A colonoscopy with visualisation of the entire colon and terminal ileum allows a correct differential diagnosis from CD in 85-90% of patients, but in 10-15% of patients, only a diagnosis of indeterminate colitis can be established . In severe disease, endoscopic examination must be limited (proctosigmoi-doscopy), with careful insufflation, due to high risk of perforation and toxic megacolon.
Endoscopic lesions change with inflammation degree. In mild disease, the mucosa is hyperaemic, with abnormal vascular pattern; in moderate disease, vascular pattern vanishes and the mucosa is friable, easily bleeding at instrument touch, with superficial ulcerations. Severe disease is characterised by spon taneously bleeding deep ulcerations, with mucopurulent exudate. Characteristically in UC, the rectum is involved at all times and, differently from CD, lesions are extended continuously from rectum to proximal colon. Therefore, inflammation can involve the sigma and rectum (proctosigmoiditis), extend to the splenic curve (left-side colitis) or affect the entire colon (extensive colitis). Before colonoscopy the patient's pharmacological history should be obtained because the use of medical enemas can normalise the rectal mucosae and induce erroneous CD diagnosis.
Ileal lesions are characteristic of CD and represent major macroscopic criteria to differentiate UC from CD. In 17% of patients with pancolitis, severe inflammation can induce incompetence of the ileocecal valve and consequent faecal reflux, causing inflammation (backwash ileitis). Generally, extension and severity of colitis are correlated to severity of ileum inflammation, even if 2% of backwash ileitis is associated to severe left-side colitis or mild extensive colitis. It seems that other pathogenetic factors are implicated to backwash ileitis (infections, bacterial overgrowth, reaction to drugs, etc.). Backwash ileitis does not seem to correlate with increased CRC development risk nor to higher incidence of complication after proctocolectomy with an ileal pouch .
In course of the first colonoscopy biopsies for histopathological definition of colitis type are necessary; in any cases, only biopsies can distinguish idio-pathic colitis from infectious colitis. Biopsies must be taken from inflamed mucosae, healthy mucosae and ileum since real UC extension and existence of microscopic inflammation must be evaluated because therapy and prognosis can change accordingly. A new approach to microscopic inflammation is confocal endoscopy (see below), which allows targeted biopsies.
During silent disease (remission phase), haustrae are reduced and the colon is tube like; characteristic lesions are pale and sometimes granulose mucosae (atrophy) is apparent and there is a loss of vascular pattern and presence of pseudopolyps. The so-called inflammatory polyps are present in acute and quiescent disease and are composed of regenerating mucosae and inflammatory cells without dysplastic epithelium. Therefore, they do not degenerate to CRC. The use of A video capsule is very limited in UC. It can play a marginal role in indeterminate colitis, showing unknown lesions in the small intestine that can contribute to a diagnosis of CD .
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