Abstract
Immunoglobulin G4-related disease is a multisystem disorder with unique gastrointestinal tract manifestations, often simulating neoplasms and other inflammatory conditions. Appropriate clinical suspicion and application of internationally validated criteria can assist in making the proper diagnosis. This article describes two cases of patients presenting with biliary tract manifestations simulating lymphoproliferative disease and adenocarcinoma, respectively. Clinical, radiological, and histopathological findings ultimately led to the correct diagnosis, and revealed useful nuances for detection of future cases. Application of specific criteria, such as the classic Japan Biliary Association clinical diagnostic criteria published in 2012 and revised in 2020 as well as the 2019 American College of Rheumatology and European League Against Rheumatism (ACR/EULAR) classification criteria, has limitations but provides important warnings to be considered in the diagnostic journey of these challenging cases.