Derivation and validation of adult Still Activity Score (SAS)

Background/Aim: Adult-onset Still’s disease (AOSD) is a multi-systemic, autoinflammatory disorder. Several activity scores have been proposed but none of them have been adopted universally. Our aim was to create a clinician-friendly activity scoring system by using simple clinical and laboratory parameters. Methods: AODS patients according to Yamaguchi criteria were included in this cross-sectional, multi-center study. Derivation and validation cohorts were constituted. Demographic, clinical and laboratory evaluation at study visit; patients’, and physicians’ global assessments of disease activity (both VAS/ Likert scale) were recorded. To develop the score; ordinal logistic regression model was used to determine independent predictors of patient’ global assessments of disease activity. Clinically and statistically significant variables were weighted according to regression coefficients. Then, performance of the score was tested on the validation cohort. Results: Total of 197 consecutive AOSD patient (125 in derivation, 72 in validation cohorts) were included. Final Still Activity Score was fever (2 points), arthralgia (2 points, plus 1 point if arthritis was present in ≥2 joints), neutrophilia≥65% (1 point) and ferritin≥350 ng/mL (1 point) (maximum of 7 points). The SAS yielded an AUC value of 0.98(0.96-1.00) in the derivation cohort and 0.91(95%CI:0.85-0.98) in the validation cohort to discriminate high AOSD activity from moderate-inactive AOSD. Correlation of SAS with PtGA was 83% for the derivation cohort and 76% for the validation cohort. Conclusions: SAS has shown a good test performance to distinguish active AOSD patients from the others. SAS may be a useful method for evaluating disease activity of AOSD patients in daily practice. Funding: None to declare. Declaration of Interest: None to declare. Ethical Approval: The present study was conducted in compliance with the Helsinki Declaration and was approved by the Local Ethics Committee of Hacettepe University (GO- 20/824). A written informed consent form was completed by all participants.