• Masaki Shimizu, Mao Mizuta, Nami Okamoto, Takahiro Yasumi, Naomi Iwata, Hiroaki Umebayashi, Yuka Okura, Noriko Kinjo, Tomohiro Kubota, Yasuo Nakagishi, Kenichi Nishimura, Mariko Mohri, Masato Yashiro, Junko Yasumura, Hiroyuki Wakiguchi, and Masaaki Mori.
• Department of Pediatrics, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takaramachi, Kanazawa, 920-8641, Japan. shimizum@staff.kanazawa-u.ac.jp.
• Pediatr Rheumatol. 2020 Jan 10; 18 (1): 2.

BackgroundThis study aimed to determine the influence of tocilizumab (TCZ) in modifying the clinical and laboratory features of macrophage activation syndrome (MAS) complicating systemic juvenile idiopathic arthritis (s-JIA). Furthermore, we assessed the performance of the 2016 MAS classification criteria for patients with s-JIA-associated MAS while treated with TCZ.MethodsA panel of 15 pediatric rheumatologists conducted a combination of expert consensus and analysis of real patient data. Clinical and laboratory features of s-JIA-associated MAS in 12 TCZ-treated patients and 18 untreated patients were evaluated. Possible MAS was defined as having characteristic laboratory features but lack of clinical features of MAS, or atypical MAS, or early treatment that prevented full-blown MAS.ResultsClinically, the TCZ-treated patients with s-JIA-associated MAS were less likely febrile and had significantly lower ferritin, triglyceride, and CRP levels than the untreated patients with s-JIA-associated MAS. Other laboratory features of MAS including lower platelet counts and lower fibrinogen were more pronounced in TCZ-treated patients. The TCZ-treated patients with s-JIA-associated MAS were less likely to be classified as MAS based on the MAS classification criteria (25% vs 83.3%, p < 0.01). This is ascribed to the absence of fever or insufficient ferritin elevation, compared with the untreated patients.ConclusionTCZ could modify the clinical and laboratory features of s-JIA-associated MAS. When evaluating the s-JIA patients while treated with TCZ, it is not applicable to use MAS classification criteria. Care must be taken to not underdiagnose MAS based on the MAS classification criteria.

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