Adult-Onset Still's Disease: A Diagnostic Odyssey and Therapeutic Triumph.

Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder defined by quotidian fevers, arthralgia, and marked hyperferritinemia, often mimicking infectious, autoimmune, or malignant conditions. We present a diagnostically challenging and clinically instructive case involving a 34-year-old man with persistent fevers, systemic inflammation, and hepatic dysfunction. Despite extensive investigation, infectious and autoimmune etiologies were excluded. The diagnostic breakthrough emerged upon identification of profound hyperferritinemia (6,900 ng/mL), prompting the diagnostic consideration of AOSD. Initiation of corticosteroid therapy led to rapid symptom resolution and biochemical normalization. This case underscores the vital role of pattern recognition, diagnostic exclusion, and timely immunosuppression in AOSD. We emphasize the importance of early ferritin assessment and highlight regional diagnostic biases, particularly among darker-skinned individuals, in whom rash may be absent or underrecognized.