Adult-onset Still's disease in an 83-year-old patient with positive antinuclear antibodies: a case report.

Adult-onset Still's disease (AOSD) is a rare, systemic autoinflammatory disorder predominantly affecting young adults. It is characterized by polyarthritis, systemic inflammation with high spiking fevers, a transient salmon-pink rash, hepatosplenomegaly, and elevated ferritin levels. Its clinical presentation is highly heterogeneous and lacks specificity, and there are currently no unified diagnostic criteria. Differential diagnosis requires the exclusion of infections, malignancies, other rheumatic diseases, and adverse drug reactions. We report the case of a woman in her 80s in whom the diagnosis of adult-onset Still's disease was delayed owing to her advanced age, atypical rash, and positive antinuclear antibody status, despite significantly elevated serum ferritin levels. This case highlights that AOSD can affect older individuals, including those aged ≥ 80 years, and should be considered in the differential diagnosis of these patients when presenting with unexplained fever, especially if accompanied by rashes and hyperferritinemia. Moreover, a positive antinuclear antibody test does not rule out the diagnosis of AOSD. Timely and appropriate treatment can improve the prognosis of older patients with adult-onset Still's disease.