Paraneoplastic Adult‐Onset Still's Disease Caused by Mediastinal Lymph Node Carcinoma of Unknown Primary Site, Most Likely Lung Adenocarcinoma

A 73-year-old man presented with fever, polyarthritis and erythema on his back (Figure 1A) and extremities (Figure 1B).Laboratory findings showed leukocytosis and elevated CRP (24 mg/dL), white blood cell (11 800/μL; neutrophil (88%)), GOT (78 U/L), GPT (89 U/L), LDH (382 U/L), ferritin (1023 ng/mL) and IL-6 (143 pg/mL).Autoantibodies were all negative.Contrast enhanced CT revealed swollen mediastinal lymph nodes and pericardial effusion.