Adult-onset still’s disease as a cause of pyrexia of unknown origin - A diagnostic dilemma

Pyrexia of unknown origin (PUO) continues to pose diagnostic challenges despite advancements in medical technology. Adult-onset Still’s Disease (AOSD), a rare systemic inflammatory disorder, remains an important but often overlooked cause. We report the case of a 42-year-old woman presenting with prolonged fever, inflammatory arthritis, and rash. Extensive evaluation excluded infectious, malignant, and common autoimmune causes. Marked hyperferritinemia and fulfillment of the Yamaguchi criteria led to a diagnosis of AOSD. The patient responded well to immunosuppressive therapy. AOSD should be considered in patients with PUO after the exclusion of common causes. Elevated serum ferritin and the Yamaguchi criteria are the key diagnostic tools.