Adult-onset Still’s disease presenting with atypical Kikuchi-Fujimoto disease-like histiocytic necrotizing lymphadenitis: a diagnostic pitfall

Adult-onset Still's disease (AOSD) may, in rare cases, present with the histopathological features of Kikuchi-Fujimoto disease, posing a significant diagnostic challenge and potentially leading to error.The persistence of systemic symptoms (spiking fever, severe polyarthralgia) and most critically, extreme hyperferritinaemia (often >5,000 μg/l) necessitate the immediate calculation of the H-score. A low H-score and the presence of neutrophilic leucocytosis are key factors in differentiating AOSD from macrophage activation syndrome (MAS) and hemophagocytic lymphohistiocytosis.This case highlights the necessity of rapid initiation of targeted immunosuppressive therapy (e.g., IL-1 inhibitors) to treat the underlying AOSD and prevent complications like MAS.