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Inflammatory bowel disease

mLpenguin

• 3 min read
Inflammatory bowel disease
Photo by Giorgio Trovato / Unsplash

Ulcerative Colitis (UC)

Location and Pattern

Ulcerative colitis has a very predictable pattern of involvement. It always begins in the rectum and spreads backward (proximally) through the colon in an unbroken, continuous fashion. UC never "skips" areas - if you have inflammation in the sigmoid colon, you'll definitely have it in the rectum.

Depth of Inflammation

UC is more superficial than Crohn's disease, affecting only the mucosa and submucosa (the inner layers) of the colon and rectum. This limited depth is actually good news when it comes to complications -> it's less likely to cause the deep problems we see with Crohn's disease (i.e, fistulas).

  • The immune response in UC is predominantly driven by Th2 and Th9 cells, with key players including interleukin-5 and interleukin-13.

Clinical Presentation

Patients with UC often start with nonbloody diarrhea that progresses to bloody diarrhea over time. One of the characteristic microscopic findings is the presence of crypt abscesses = small collections of inflammatory cells within the intestinal crypts.

An important long-term concern is the increased risk of colorectal cancer in patients with long-standing ulcerative colitis, making regular surveillance crucial.

Treatment Approach

Acute treatment: Corticosteroids like hydrocortisone are commonly used to control active inflammation.

Maintenance therapy: The goal is to keep the disease in remission using medications such as:

  • Mesalamine
  • Sulfasalazine
  • Immunomodulators like mercaptopurine
  • Anti-tumor necrosis factor-α medications

Curative option: Colectomy (surgical removal of the colon) can be curative since the disease is limited to the colon and rectum.

Crohn's Disease

Location and Pattern

Crohn's disease can affect any part of the gastrointestinal tract from mouth to anus, though it most commonly involves the terminal ileum (the last part of the small intestine).

What makes Crohn's particularly challenging is its discontinuous pattern of inflammation, often called "skip lesions." You might have severe inflammation in one area and completely normal tissue right next to it.

Depth of Inflammation

Crohn's is a transmural inflammatory condition, meaning it affects the entire thickness of the intestinal wall from the inner mucosa all the way to the outer serosa. This deep involvement is what leads to many of Crohn's more serious complications.

  • It's characterized by a dysregulated Th1/Th17-predominant response, with increased production of cytokines such as: Interferon-γ, Tumor necrosis factor-α (TNF-α), Interleukin-12/23
  • This immune activation leads to macrophage activation and immune cell recruitment throughout all layers of the intestinal wall, resulting in granuloma formation and deep ulceration.

Why the Patchy Distribution?

The heterogeneous distribution of immune responses in Crohn's disease is likely influenced by several factors:

  • Local variations in the gut microbiota
  • Genetic susceptibility (such as NOD2 gene variants)
  • Tissue-resident memory T cells that can drive localized, segmental immune activation

Complications

Because of its transmural nature, Crohn's disease can lead to serious complications such as:

  • Fistulas: Abnormal connections between different parts of the intestine or between the intestine and other organs
  • Abscesses: Collections of infected material
  • Strictures: Narrowing of the intestinal passage

Shared Features

Despite their differences, both conditions can cause extraintestinal manifestations that affect other parts of the body:

  • Uveitis: Eye inflammation
  • Arthritis
  • Aphthous Stomatitis (Canker Sores) - Painful, round or ovoid ulcers that appear on the inner lips, cheeks, underside of tongue, soft palate
  • Ankylosing spondylitis: Spine inflammation
  • Pyoderma gangrenosum: Severe skin ulcers
  • Primary sclerosing cholangitis: Bile duct inflammation
  • Toxic Megacolon

Toxic Megacolon

  • Definition: Severe, potentially life-threatening dilation of the colon (>6 cm) with systemic toxicity.
  • Common causes:
    • Inflammatory bowel disease (especially Ulcerative Colitis)
    • Infectious colitis (notably Clostridioides difficile infection)
  • Pathophysiology: Severe inflammation leads to paralysis of the colonic smooth muscle → dilatation → risk of perforation.
  • Clinical presentation:
    • Abdominal distension and pain
    • Fever
    • Tachycardia
    • Signs of systemic toxicity (hypotension, altered mental status)
    • Bloody diarrhea (especially in UC)
  • Diagnostic criteria:
    • Radiographic evidence of colonic dilation >6 cm (usually on abdominal X-ray)
    • Plus ≥3 of:
      • Fever
      • Tachycardia
      • Leukocytosis >10,500/mm³
      • Anemia
    • Plus ≥1 of:
      • Dehydration
      • Altered mental status
      • Electrolyte abnormalities
      • Hypotension
  • Complications: Perforation, sepsis, shock.
  • Management:
    • Medical: Bowel rest, IV fluids, broad-spectrum antibiotics, corticosteroids (for IBD flare), stop offending agents (e.g., antidiarrheals).
    • Surgical: Emergency colectomy if perforation or no improvement.
  • Avoid: Narcotics and anticholinergics (worsen motility).