Fibrosis in ulcerative colitis is directly linked to severity and chronicity of mucosal inflammation

Abstract

Background: Fibrosis in ulcerative colitis has remained largely unexplored despite its clinical implications.

Aims: This cross-sectional study was aimed at characterising the presence, anatomical location and degree of ulcerative colitis-associated fibrosis and its possible link to clinical parameters.

Methods: Seven hundred and six individual tissue cross-sections derived every 10 cm along the length of 89 consecutive Ulcerative colitis colectomy specimens were examined and compared to Crohn's disease colitis, diverticular disease and uninvolved areas from colorectal cancer patients. Degree of inflammation, fibrosis and morphometric measurements of all layers of the intestinal wall were evaluated. Three gastrointestinal pathologists independently assessed colon sections stained with haematoxylin and eosin, Masson trichrome and Sirius red. Clinical data were collected prospectively.

Results: Submucosal fibrosis was detected in 100% of ulcerative colitis colectomy specimens, but only in areas affected by inflammation. Submucosal fibrosis was associated with the severity of intestinal inflammation (Spearman correlations rho (95% confidence interval): 0.58 (P < 0.001) and histopathological changes of chronic mucosal injury, but not active inflammation. Colectomy for refractory disease rather than presence of dysplasia was associated with increased fibrosis and a thicker muscularis mucosae, whereas a thinner muscularis mucosae was associated with anti-tumour necrosis factor therapy. No feature on endoscopic mucosal biopsies could predict the underlying amount of fibrosis or the thickness of the muscularis mucosae.

Conclusions: A significant degree of fibrosis and muscularis mucosae thickening should be considered as common complications of chronic progressive ulcerative colitis. These features may have clinical consequences such as motility abnormalities and increased wall stiffness.

Figure 1. Grading of inflammation

Inflammation was graded based on the Geboes score , and separated into active inflammation and chronic mucosal injury. Green indicates chronic mucosal injury and red indicates active inflammation.

Figure 2. Measurement method for whole thickness intestinal cross sections

Specific measurements were determined on hematoxylin and eosin stained sections and included a full-thickness measurement, as well as a measurement of each histologic intestinal wall layer (mucosa, muscularis mucosae, submucosa, muscularis propria). These measurements were performed in two areas per slide, corresponding to the highest (A) and lowest (B) thickness of submucosa present. Arrow colors: black-full thickness; blue-muscularis propria; green-submucosa; red-mucosa

Figure 3. Degree of submucosal fibrosis in Ulcerative colitis

Correlation between Sirius red vs. Hematoxylin & Eosin (A) and Masson Trichrome (B)

Figure 4. Fibrosis burden in involved and non-involved areas in Ulcerative colitis

(A) Comparison of the degree of fibrosis on hematoxylin & eosin stain between involved and non-involved segments of Ulcerative colitis colon (n=706). (B) Comparison of the degree of fibrosis on Masson trichrome stain between involved and non-involved segments of the Ulcerative colitis colon (left panel: entire cohort (n=706); right panel: within the same patient (n=24)). (C) Comparison of the degree of muscularis mucosae thickening between involved and non-involved segments of Ulcerative colitis colon (entire cohort n=706 in bar graph on the left, involved and non-involved segments within the same patient n=24 in middle). The thickness of the entire intestinal wall remained unchanged (n=706 in bar graph on right). (D) Longitudinal plots depicting the variation for the degree of fibrosis (as evaluated by Masson trichrome, left side) and degree of muscularis mucosae thickening (right side) only in the areas affected by inflammation. The percent of segments with a particular degree of fibrosis (0–100%) is depicted. (E) Representative examples of hematoxylin & eosin as well as Masson trichrome stained colon sections showing involved and non-involved segments.

Figure 4. Fibrosis burden in involved and non-involved areas in Ulcerative colitis

(A) Comparison of the degree of fibrosis on hematoxylin & eosin stain between involved and non-involved segments of Ulcerative colitis colon (n=706). (B) Comparison of the degree of fibrosis on Masson trichrome stain between involved and non-involved segments of the Ulcerative colitis colon (left panel: entire cohort (n=706); right panel: within the same patient (n=24)). (C) Comparison of the degree of muscularis mucosae thickening between involved and non-involved segments of Ulcerative colitis colon (entire cohort n=706 in bar graph on the left, involved and non-involved segments within the same patient n=24 in middle). The thickness of the entire intestinal wall remained unchanged (n=706 in bar graph on right). (D) Longitudinal plots depicting the variation for the degree of fibrosis (as evaluated by Masson trichrome, left side) and degree of muscularis mucosae thickening (right side) only in the areas affected by inflammation. The percent of segments with a particular degree of fibrosis (0–100%) is depicted. (E) Representative examples of hematoxylin & eosin as well as Masson trichrome stained colon sections showing involved and non-involved segments.

Figure 5. Fibrosis and muscularis mucosae thickness in Ulcerative colitis colonic segments grouped according to active inflammation and chronic mucosal injury

(A) Bar graphs show segments with no inflammation, active inflammation only, chronic mucosal injury only or both active inflammation and chronic mucosal injury linked to degree of fibrosis (0–100%) as measured by hematoxylin & eosin (left) and Masson trichrome (right). (B) Heat map for distribution of grades of active inflammation, chronic mucosal injury and degrees of fibrosis along the colon. Segments were ordered from distal to proximal. The grades of active inflammation, chronic mucosal injury and degree of fibrosis were plotted as the signal with red indicating a high and green indicating a low severity. The orange colored segments in the proximal area for active inflammation represent increased active inflammation, but no chronic mucosal changes due to cecal patches. (C) Box plots showing segments with no inflammation, active inflammation only (active), chronic mucosal injury only (chronic) or both active inflammation and chronic mucosal injury (active and chronic) linked to the thickness of the muscularis mucosae.

Figure 6. Correlation between degree of intestinal inflammation and submucosal fibrosis or muscularis mucosae thickness

(A) Hematoxylin & eosin stain and numerical Geboes score; (B) Masson trichrome and numerical Geboes score; (C) Thickness of the muscularis mucosae and numerical Geboes score. The different histologic findings are color coded. The size of the circles represents the number of patients per condition.