Ulcerative colitis

Last revised by Rohit Sharma on 16 May 2024

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) that not only predominantly affects the colon, but also has extra-intestinal manifestations.

Typically ulcerative colitis manifests in young adults (15-40 years of age) and is more prevalent in males but the onset of disease after age of 50 is also common 1,3,5

Ulcerative colitis is less prevalent in smokers than in non-smokers.

Clinically patients have chronic diarrhea (sometimes bloody) associated with tenesmus, pain, and fever 1. C-reactive protein levels are usually normal 6.

A combination of environmental and genetic factors are thought to play a role in the pathogenesis, although the condition remains idiopathic.

Unlike Crohn disease which is characteristically a transmural disease, ulcerative colitis is usually limited to the mucosa and submucosa 5

The diagnosis is often made with endoscopy, which also allows biopsy of any suspicious areas.

Several severity scoring systems exist. These include:

One of the most commonly used scoring systems. It is a composite of subscores from four categories, namely stool frequency, rectal bleeding, findings of flexible proctosigmoidoscopy/colonoscopy and physician’s global assessment. Total score ranges from 0-12 8.

Endoscopic component ranges from 0-3

  • 0: normal mucosa or inactive disease

  • 1: mild disease with evidence of mild friability, reduced vascular pattern, and mucosal erythema

  • 2: moderate disease with friability, erosions, complete loss of vascular pattern, and significant erythema

  • 3: ulceration and spontaneous bleeding

A newer endoscopic scoring system which includes assessment of vascular pattern, bleeding, and ulcers and excludes mucosal friability. In this system,

The vascular pattern is rated as 1-3

  • 1: normal

  • 2: patchy loss of vascular pattern

  • 3: complete loss of vascular pattern

Bleeding is characterized from 1-4

  • 1: none

  • 2: mucosal bleeding

  • 3: mild colonic luminal bleeding

  • 4: moderate or severe luminal bleeding

Erosions and ulcers are characterized from 1-4

  • 1: none

  • 2: erosions

  • 3: superficial ulceration

  • 4: deep ulcers 

Other classification systems include (used for inflammatory bowel disease in general)

Involvement of the rectum is almost always present (95%) 1, with the disease involving a variable length of the most distal colon, in continuity. The entire colon may be involved, in which case edema of the terminal ileum may also be present (so-called backwash ileitis). 

In very severe cases, the colon becomes atonic, with marked dilatation, worsened by bacterial overgrowth. This leads to toxic megacolon, which although uncommon, has a poor prognosis 13.

Non-specific findings, but may show evidence of mural thickening (more common), with thumbprinting also seen in more severe cases.

Double-contrast barium enema allows for exquisite detail of the colonic mucosa and also allows the bowel proximal to strictures to be assessed. It is however contraindicated if acute severe colitis is present due to the risk of perforation.

Mucosal inflammation leads to a granular appearance on the surface of the bowel. As inflammation increases, the bowel wall and haustra thicken.

Mucosal ulcers are undermined (button-shaped ulcers). When most of the mucosa has been lost, islands of mucosa remain giving it a pseudopolyp appearance.

In chronic cases, the bowel becomes featureless with the loss of normal haustral markings, luminal narrowing, and bowel shortening (lead pipe sign).

Small islands of residual mucosa can grow into thin worm-like structures (so-called filiform polyps)

Colorectal carcinoma in the setting of ulcerative colitis is more frequently sessile and may appear to be a simple stricture.

CT will reflect the same changes that are seen with a barium enema, with the additional advantage of being able to directly visualize the colonic wall, the terminal ileum and identify extra-colonic complications, such as perforation or abscess formation. It is important to note however that CT is insensitive to early mucosal disease 2

Inflammatory pseudopolyps may be seen if large enough, in well-distended bowel. In areas of mucosal denudation, abnormal thinning of the bowel may also be evident 2.

A cross-section of the inflamed and thickened bowel has a target appearance due to concentric rings of varying attenuation, also known as mural stratification 1,2.

In chronic cases, submucosal fat deposition is seen, particularly in the rectum (fat halo sign). Also in this region, extramural deposition of fat leads to thickening of the perirectal fat and widening of the presacral space 1,2.

Strictures are also common and are not all malignant. These are predominantly due to marked muscularis mucosae hypertrophy, which is also in part responsible for the lead pipe sign

Colorectal carcinoma is often sessile. Focal loss of mural stratification or excessive mural thickness (1.5 cm) should prompt endoscopic evaluation 2

Some segments of bowel may show pneumatosis cystoides intestinalis in some cases 10.

The current status of MRI in ulcerative colitis is that of a promising, non-invasive technique for imaging extent of more severe disease.

The most striking abnormalities in ulcerative colitis are colonic wall thickening and increased enhancement.

The median wall thickness in ulcerative colitis ranges from 4.7 to 9.8 mm. In general, the more severe the inflammation, the thicker the colonic wall. A colonic wall thickness <3 mm is usually considered as normal, 3-4 mm as a "gray zone," and >4 mm as pathological.

Use of diffusion-weighted imaging in the assessment of ulcerative colitis has been encouraging. One study, which compared the MRI with endoscopy, found that a b value of 800 s/mm2 was most accurate (cf. 400, 600 or 1000 s/mm2) at diagnosing active colitis, with a sensitivity of 93% and specificity of 79% 9.

Enhancement of the mucosa with absent or decreased enhancement of the submucosa produces a low signal intensity stripe - the so-called submucosal stripe.

Other features are the loss of haustral markingsbackwash ileitis, mild enhancement with no wall thickening, and increased signal intensity of the pericolonic fat.

Total colectomy is curative of both the intestinal symptoms and the potential risk of colorectal carcinoma. Medical therapy such as corticosteroids 18 is able to control colonic disease in some cases but does not remove the need for regular screening for malignancy.

Due to close surveillance patients with ulcerative colitis have a normal or even slightly improved survival compared to normal population 3. This is clearly not the case if the disease is not diagnosed or treatment not available. 

  • chronic disease is associated with a significantly elevated malignancy risk, of up to 0.5-1.0% per year after 10 years of the disease ref

  • 10-15% of cases initially presenting as ulcerative colitis later progress to Crohn disease ref

  • patients with ulcerative colitis may have a higher incidence of perianal disease than the general population 11

  • lower gastrointestinal tract hemorrhage

  • toxic megacolon

  • increased risk of thromboembolism 14

The most important differential diagnosis is Crohn disease (see Crohn disease vs ulcerative colitis). Otherwise, the differential includes other causes of colitis:

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