Incidental Diagnosis of Erdheim–Chester Disease in a 42‐Year‐Old Man With Persistent Elevated ESR and Peri‐Ocular Xanthomas: A Case Report

Erdheim–Chester disease (ECD) is a rare non‐Langerhans cell histiocytosis characterized by multisystem involvement and frequent diagnostic delay due to nonspecific clinical manifestations. We report a 42‐year‐old asymptomatic man with persistently elevated erythrocyte sedimentation rate (ESR) detected during routine laboratory evaluation. Physical examination revealed bilateral peri‐ocular xanthomas. Multimodal imaging demonstrated bilateral perirenal soft‐tissue infiltration with a characteristic “hairy kidney” appearance on computed tomography, symmetric skeletal involvement on bone scintigraphy, and metabolically active lesions on 18 F‐FDG PET/CT. Histopathological examination of a peri‐ocular xanthoma biopsy revealed CD68‐positive, CD1a‐negative foamy histiocytes, confirming the diagnosis of Erdheim–Chester disease. Given the patient's oligosymptomatic presentation and absence of critical organ involvement, a watch‐and‐wait strategy with close surveillance was adopted. This case highlights the diagnostic value of subtle clinical findings, such as isolated inflammatory marker elevation and peri‐ocular xanthomas, and emphasizes the importance of accessible tissue biopsy combined with characteristic imaging features for early diagnosis of ECD.