Autoimmune polyglandular syndrome type 3B: a key to diagnosing autoimmune gastritis and asymptomatic primary biliary cholangitis

Background: Autoimmune polyglandular syndrome type 3 (APS-3) encompasses autoimmune thyroid disease and other autoimmune disorders. APS-3 is further categorized into four subtypes, with APS-3B involving gastrointestinal autoimmune diseases. In this case, we diagnosed autoimmune gastritis, a condition challenging to identify based on endoscopic findings alone, and asymptomatic primary biliary cholangitis (PBC) through the recognition of APS-3B. Case report: An 84-year-old female patient presented with forgetfulness and a history of Hashimoto’s disease. Although endoscopy revealed pan-atrophic gastritis, autoimmune gastritis was suspected rather than Helicobacter pylori infection due to consideration of the APS-3 framework. Specific observations, including adherent mucus and remnants of oxyntic mucosa, guided tests for anti-endogenous antibodies, confirming autoimmune gastritis. Recognizing APS-3B prompted further evaluation for PBC, including measurement of anti-mitochondrial M2 antibody, which led to the diagnosis of asymptomatic PBC. Conclusion: Recognition of APS-3 offers a valuable framework for the differential diagnosis of autoimmune diseases.