IgG4-related Sclerosing Cholangitis Masquerading as Cholangiocarcinoma: A Diagnostic Challenge.

BACKGROUND: IgG4-related sclerosing cholangitis (IgG4-SC) is a rare immune-mediated disorder affecting the biliary tree and leading to biliary strictures that may resemble cholangiocarcinoma (CCA). CASE PRESENTATION: An elderly man presented with a one-week history of jaundice, pale stool, and dark urine. This was associated with unintentional weight loss over the past year. Laboratory findings were notable for cholestasis and significantly elevated CA19-9. Imaging demonstrated multiple diffuse biliary strictures of malignant appearance. Cytology showed atypical glandular cells. The patient was misdiagnosed with CCA and was assessed for a possible surgical intervention or chemoradiotherapy. However, the patient was eventually diagnosed with IgG4-SC after a high serum IgG4 level and liver biopsy. The patient responded well to steroids. CONCLUSION: This case underscores the diagnostic dilemma posed by IgG4-SC, particularly in elderly patients with cholestatic jaundice and elevated CA 19-9, which can be misleading for malignancy.