The interrelationship between small Duct PSC and Large Duct PSC: diagnostic challenges, genetic insights, and prognostic implications; a narrative review

Abstract

PURPOSE OF REVIEW To understand the pathogenesis, genetic associations, and the relationship of small-duct primary sclerosing cholangitis (sdPSC) with large-duct primary sclerosing cholangitis (ldPSC) and with IBD. Can early detection of sdPSC influence the progression to more severe forms and improve patient outcomes? RECENT FINDINGS sdPSC affects intra-hepatic ducts and lacks the cholangiographic features of ldPSC. Diagnosis of sdPSC requires a liver biopsy. sdPSC is less common and has a more favourable prognosis. While both sdPSC and ldPSC share histopathological similarities, sdPSC changes are subtle. Genetically, sdPSC is linked to HLA-DRB113:01 and B08, whereas ldPSC is more associated with HLA-B08. About 25% of sdPSC cases may progress to ldPSC. sdPSC has a lower risk of colorectal cancer and cholangiocarcinoma. SUMMARY sdPSC is genetically different from ldPSC, but the histology appears similar. Differentiating between sdPSC and ldPSC is essential for management, with annual colonoscopy recommended for PSC-IBD patients. sdPSC patients with concomitant IBD might represent precursors to classic large duct PSC. In contrast, those without IBD may represent a different cholangiopathy, warranting further investigation.