Case Report: Breaking the diagnostic dilemma of “lymphoma-like” presentation: a case of adult-onset Still's disease characterized by generalized lymphadenopathy and extremely elevated ferritin

Adult-onset Still's disease (AOSD) is a rare autoinflammatory condition whose symptoms often overlap with other diseases, particularly lymphoma. The article describes a case of a 53-year-old Chinese female patient presenting with fever, transient rash, generalized lymphadenopathy, and splenomegaly. PET/CT imaging showed increased metabolic activity in lymph nodes, spleen, and bone marrow, with extremely elevated ferritin levels of 15,485 ng/mL, raising suspicion for lymphoma. However, lymph node biopsy excluded the presence of lymphoma. Based on typical clinical presentation and laboratory findings, the patient was diagnosed with AOSD according to Yamaguchi classification criteria. Glucocorticoid therapy rapidly normalized temperature, the rash disappeared, lymph nodes decreased in size, and ferritin and inflammatory markers significantly decreased. The case demonstrates the importance of lymph node biopsy in AOSD with lymphoma-like imaging features and the critical role of ferritin as a biomarker.