BACKGROUND: Adult-onset Still’s disease (AOSD) is a rare systemic inflammatory condition characterized by spiking fevers, evanescent rash, and arthritis, and it may be accompanied by pharyngalgia, lymph enlarged nodes, and splenomegaly. Viral infection is often thought to be a trigger, but the etiology and epidemiology are unknown or lacking. Adult-onset Still’s disease can present as self-limited, intermittent, or chronically, and can lead to severe complications. There is no specific clinical or laboratory test, and infection, malignancy, and other autoimmune diseases can mimic the clinical manifestation of AOSD, so the diagnosis is one of exclusion.
CASE REPORT: This case report describes a young female patient who presented with symptoms typical of Adult-onset Still’s disease, but was misdiagnosed as having a severe infection in the local clinical hospital at which she first sought care. We ruled out infection and other possible etiologies, and finally discussed her unusual clinical course and performed a full medical workup, which met the Yamaguchi Criteria. We made the final diagnosis of AOSD, and after treatment with nonsteroidal anti-inflammatory drugs, corticosteroids, and anti-rheumatic drugs, the patient experienced clinical and laboratory-verified remission.
CONCLUSIONS: Diagnosing AOSD is challenging due to the lack of typical pathognomonic symptoms and specific tests. This case illustrates the importance of considering autoimmune conditions when faced with a patient presenting with persistent fever of unknown origin.

Keywords: Arthritis, Exanthema, Rheumatic Fever, Still's Disease, Adult-Onset