The Deadly Masquerade: Unveiling the Fatal Facade of the Great Imitator.

Sclerosing cholangitis (SC) is a fibroinflammatory condition that results in the progressive narrowing and destruction of bile ducts. It is generally classified into three distinct types: primary sclerosing cholangitis (PSC), secondary cholangitis, and immunoglobulin G4 (IgG4)-related cholangitis (IRC). IgG4-sclerosing cholangitis (IgG4-SC) is a rare entity characterized by inflammation and strictures within the biliary tree, arising from host-mediated immune responses. This condition represents the biliary manifestation of IgG4-related disease and may mimic other forms of sclerosing cholangiopathy, as well as cholangiocarcinoma. The clinical presentations of these diseases exhibit significant overlap, and diagnosis can be challenging. This case report discusses a 67-year-old male patient diagnosed with isolated IgG4-SC, who was initially suspected of having either cholangiocarcinoma or PSC.