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 rho = 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.

The authors have declared no competing interest.

This study was funded by the Grant Agency of the Ministry of Health of the Czech Republic [NV17-31538A to M.G. and Pa.W.], the Grant Agency of the Czech Republic [20-16520Y to A.K. and 21-21736S to M.G.], and the Ministry of Education, Youth and Sports of the Czech Republic project NICR EXCELES [LX22NPO05102 to M.G.].

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Ethics Committee of the Institute for Clinical and Experimental Medicine and Thomayer Hospital with Multi-Center Competence waived ethical approval for this work (G16-06-25).

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