Identifying a therapeutic window of opportunity for people living with primary sclerosing cholangitis: Embryology and the overlap of inflammatory bowel disease with immune-mediated liver injury.

Primary sclerosing cholangitis (PSC) is a variably progressive, fibrosis-causing autoimmune disorder of the intrahepatic and extrahepatic bile ducts of unclear etiology. PSC is commonly (in 60%-90% of cases) associated with an inflammatory bowel disease (IBD) like PSC-IBD and less commonly with an autoimmune hepatitis (AIH) like PSC-AIH or AIH-overlap disorder. Hepatologists and Gastroenterologists often consider these combined conditions as distinctly different from the classical forms in isolation. Here, we review recent epidemiologic observations and highlight that PSC-IBD and PSC-AIH overlap appear to represent aspects of a common PSC clinico-pathological pathway and manifest in an age-of-presentation-dependent manner. Particularly from the pediatric experience, we hypothesize that all cases of PSC likely originate from a complex "Early PSC"-"IBD"-"AIH" overlap in which PSC defines the uniquely and variably associated "AIH" and "IBD" components along an individualized lifetime continuum. We speculate that a distinctly unique, "diverticular autoimmunity" against the embryonic cecal- and hepatic diverticulum-derived tissues may be the origin of this combined syndrome, where "AIH" and "IBD" variably commence then variably fade while PSC progresses with age. Our hypothesis provides an explanation for the age-dependent variation in the presentation and progression of PSC. This is critical for the optimal targeting of studies into PSC etiopathogenesis and emphasizes the concept of a "developmental window of opportunity for therapeutic mitigation" in what is currently recognized as an irreversible disease process. The discovery of such a window would be critically important for the targeting of interventions, both the administration of current therapies and therapeutic trial planning.

Immunotherapy withdrawal by step-down to mesalamine in pediatric patients with ulcerative colitis.

Objective: Parents and pediatric patients with ulcerative colitis (UC) who progressed to systemic immunotherapy are concerned about lifelong risks from such treatments. There is limited knowledge about withdrawal of such agents and step-down (SD) to enteral 5-aminosalicylic acid (mesalamine) before transitioning to adult care. Methods: We studied nine pediatric cases with moderate to severe UC who after a median of 2.18 years of clinical remission on systemic immunotherapy stepped down to oral mesalamine treatment. Results: Average follow-up time from SD was 3.49 years. Five patients (55.5%) had sustained remission (without any flare noted) after SD during follow-up. Sustained clinical remission was 88.9% (8/9) at 1 year, 87.5% (7/8) at 2 years, and 66.7% (4/6) at 3 years after SD. Out of those tested (one patient was not tested), 62.5% (5/8) had fecal calprotectin <50 µg/g. Four out of six patients examined (66.6%) had mucosal healing on post-SD colonoscopy. Conclusion: We propose that SD to mesalamine can be a reasonable therapeutic consideration for pediatric patients with UC before transitioning to adult gastroenterology care. Shared decision-making is important before such treatment changes.