Unexpected diagnosis: IgG4-related sclerosing cholangitis with normal serum IgG4 levels - Unraveling diagnostic and therapeutic challenges.

Diagnosing IgG4-related sclerosing cholangitis (IgG4-SC) presents significant challenges, especially when serum IgG4 levels are normal and other organs are not involved. We report a case of a 51-year-old patient with typical symptoms of biliary obstruction, including jaundice and abdominal pain. Despite normal serum IgG4 levels, imaging suggested cholangiocarcinoma, leading to extensive surgical intervention. Histological analysis of the surgical specimen revealed extensive lymphoplasmacytic infiltration and numerous IgG4-positive plasma cells, confirming IgG4-SC. This case underscores the difficulty in differentiating IgG4-SC from other biliary diseases such as primary sclerosing cholangitis and cholangiocarcinoma, highlighting the need for thorough histological examination in atypical presentations.