Cholangioscopy-guided diagnosis and management of biliary cast syndrome in a nontransplant patient.

Background and Aims: Biliary cast syndrome (BCS) in nontransplant patients is rare and diagnostically challenging. We demonstrate the role of single-operator cholangioscopy (SOC) in managing BCS in a patient with rheumatoid arthritis (RA) and identifying an occult, high-risk molecular marker. Methods: A 54-year-old woman with RA presented with cholestatic liver dysfunction. After inconclusive imaging in a nondilated common bile duct, she underwent ERCP with SOC for diagnosis, multimodal cast removal, and targeted biopsy of the underlying mucosa. Results: SOC directly visualized a branching biliary cast in a nondilated duct, leading to a definitive diagnosis. The cast was completely extracted using multimodal techniques. Biopsies of the inflamed mucosa revealed reactive atypical hyperplasia with loss of Conclusions: SOC is indispensable for diagnosing and managing BCS when imaging is inconclusive. This case links systemic inflammation to BCS and highlights the importance of SOC-guided biopsy to detect high-risk molecular changes, such as