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IgG4-related disease (IgG4-RD) is a recently recognized fibroinflammatory condition characterized by tumefactive lesions with dense lymphoplasmacytic infiltrate rich in IgG4-positive plasma cells and often elevated serum IgG4 concentrations. Autoimmune pancreatitis (type 1) and IgG4-related sclerosing cholangitis are the pancreatobiliary manifestations of IgG4-RD. Patients with IgG4-RD often present with obstructive jaundice, weight loss, and abdominal pain. Due to its tumefactive nature and clinical presentations, IgG4-RD of the pancreatobiliary system is often disguised as pancreatobiliary malignancies. Endoscopic evaluations are important for the diagnosis of IgG4-RD of the pancreatobiliary system and for the differentiation of IgG4-RD from malignancies. Available endoscopic tools include endoscopic ultrasonography (EUS), EUS elastography, contrast-enhanced EUS, intraductal ultrasonography (IDUS) of the bile duct wall, and endoscopic retrograde cholangiopancreatography (ERCP). Characteristic endoscopic retrograde pancreatography features of IgG4-RD of the pancreatobiliary system that are useful in the differentiation from pancreatic cancer are a long stricture of the main pancreatic duct, lack of upstream dilatation from the stricture, and multifocal strictures with intervening normal-looking duct. EUS findings of diffuse hypoechoic area, diffuse enlargement, peripancreatic hypoechoic margin and bile duct wall thickening are more frequently found in IgG4-RD than in pancreatic cancer. However, the EUS morphologic spectrum is diverse in IgG4-RD. New imaging techniques such as EUS-elastography and contrast-enhanced EUS may have the potential to allow more reliable distinction between IgG4-RD and pancreatic malignancies. The specific IDUS findings for differentiating IgG4-RD from cholangiocarcinoma is thickening of the bile duct wall (exceeding 1mm) in a bile duct that is dilated and/or nonstenotic on endoscopic retrograde cholangiography. Endoscopic diagnostic sample acquisition at EUS/ERCP may give a confirmative diagnosis of pancreatobiliary malignancy or suggest a diagnosis of IgG4-RD. The recommended first-line procedure to exclude malignancy is EUS-guided fine needle aspiration in cases where sampling of a suspected pancreatic cancer is indicated, while ERCP-guided sampling is recommended in cases where sampling of a suspected bile duct cancer is indicated, particularly when ERCP is needed to relieve obstructive jaundice. IgG4 immunostaining of the biopsy sample is often used to support the diagnosis of IgG4-RD. However, the result of positive IgG4 immunostaining in isolation does not necessarily qualify for the diagnosis of IgG4-RD. The diagnosis of IgG4-RD requires cautious correlation with the histopathological features in the sample, as well as with other cardinal features of IgG4-RD. |
