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Histopathology of segmental colitis associated with diverticulosis resembles inflammatory bowel diseases.

To the Editor: Segmental colitis associated with diverticulosis (SCAD) is a chronic colitis that is confined to the colonic segment containing diverticula.1 By definition, the rectum and proximal colon are spared from inflammation,1 and endoscopic inflammation is confined to the interdiverticular mucosa with sparing of diverticular orifices.2 Although the prevalence of SCAD is increasing,3 it is still unclear if SCAD is a form of chronic intestinal inflammation occurring by chance close to the diverticula or a truly autonomous clinical entity.4 This is particularly true when we assess histology of SCAD. Among studies dealing with the histology of SCAD, nearly all have remarked its close morphologic similarities to inflammatory bowel disease in most if not all cases.1,5 In particular, cryptitis, increase of mononuclear inflammatory cells in lamina propria, and basal lymphoid aggregates are the main microscopic findings, as reported by some studies.2,6 However, a quantitative comparison of the histopathologic findings between inflammatory bowel disease and SCAD has not been performed yet. In the present study we compared the histopathology characteristics of SCAD with those of ulcerative colitis (UC), to assess what are the histopathology similarities and differences between these 2 different categories of chronic colonic diseases. Eight patients (3 males, 5 females; median age, 63; range, 57 to 69 y) with SCAD were compared with 4 active UC patients (1 male, 3 females; median age, 23; range, 21 to 59 y). All UC patients were affected by mild to moderate disease.7 Only patients at the first diagnosis of SCAD and UC were studied, to avoid influence of drugs on colonic histology. Patients with a previous endoscopic or radiologic diagnosis of diverticular disease, patients with drug-induced colitis, with endoscopic evidence of either colonic polyps (including hyperplastic polyps), or colon cancer were excluded. Other exclusion criteria were: personal or family history of colonic neoplasia, inflammatory bowel disease, and large bowel resection. SCAD was classified according to the recent endoscopic definition of SCAD.2 To compare histopathology characteristics, biopsy samples from sigmoid region were reviewed (both in SCAD and in IBD patients). Two expert histopathologists (F.M. and G.G.) reviewed the biopsy samples, blinded as far as endoscopic and clinical data of the patients were concerned. Hematoxylin and eosin staining was performed to assess histology. Ten histologic parameters were assessed according to the European Crohn’s and Colitis Organisation Consensus on the histopathology of IBD8: epithelium (normal, severe damage, complete destruction/absence); mucin depletion (presence, reduction, absence); intraepithelial lymphocytes (normal number or increased number); inflammatory infiltrate (both in the lamina propria and epithelium), subdivided according to the type of inflammatory cells: L=lymphocytes, P=plasma cells, N=neutrophils, E= eosinophils, H=histioid cells; blood vessels (dilation); edema (generally subepithelial); fibrosis (generally deep, that may indicate an older disease); hemorrhage—erosions. Lesions were graded from 0, when absent, to 5, when extremely severe (eg, when inflammatory infiltrate destroys crypts). The concordance between the 2 histopathologists in assessing histologic parameters was excellent (weighted k=0.90). All parameters assessed were altered in both SCAD and UC. However, cytoarchitectural structure was severely altered in all UC patients and in no patients with SCAD. Significant difference also occurred with respect to mucin depletion (P= 0.015) and erosion (P=0.026) (Fig. 1). Inflammatory infiltrate, subdivided according to the type of inflammatory cells, showed significant difference with respect to histioid cells (P=0.006), lymphocytes (P=0.033), and plasma cells (P=0.041) (Fig. 2). This study found for the first time that all IBD histopathology parameters may be detected in SCAD too, even if UC histopathology seems to be more severe. Therefore, the present study seems to confirm that SCAD FIGURE 1. Comparison of the histologic parameters. IEL indicates intraepithelial lymphocytes; SCAD, segmental colitis associated with diverticulosis; UC, ulcerative colitis. Bars represent median.