Tocilizumab improved both clinical and laboratory manifestations except for interleukin-18 in a case of multiple drug-resistant adult-onset Still's disease.

A patient with adult-onset Still's disease (AOSD) resistant to multiple drugs was treated in our hospital. Even biologics that block tumor necrosis factor (TNF) were ineffective. However, this patient responded quite well to tocilizumab, an interleukin (IL)-6 receptor blocker, suggesting that it is among the promising candidate drugs for multiple-drug resistant AOSD. Although the serum levels of most inflammatory markers such as C-reactive protein (CRP) and ferritin were reduced promptly by tocilizumab, that of IL-18 remained high. Thus, IL-18 is considered to have a further upstream position than IL-6 or to be at the same level as IL-6 in the inflammatory cascade of AOSD. This finding casts light on the pathogenesis of AOSD, and drugs that target IL-18 may prove beneficial in the treatment of this inflammatory disease.