Endoscopic diagnosis of immunoglobulin G4-related sclerosing cholangitis.

Immunoglobulin G4 (IgG4)-related sclerosing cholangitis (IgG4-SC) is a distinct form of sclerosing cholangitis frequently associated with autoimmune pancreatitis and is recognized as a biliary manifestation of IgG4-related disease. Endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasonography (EUS) are key diagnostic modalities for IgG4-SC. Cholangiocarcinoma and primary sclerosing cholangitis (PSC) are significant mimickers of IgG4-SC. ERCP is employed to evaluate narrowing of the bile duct, with cholangiograms of IgG4-SC classified into four types. This cholangiographic classification is crucial for differential diagnosis. Characteristic cholangiographic findings of IgG4-SC include diffuse or segmental strictures of the intrahepatic or extrahepatic bile ducts and intrahepatic strictures associated with autoimmune pancreatitis. ERCP is particularly useful for differentiating IgG4-SC from PSC because their cholangiographic features differ. EUS and intraductal ultrasonography (IDUS) are used to assess thickening of the bile duct wall. Characteristic IDUS findings in IgG4-SC include circular and symmetrical wall thickening, smooth outer and inner margins, and homogeneous internal echoes at stricture sites. Additionally, bile duct wall thickening at nonstricture sites is a typical IDUS feature of IgG4-SC. Bile duct biopsy is used to evaluate pathological findings, although its diagnostic yield for IgG4-SC is limited; its primary role is to exclude malignant biliary strictures. Duodenal papilla biopsy serves as a supplementary diagnostic tool for IgG4-SC. EUS and tissue acquisition also aid in diagnosing autoimmune pancreatitis as part of other organ involvement. Thus, endoscopic techniques play critical roles in the diagnosis of IgG4-SC.