A case of adult-onset Still's disease in a patient after a car accident.

Key Clinical Message: Adult-onset Still's disease is a rare inflammatory condition with diverse clinical features. Yamaguchi criteria aid diagnosis, and pleural effusion and elevated ferritin levels are important markers. Steroids are the first-line treatment. Abstract: Adult-onset Still's disease (AOSD) is a rare systemic inflammatory condition with an unknown etiology. It is characterized by, spiking fever, arthritis, evanescent rash, sore throat, serositis, hepatomegaly, splenomegaly, and lymphadenopathy. It is a diagnosis of exclusion and has infections, systemic autoimmune and inflammatory rheumatic diseases, malignancy, and adverse drug reactions as its differential diagnosis. Because of these characteristics, diagnosis is frequently delayed, posing a significant challenge for physicians. While several classification criteria can be used to diagnose Still's disease, they have limitations in terms of sensitivity and specificity. The Yamaguchi criteria are considered the most sensitive and commonly used, requiring the presence of at least five characteristics, with at least two being major diagnostic criteria. Steroid therapy is the first-line treatment for AOSD patients. In this case report, we present a 56-year-old female patient who developed pleurisy a few months after a car accident, subsequently diagnosed with adult-onset Still's disease.