Objectives: Adult-onset Still's disease (AOSD) phenotype appears to be dichotomized in systemic or chronic articular forms. As biologicals and particularly interleukin (IL)-1 and IL-6 blockers play a more and more prominent role in the treatment, their place requires clarification. This study aimed to identify factors predictive of treatment response to anakinra or tocilizumab and investigate whether the choice of biotherapy and delays in the initiation of biotherapy influenced the likelihood of steroid discontinuation. Methods: A multicenter exploratory retrospective study included all patients diagnosed with AOSD and receiving biological treatments in three regional hospitals until 2018. Clinical and biological characteristics at diagnosis and treatment-related data were collected. The nonparametric Mann-Whitney test was used to perform univariate analysis for quantitative variables, and Fisher's exact test was used for qualitative variables. Results: Twenty-seven patients were included. All but one patient achieved remission with either anakinra or tocilizumab. Treatment responses depended on disease phenotype: the presence of arthritis and a chronic articular phenotype were associated with a substantial response to tocilizumab with p = 0.0009 (OR 36 [2.6-1703]) and p = 0. 017 (OR 10 [1.22-92.6]), respectively, whereas the systemic form and the absence of arthritis were associated with a substantial response to anakinra with p = 0.0009 (OR 36 [2.6-1703]) and p = 0.017 (OR 10 [1.22-92.6]), respectively. Tocilizumab increased the likelihood of corticosteroid withdrawal (p = 0.029) regardless of delays in initiation or when it was initiated relative to other treatment in the overall therapeutic strategy. Conclusion: This study highlights the therapeutic implications of the phenotypic dichotomy of AOSD and should help us better codify AOSD treatment.

Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.