The term ulcerative colitis|segmental colitis|Crohn's disease (or diverticular colitis) is used to indicate the association between diverticulosis and chronic mucosal inflammation of the intestinal tract where diverticula are located (usually the sigmoid colon) [1,2]. The clinical presentation consists of rectal bleeding, occasionally left-sided abdominal pain and, less frequently, bowel alterations. The endoscopic features are those of sigmoiditis (erythema, congestion and contact bleeding) with rectal sparing.
The orifices of diverticula may or may not be involved. The histological changes are mostly similar to those detectable in inflammatory bowel disease (IBD): cryptic abscesses with crypt distortion, mononuclear cell infiltrate, lymphoid aggregation, epithelial cell sloughing  and sometimes granulomata [3,4]. On the whole, the histopathological features and rectal sparing mimick the picture of Crohn's disease rather than that of ulcerative colitis. In fact, in ulcerative colitis even when the rectum is endoscopically spared, histological involvement is always present .
Is ulcerative colitis|segmental colitis|Crohn's disease a distinct clinical entity or the fortuitous coexistence of sigmoid diverticulosis and IBD? Both diverticulosis and ulcerative colitis|segmental colitis|Crohn's disease usually affect elderly patients, especially men, and it is also known that IBD presents a second peak of incidence in the population over the age of 60 . The incidence of ulcerative colitis|segmental colitis|Crohn's disease is estimated to be 0.3–1.4% [1,2,7]. Conversely, in a series of 186 IBD patients admitted to our unit, coexistent sigmoid diverticulosis was detectable in 2.7% of cases . By and large, all the above figures are too small to allow definitive conclusions to be made in terms of epidemiology.
To add to the confusion, in about 10% of cases of ulcerative colitis|segmental colitis|Crohn's disease, inflammation subsequently spreads to the rectum, even if this was histologically normal initially, making it impossible to distinguish this condition from ulcerative colitis [1,2].
On the other hand, even when the rectum remains uninvolved and concomitant Crohn's colitis can be suspected, perianal disease is always absent [3,9]. In ulcerative colitis|segmental colitis|Crohn's disease, unlike in Crohn's colitis, symptoms such as nausea, vomiting, weight loss and fever are never present and laboratory findings are usually normal, the acute-phase reactants and/or white cell count being increased very rarely [7,9].
If ulcerative colitis|segmental colitis|Crohn's disease is an autonomous, though infrequent, intestinal disorder, what are the possible causes of local inflammation? A role for bacterial flora promoted by faecal stasis has been postulated . According to anecdotal reports [10,11], Aeromonas species might be involved, but this hypothesis still needs to be confirmed. Other postulated aetiological factors include: increased permeability to intraluminal antigens ; focal ischaemia due to impairment of local microcirculation ; and enhanced local production of nitric oxide and oxygen-reactive radicals [9,13].
Medical treatment of ulcerative colitis|segmental colitis|Crohn's disease is empirical and usually carried out, in addition to a high-fibre diet, by means of the same pharmacological agents employed in the treatment of IBD, i.e. sulfasalazine, mesalazine and occasionally antibiotics [1,2]. The majority of cases are responsive to such medications [1,2,14], corticosteroids being rarely required. Again, this differs from Crohn's disease, in which steroids and immunosuppressants are often necessary.
There are a few cases of patients with ulcerative colitis|segmental colitis|Crohn's disease requiring surgery [2,4,12] but, contrary to patients with Crohn's colitis, they rarely experience post-operative recurrences [4,15].
In conclusion, the very existence of ulcerative colitis|segmental colitis|Crohn's disease as a distinct intestinal disorder is supported by slim evidence. However, the possibility that chronic sigmoidal inflammation surrounding diverticula represents either an early or an atypical manifestation of IBD remains unconvincing, in spite of some similarities between the histological features of the two conditions. A differential diagnosis with Crohn's colitis is important in order to optimize the treatment and long-term management of the disease. To that purpose the diagnostic workout should include accurate evaluation of the small bowel by means of ileocolonoscopy with mucosal biopsies, radiological examination or both.
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