What is colitis, how does it cause bowel strictures, and how does it differ from ulcerative colitis?

Understanding Colitis and Bowel Strictures vs. Ulcerative Colitis

Colitis is a broad term for inflammation of the colon that can result from multiple causes, while ulcerative colitis is a specific type of chronic inflammatory bowel disease with distinct pathological features—the key difference being that ulcerative colitis causes continuous, superficial mucosal inflammation starting from the rectum, whereas other forms of colitis (particularly Crohn's colitis) can cause transmural inflammation with skip lesions that lead to fibrotic strictures through repeated cycles of inflammation and repair.

What is Colitis?

Colitis refers to inflammation of the colon from various etiologies including:

• Inflammatory bowel disease (IBD): Ulcerative colitis and Crohn's colitis
• Infectious causes: Bacterial, viral, or parasitic
• Ischemic colitis: Due to reduced blood flow
• Microscopic colitis: Lymphocytic or collagenous subtypes

The term itself is descriptive rather than diagnostic—it indicates colonic inflammation but doesn't specify the underlying cause.

How Colitis Causes Bowel Strictures (Obstruction)

Stricture formation occurs primarily in Crohn's disease affecting the colon, not typically in ulcerative colitis. 1

Mechanism of Stricture Development:

Crohn's disease strictures result from complex interactions between inflammatory cells, cytokines, mesenchymal cells, and enteric flora, leading to variable degrees of luminal narrowing. 1 The process involves:

• Transmural inflammation: Unlike UC, Crohn's causes full-thickness bowel wall inflammation
• Repeated injury-repair cycles: Chronic inflammation triggers fibroblast activation
• Fibrosis deposition: Collagen accumulates in all layers of the bowel wall
• Smooth muscle hypertrophy: The muscular layer thickens in response to chronic inflammation
• Progressive luminal narrowing: Fixed stenosis develops over time

The majority of Crohn's disease strictures contain both inflammatory and fibrotic components due to repeated inflammation and reparative damage. 1 This mixed pathology explains why some strictures respond partially to anti-inflammatory therapy while others require surgical intervention.

Clinical Presentation:

Strictures manifest as:

• Bowel obstruction symptoms: Cramping abdominal pain, distension, nausea, vomiting
• Radiologic findings: Luminal narrowing with proximal bowel dilation (typically >3 cm) 1
• Progressive symptoms: Worsening over time as fibrosis accumulates

Surgery is mandatory for symptomatic intestinal strictures that do not respond to medical therapy and are not amenable to endoscopic dilatation in Crohn's disease. 2

Key Differences Between General Colitis and Ulcerative Colitis

Anatomic Distribution:

Ulcerative Colitis:

• Always begins in the rectum and extends proximally in a continuous pattern 3, 4
• Diffuse, uninterrupted inflammation without skip lesions
• Sharp transition between diseased and normal mucosa
• Can have unusual patterns: cecal patch (periappendiceal inflammation in left-sided disease), rectal sparing (with topical therapy), backwash ileitis (20% with extensive colitis) 3

Crohn's Colitis:

• May spare the rectum and has patchy, discontinuous distribution 4
• Skip lesions are characteristic
• Can affect any part of the GI tract from mouth to anus

Depth of Inflammation:

Ulcerative Colitis:

• Limited to mucosa and occasionally superficial submucosa 3, 4
• Inflammation is proportionate—higher cellularity in mucosa than submucosa 3
• Fibrosis, when present, is restricted to mucosa/submucosa 3

Crohn's Colitis:

• Transmural involvement affecting all layers of the intestinal wall 4
• Can extend through muscularis propria to serosa
• Serositis is present (absent in UC except fulminant colitis) 3

Microscopic Features:

Ulcerative Colitis:

• Diffuse, continuous crypt architectural distortion (57-100% of cases) 3
• Crypt branching and atrophy
• Basal plasmacytosis (plasma cells between crypt bases and muscularis mucosae)—present in 63% of UC vs 6% of infectious colitis 3
• Crypt abscesses common (41% vs 19% in Crohn's) 3
• Mucin depletion pronounced
• No granulomas (except with ruptured crypts) 3
• Paneth cell metaplasia present

Crohn's Colitis:

• Focal, discontinuous inflammation
• Granulomas and giant cells present in majority of cases 3, 4
• Transmural lymphoid aggregates
• Neuronal hyperplasia common
• Muscular hypertrophy present
• Pyloric gland metaplasia

Stricture Formation:

Ulcerative Colitis:

• Strictures are uncommon (3.2-11.2% of cases) 3
• When present, occur in longstanding disease with tissue repair and fibrosis
• Incidence is only 3.6% overall, with cumulative probability of 1% at 5 years and 2.3% at 10 years 5
• High malignancy risk: 42.9% of UC strictures harbor dysplasia, and 33.3% develop colorectal cancer 5
• Risk factors: Age >40 years at diagnosis (Montreal A3), steroid use 5, 6
• Protective factor: Mesalamine use, biologic agents like vedolizumab 5, 6

Crohn's Colitis:

• Strictures are common and a major complication 2, 7
• Result from transmural fibrosis and smooth muscle hypertrophy
• Symptomatic strictures occur more often than in UC 7
• Any colorectal stricture should be assessed with endoscopic biopsies to ensure absence of malignancy 2

Perianal Disease:

Ulcerative Colitis:

• Perianal fistulas and ulcers are rare 4

Crohn's Colitis:

• Perianal fistulas and ulcers are common 4
• About one-quarter present at or before Crohn's diagnosis 1

Clinical Implications:

Ulcerative Colitis:

• More frequent response to medical management 4
• Total colectomy with ileostomy results in cure 4
• Colorectal cancer risk is significant, especially with strictures
• Growth failure less severe than Crohn's 4

Crohn's Colitis:

• May respond less frequently to medical therapy
• Surgery provides remission but disease likely to recur, often in small intestine 4
• Severe growth failure that may precede intestinal symptoms by months to years 4
• Requires lifelong monitoring even after surgery

Critical Clinical Pitfalls:

1. Never assume a colonic stricture in UC is benign: 42.9% harbor dysplasia 5. All UC strictures require thorough endoscopic assessment with biopsies and discussion in multidisciplinary team 8.

2. Don't confuse stricture definitions: Endoscopists define strictures by inability to traverse with scope, while radiologists require proximal dilation >3 cm 1. Both perspectives matter clinically.

3. Recognize that most Crohn's strictures are mixed: They contain both inflammatory and fibrotic components 1. Pure "inflammatory" vs "fibrotic" strictures are rare—no imaging technique is sufficiently accurate to quantify fibrosis 8.

4. In UC patients with strictures: Consider earlier biologic therapy, especially in those ≥40 years or with extraintestinal manifestations 6. These patients have worse long-term outcomes including higher surgery rates (37.6% at 10 years) 6.

5. Backwash ileitis in UC can mimic Crohn's terminal ileitis: Occurs in ~20% of extensive UC 3. Distinction requires careful assessment of other features.