The differential diagnosis between rheumatic diseases and infectious conditions is a great challenge in clinical practice. Adult-onset Still's disease (AOSD) is a rare systemic inflammatory syndrome that shares several clinical and laboratory variables with sepsis. Interleukin (IL)-18 is overexpressed in AOSD, suggesting a possible role as a disease biomarker. The aim of our study was to detect IL-18 serum levels in a cohort of patients with AOSD and sepsis and to address its possible role as a biomarker for differential diagnosis.
A group of unselected patients with AOSD diagnosed according to the Yamaguchi criteria and consecutive patients with sepsis diagnosed according to the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference criteria were enrolled. The clinical and laboratory data were collected. In the AOSD group, disease activity was assessed by Pouchot's and Rau's criteria. IL-18 serum levels were detected by ELISA.
Thirty-nine patients with AOSD and 18 patients with sepsis were enrolled. Two out of 18 patients with sepsis (11.1%) also fulfilled the Yamaguchi criteria. A significant difference was found in IL-18 serum levels between patients with active and inactive disease (p < 0.001), and it positively correlated with disease activity (p = 0.0003), ferritin serum level (p = 0.016), and erythrocyte sedimentation rate (p = 0.041). IL-18 was significantly increased in patients with AOSD when compared with sepsis (p = 0.014). For a cutoff of 148.9 pg/ml, this test had a specificity of 78.3% and a sensitivity of 88.6%.
We have demonstrated that IL-18 can be a biomarker for differential diagnosis between AOSD and sepsis.