Steroid-Refractory Adult-Onset Still's Disease: A Case Report.

Adult-onset Still's disease (AOSD) is one of the systemic autoinflammatory disorders characterised by an evanescent salmon-pink rash, high spiking fevers, and inflammatory arthritis. AOSD is driven by dysregulated immune activation involving excess pro-inflammatory cytokines, specifically IL-1β and IL-18. Current consensus recognises AOSD and systemic juvenile idiopathic arthritis as a continuous disease spectrum. Because it lacks a definitive biomarker and mimics other severe conditions, AOSD remains a diagnosis of exclusion; early recognition is paramount to prevent complications including macrophage activation syndrome and haemophagocytic lymphohistiocytosis. We report the case of a 23-year-old man presenting with persistent pyrexia of unknown origin, an evanescent rash, inflammatory monoarthritis, marked neutrophilic leukocytosis, and profound hyperferritinaemia. Following an extensive multidisciplinary investigation to exclude connective tissue disease, malignancy, and infection, the patient successfully fulfilled the Yamaguchi classification criteria for AOSD. This case highlights the inherent diagnostic challenges associated with Still's disease. It demonstrates the critical importance of early multidisciplinary assessment and the timely escalation to targeted cytokine-directed therapies to achieve disease remission.