Adult-onset Still’s disease remains a diagnostic challenge: a case report

Adult-onset Still’s disease is a diagnostic challenge. A 22-year-old female of Kenyan ethnicity with a fever of unknown origin was diagnosed with adult-onset Still’s disease (AOSD) following an extensive evaluation for persistent high-grade fever and rash. Her clinical presentation included lymphadenopathy, elevated ferritin (> 6000 µg/L), white blood cell count (WBC) (20.6 k/cmm), CRP (122.3 mg/L), ALT (133 U/L), AST (154 U/L), and negative workup for infection, malignancy, or other autoimmune disorders, initially raising concern for hemophagocytic lymphohistiocytosis (HLH) or macrophage activation syndrome (MAS). She responded appropriately to steroids, but shortly after completing a steroid taper, she developed a recurrence of high-grade fever, rash, and inflammatory arthritis symptoms. With infectious and malignant causes excluded, this recurrence of symptoms prompted a diagnosis of adult-onset Still’s disease (AOSD), and the initiation of the IL-1 inhibitor. She ultimately required transition to an IL-6 inhibitor for disease control. This case highlights the diagnostic complexities of differentiating autoinflammatory syndromes like AOSD from other inflammatory and infectious conditions in a patient who presents with fever of unknown origin, as well as reviewing treatment options for complex AOSD.