Abstract
Tocilizumab（TCZ）， a humanized anti-IL-6 receptor monoclonal antibody，is an effective cytokine
inhibitor fbr the treatment of juvenile idiopathic arthritis（JIA）． However， macrophage-activation syndrome
（MAS）has been observed as a complication in some cases of systemic-JIA during TCZ therapy In this report， we
described the clinical courses of 5 cases of MAS during TCZ therapy and demonstrated the need fbr monitoring
serum interleukin（IL）-18concentrations． Clinical symptoms of patients with s-JIA receiving TCZ were
apparently mild compared to those not receiving TCZ， Furthermore， serum CRP concentrations never increased
during TCZ therapy， even in MAS． Serum IL-18concentrations extremely elevated over 10,000 pg/mL in MAS．
Serum IL-18 concentrations increased persistently before the other measures of disease activity． The clinical
symptoms of MAS and s－JIA could be masked during TCZ therapy；hence， monitoring serum concentrations of
IL-18 is recommended for the evaluation of disease activity in s-JIA．
