Diagnostic pitfalls in IgG4-related sclerosing cholangitis presenting as perihilar cholangiocarcinoma: case report with literature review.

Background: IgG4-related sclerosing cholangitis (IgG4-SC) is an uncommon autoimmune biliary disorder that often closely mimics malignant perihilar cholangiocarcinoma, posing significant diagnostic challenges. This case is notable for initially normal preoperative IgG4 levels, followed by profound postoperative elevation, with final confirmation through histopathology. It highlights the need for heightened clinical vigilance and multidisciplinary evaluation in patients with atypical biliary strictures. This report expands awareness of the variable presentations of IgG4-SC and offers practical insights for its differential diagnosis and management. Case summary: A 72-year-old Chinese man presented with persistent right upper abdominal pain and acute-onset jaundice. Initial imaging and laboratory findings indicated severe cholestasis and suggested perihilar cholangiocarcinoma. Extensive preoperative imaging, percutaneous drainage, and surgical exploration were performed. Postoperative pathology revealed marked plasma cell infiltration and storiform fibrosis in the bile duct wall, with immunohistochemistry confirming abundant IgG4-positive plasma cells and a marked postoperative serum IgG4 increase (>1,600 mg/dL). The final diagnosis was IgG4-SC. Initiation of corticosteroid therapy led to rapid clinical, biochemical, and radiological improvement, with no adverse events and sustained remission at 9 months of follow-up. Conclusion: Definitive diagnosis of IgG4-SC requires integration of histopathology, not solely serological markers, to avoid misdiagnosis.