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 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.

Learning Points: Autoimmune thyroid disease in a patient should raise suspicion for autoimmune polyglandular syndrome type 3 (APS-3) and other potential autoimmune conditions.If APS-3 is diagnosed, further classification is recommended, along with a thorough search for additional autoimmune diseases.APS-3 serves as a framework for the differential diagnosis of autoimmune diseases.