Antimitochondrial Antibody-Negative Primary Biliary Cholangitis: A Diagnostic Challenge in a Sri Lankan Patient.

Primary biliary cholangitis (PBC) is a chronic autoimmune cholestatic liver disease characterized by progressive destruction of small intrahepatic bile ducts, in which antimitochondrial antibodies (AMA) are detected in the majority of patients and serve as a key diagnostic marker. A small subset of patients, however, remains AMA-negative, creating diagnostic uncertainty and potentially delaying treatment. We report the case of a 65-year-old woman who presented with progressive pruritus and fatigue and was found to have a predominantly cholestatic liver enzyme pattern. Extensive evaluation excluded extrahepatic biliary obstruction, viral hepatitis, and drug-induced liver injury. Despite a negative AMA test, a liver biopsy demonstrated portal inflammatory infiltrates with interface hepatitis and a prominent bile ductular reaction, establishing the diagnosis of AMA-negative PBC. The patient was commenced on ursodeoxycholic acid with partial symptomatic improvement. This case highlights the importance of maintaining clinical suspicion for PBC despite negative AMA and underscores the diagnostic value of liver biopsy in seronegative cases.