Hilar cholangiocarcinoma associated with immunoglobulin G4-positive plasma cells and elevated serum immunoglobulin G4 levels.

Immunoglobulin G4 (IgG4)-related disease is a fibroinflammatory systemic disorder with multiorgan involvement. Proximal bile duct involvement results in IgG4-related sclerosing cholangitis, which is characterized by a lymphoplasmacytic infiltrate with abundant IgG4-positive plasma cells and fibrosis. Differentiating between cholangiocarcinoma and IgG4-sclerosing cholangitis can present a diagnostic dilemma. We describe an unusual presentation of a hepatic mass meeting multiple criteria for IgG4-sclerosing cholangitis but was ultimately found to be cholangiocarcinoma. Several published case reports describe patients with suspected cholangiocarcinoma who are later found to have IgG4-sclerosing cholangitis, but few reports have demonstrated the reverse. Distinguishing between cholangiocarcinoma and IgG4-sclerosing cholangitis is challenging, and a high clinical suspicion for cholangiocarcinoma must always be maintained. (Hepatology Communications 2018;2:349-353).