"From Cholestasis to Interface Hepatitis: A Rare Case of Primary Sclerosing Cholangitis-Autoimmune Hepatitis Overlap in a 20-Year-Old Male".

INTRODUCTION: Overlap syndrome refers to the coexistence of more than one immune-mediated liver disease in a single patient. Primary sclerosing cholangitis-autoimmune hepatitis (PSC-AIH) overlap is a rare but clinically important entity, as delayed recognition may lead to progressive liver injury, cirrhosis, and liver failure. Differentiating this condition from isolated PSC or AIH remains challenging due to overlapping clinical, biochemical, and radiological features. CASE PRESENTATION: A 20-year-old male presented with progressive jaundice, pruritus, acholic stools, and dark urine for one month. Laboratory evaluation revealed marked cholestasis with significantly elevated alkaline phosphatase and transaminases, hyperbilirubinemia, and coagulopathy, while viral and metabolic causes were excluded. Magnetic resonance cholangiopancreatography demonstrated characteristic intrahepatic biliary duct irregularities consistent with primary sclerosing cholangitis. However, disproportionately elevated alanine aminotransferase and serum immunoglobulin G levels prompted further evaluation. Liver biopsy revealed features of both diseases, including interface hepatitis with chronic portal inflammation and plasma cell infiltration, along with bile duct injury, ductopenia, and onion-skin fibrosis. Based on histology and diagnostic scoring, a diagnosis of PSC-AIH overlap syndrome was established. The patient was treated with ursodeoxycholic acid, corticosteroids, and azathioprine, resulting in marked clinical and biochemical improvement on follow-up. CONCLUSION: This case highlights the importance of considering PSC-AIH overlap syndrome in young patients with cholestatic liver disease and unexpectedly elevated transaminases or immunoglobulin G levels. Early recognition and combined immunosuppressive and supportive therapy can lead to favorable outcomes and may prevent irreversible liver damage.