Diagnosis of adult-onset Still's disease (AOSD) is difficult because of a lack of pathognomonic findings and markers. The aim of this study was to investigate the efficacy of interleukin (IL)-18 and free IL-18 in the diagnosis and follow-up of patients with AOSD.
Levels of inflammatory cytokines, IL-18, IL-18 binding protein (IL-18BP), and free IL-18 were compared in 80 AOSD patients and 90 controls. The AOSD patients were divided into active and inactive groups according to disease activity, and the inactive patients were subdivided into a remission subgroup and a low disease activity subgroup. We compared erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), ferritin, IL-18, and free IL-18 as disease activity markers in the AOSD patients. Serial serum levels of activity markers were measured in 52 of the 80 AOSD patients at 3- to 6-month intervals.
There were significantly higher levels of IL-18 and free IL-18 in the AOSD patients than in the controls. IL-18 and free IL-18 were significantly higher in the active group than the inactive group (p < 0.001 for all). Unlike other activity markers, IL-18 and free IL-18 levels in the low disease activity subgroup were significantly higher than those in the remission subgroup within the inactive group (p = 0.004 and 0.005, respectively). During serial follow-up, ferritin and IL-18 showed a significant decrease in the responder and remission subgroup.
IL-18 might be an efficient marker for diagnosis and follow-up of AOSD and might also be a useful predictor of remission, especially in clinically inactive patients.