IgG4-sclerosing cholangitis masquerading as cholangiocarcinoma: a case report of an unresolved preoperative diagnosis.

Background: Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated chronic fibroinflammatory condition that can affect multiple organ systems. IgG4-related sclerosing cholangitis (IgG4-SC) is its manifestation involving the biliary tract. Due to atypical clinical presentations in some cases and insufficient awareness among clinicians, IgG4-SC is frequently misdiagnosed as cholangiocarcinoma, and multiple instances of inappropriate treatment as a result have been documented. Case presentation: Here we report a case of IgG4-SC that presented diagnostic challenges preoperatively and was followed by rare pancytopenia after surgery. The patient was a 50-year-old man who sought medical attention due to elevated transaminases for eight months, without obvious clinical symptoms. Among serum tumor markers, the level of protein induced by vitamin K absence/antagonist-II (PIVKA-II) was elevated. Examinations including magnetic resonance cholangiopancreatography (MRCP), contrast-enhanced abdominal computed tomography (CT), and positron emission tomography-computed tomography (PET-CT) all suggested malignant stricture at the hepatic hilum. A needle biopsy indicated dysplastic changes but was inconclusive for cholangiocarcinoma. Although IgG4-SC was considered, multiple serum IgG4 measurements remained within the normal range. With an initial clinical diagnosis of cholangiocarcinoma, the patient underwent surgical resection. Intraoperative frozen section analysis indicated an inflammatory process. Postoperatively, the patient developed pancytopenia that responded poorly to conventional supportive treatment. The condition was ultimately diagnosed as IgG4-SC based on postoperative histopathology. Corticosteroid therapy led to the normalization of the patient's blood counts, transaminases, and bilirubin levels. Conclusion: IgG4-SC can present with a spectrum of atypical features, such as isolated biliary strictures, absence of characteristic symptoms, normal IgG4 levels, and imaging findings resembling cholangiocarcinoma. Therefore, in cases clinically suspicious for cholangiocarcinoma, differentiating IgG4-SC warrants serious consideration. Every effort should be made to complete preoperative biopsy and histopathological assessment. For cases where differentiation remains difficult despite comprehensive evaluation, surgical intervention with intraoperative frozen section biopsy is necessary to establish a definitive diagnosis and avoid delayed treatment. Furthermore, this case suggests that IgG4-SC may also involve the hematopoietic system, manifesting as pancytopenia, which can respond effectively to corticosteroid therapy.