Limited Validity of Mayo Endoscopic Subscore in Ulcerative Colitis with Concomitant Primary Sclerosing Cholangitis

Background and Aims Ulcerative colitis (UC) with concomitant primary sclerosing cholangitis (PSC) represents a distinct disease entity (PSC-UC). Mayo endoscopic subscore (MES) is a standard tool for assessing disease activity in UC but its relevance in PSC-UC remains unclear. Here, we sought to compare MES in a cohort of UC and PSC-UC patients and assess the accuracy using histological activity scoring (Nancy histological index; NHI). Methods MES was assessed in 30 PSC-UC and 29 UC adult patients during endoscopy. NHI and inflammation were evaluated in biopsies from the caecum, rectum, and terminal ileum. In addition, perinuclear anti-neutrophil cytoplasmic antibodies, fecal calprotectin, body mass index, and other relevant clinical characteristics were collected. Results The median MES and NHI were similar for UC patients (MES grade 2 and NHI grade 2 in the rectum), but were different for PSC-UC patients (MES grade 0 and NHI grade 2 in the caecum). There was a correlation between MES and NHI for UC patients (Spearman’s ρ = 0.40, p = 0.029), but not for PSC-UC patients. Histopathological examination revealed persistent microscopic inflammation in 88% of PSC-UC patients with MES grade 0 (46% of all PSC-UC patients). Moreover, MES overestimated the severity of active inflammation in another 11% of PSC-UC patients. Conclusion MES fails to identify microscopic signs of inflammation in the context of PSC-UC. This indicates that histological evaluation should become an integral part of the diagnostic and grading system in both PSC-UC and PSC.