. All rights reserved.