JAK inhibitors in difficult-to-treat adult-onset Still’s disease and systemic-onset juvenile idiopathic arthritis

Abstract Objectives Excessive and inappropriate production of pro-inflammatory cytokines plays a key role in Still’s disease. JAK inhibitor (JAKi) agents mainly block pro-inflammatory cytokine pathways, notably IL-6 and IFN. The objective was to assess the efficacy and safety of JAKi agents in difficult-to-treat systemic juvenile idiopathic arthritis (SJIA) or adult-onset Still's disease (AOSD). Methods This retrospective study was based on a national survey conducted in the departments of rheumatology, paediatric rheumatology and internal medicine of French hospitals regarding SJIA and AOSD patients who received JAKi agents. The data were collected with a standardised questionnaire and analysed at different times (treatment initiation, months 1, 3, and 6 and the end of follow-up). Results Nine patients (7 adults) were included. All patients showed inadequate response to corticosteroids or conventional synthetic or biologic disease-modifying anti-rheumatic drugs. Baricitinib was used in 5 patients, ruxolitinib in 2, tofacitinib in 2, and upadacitinib in 1. A JAKi was used combined with corticosteroids in all but 2 patients. A JAKi was associated with anakinra and corticosteroids in one patient, and with methotrexate, anakinra and corticosteroids in another. The median follow-up was 16 [1–33] months. Two cases out 9 showed complete remission, 3/9 partial response and 4/9 treatment failure. At the last visit, corticosteroids could be decreased but not stopped. Tolerance of the JAKi was acceptable (no severe adverse events). Conclusion JAKi agents may be a therapeutic option for some patients with difficult-to-treat Still’s disease, especially those with partial response to medium- or high-dose corticosteroids or biologics.