Systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still’s disease (AOSD) are considered the same disease, but a common approach for diagnosis and management is still missing. Methods In May 2022, EULAR and PReS endorsed a proposal for a joint task force (TF) to develop recommendations for the diagnosis and management of sJIA and AOSD. The TF agreed during a first meeting to address four topics: similarity between sJIA and AOSD, diagnostic biomarkers, therapeutic targets and strategies and complications including macrophage activation syndrome (MAS). Systematic literature reviews were conducted accordingly. Results The TF based their recommendations on four overarching principles, highlighting notably that sJIA and AOSD are one disease, to be designated by one name, Still’s disease. Fourteen specific recommendations were issued. Two therapeutic targets were defined: clinically inactive disease (CID) and remission, that is, CID maintained for at least 6 months. The optimal therapeutic strategy relies on early use of interleukin (IL-1 or IL-6 inhibitors associated to short duration glucocorticoid (GC). MAS treatment should rely on high-dose GCs, IL-1 inhibitors, ciclosporin and interferon-γ inhibitors. A specific concern rose recently with cases of severe lung disease in children with Still’s disease, for which T cell directed immunosuppressant are suggested. The recommendations emphasised the key role of expert centres for difficult-to-treat patients. All overarching principles and recommendations were agreed by over 80% of the TF experts with a high level of agreement. Conclusion These recommendations are the first consensus for the diagnosis and management of children and adults with Still’s disease.

Objectives To analyse the similarity in clinical manifestations and laboratory findings between systemic juvenile idiopathic arthritis (sJIA) and adult-onset Still’s disease (AOSD). Methods Three systematic reviews (SR) were performed. One included cohort studies comparing sJIA versus AOSD that described clinical and biological manifestations with at least 20 patients in each group (SR1). The second identified studies of biomarkers in both diseases and their diagnostic performance (SR2). The last focused on diagnostic biomarkers for macrophage activation syndrome (MAS, SR3). Medline (PubMed), Embase and Cochrane Library were systematically searched. The risk of bias was assessed with an adapted form of the Hoy scale for prevalence studies in SR1 and the Quality Assessment of Diagnostic Accuracy Studies-2 in SR2 and SR3. We performed meta-analyses of proportions for the qualitative descriptors. Results Eight studies were included in SR1 (n=1010 participants), 33 in SR2 and 10 in SR3. The pooled prevalence of clinical manifestations did not differ between sJIA and AOSD, except for myalgia, sore throat and weight loss, which were more frequent in AOSD than sJIA because they are likely ascertained incompletely in sJIA, especially in young children. Except for AA amyloidosis, more frequent in sJIA than AOSD, the prevalence of complications did not differ, nor did the prevalence of biological findings. Ferritin, S100 proteins and interleukin-18 (IL-18) were the most frequently used diagnostic biomarkers, with similar diagnostic performance. For MAS diagnosis, novel biomarkers such as IL-18, C-X-C motif ligand 9, adenosine deaminase 2 activity and activated T cells seemed promising. Conclusion Our results argue for a continuum between sJIA and AOSD. PROSPERO registration number CRD42022374240 and CRD42024534021.

Adult-onset Still's disease (AOSD) is a rare systemic auto-inflammatory disorder in which management and treatment have considerably progressed over the past decade. Despite wide use of interleukin (IL)-1 or IL-6 inhibitors, serious complications remain possible. Areas covered: A comprehensive literature search in MEDLINE via Pubmed was performed to review AOSD's severe and sometimes life-threatening complications: reactive hemophagocytic lymphohystiocytosis, coagulation disorders, fulminant hepatitis, cardiac or pulmonary complications and amyloid A amyloidosis. Expert commentary: Early recognition and prompt management is essential to significantly decrease morbi-mortality. The key question is to determine whether the complication is related to the disease itself or related to or favored by (e.g. infection) the ongoing treatment. For all severe AOSD-related complications, high-dose corticosteroids and supportive measures remain the first-line treatment. In case of inadequate response, combination with IL-1 or IL-6 blockers is justified. Cyclosporine A and etoposide remain of interest, especially in case of reactive hemophagocytic lymphohysitocytosis. Plasma exchange may be useful in case of thrombotic microangiopathy. In the near future, new biologic or non-biologic drugs targeting IL-18 or other cytokines or kinases could be of help.