28. INFLAMMATORY BOWEL DISEASE

Introduction

Inflammatory Bowel Disease (IBD) is a long-term inflammatory condition of the gastrointestinal tract. It happens because of an abnormal and uncontrolled immune response to the normal bacteria (microflora) present in the intestine. IBD mainly includes two conditions: Crohn’s Disease (CD) and Ulcerative Colitis (UC).

Ulcerative Colitis

UC causes continuous inflammation and ulcers in the inner lining of the large intestine (colon) and rectum. It usually starts in the rectum and spreads upward to the sigmoid, descending and transverse colon. In some patients, colonic contents may flow back into the terminal ileum, causing a condition called backwash ileitis.

Crohn’s Disease

Crohn’s disease can affect any part of the GI tract but most commonly involves the last 15–25 cm of the terminal ileum, extending into the caecum or ascending colon. Both UC and Crohn’s disease may cause severe diarrhea, abdominal pain, fatigue and weight loss.

Epidemiology

  • IBD is most common in Western countries and northern latitudes.
  • Highest rates are reported in Scandinavia, Great Britain and North America.
  • Crohn’s Disease incidence: 3.6–8.8 per 100,000 people; prevalence: 20–40 per 100,000.
  • Ulcerative Colitis incidence: 3–15 per 100,000; prevalence: 80–120 per 100,000.
  • Both genders are equally affected; CD slightly more common in women, UC slightly more common in men.
  • IBD shows two peak age groups: 20–40 years and 60–80 years.
  • Ashkenazi Jews have 4–5 times higher risk; Asians and Blacks have lower risk.

Etiology (Causes)

IBD is idiopathic, meaning exact cause is unknown, but multiple factors contribute.

1) Immunological Factors

In IBD, the immune system reacts abnormally to gut bacteria, causing chronic inflammation of the GI tract.

2) Genetic Factors

  • First-degree relatives have 3–20 times higher risk.
  • Monozygotic twins: 50% chance (Crohn’s ~60%; UC ~6%).
  • Genes affecting epithelial barrier function play a role.

3) Exogenous Factors

  • Microbial factors: Bacteria, viruses, protozoa and fungi may contribute, though evidence is unclear.
  • Psychosocial factors: Stress, emotional trauma, and personality traits may worsen symptoms.
  • Smoking: Strongly linked to Crohn’s disease.
  • Oral contraceptives: Long-term use may increase Crohn’s disease risk.

Pathophysiology

The appearance and location of lesions differ between Crohn’s Disease and Ulcerative Colitis.

Crohn’s Disease Pathophysiology

  • Inflammation is transmural (involves entire bowel wall).
  • Lesions appear in patches (skip lesions) with normal tissue between them.
  • Starts with granuloma formation, then ulceration and abscess development.
  • Fistulas may form between intestine and bladder, vagina or rectum.
  • Repeated inflammation leads to cobblestone appearance, strictures and bowel obstruction.
  • Non-caseating granulomas may appear in lymph nodes, liver, peritoneum or bowel layers.

Ulcerative Colitis Pathophysiology

  • UC affects only the mucosal layer of the colon.
  • Classic lesion: crypt abscess filled with pus and necrotic debris.
  • Lesions ulcerate and bleed during flare-ups and heal with scarring.

Immune Mechanisms

A healthy gut normally tolerates food antigens and friendly gut bacteria. This tolerance is mediated by CD4+ T cells releasing anti-inflammatory cytokines (IL-10, TGF-β).

In IBD, this immune suppression fails, leading to uncontrolled inflammation.

Types of CD4+ T Cells in IBD

  • TH1 Cells: Secrete IFN-γ and TNF → cause transmural granulomatous inflammation (Crohn’s).
  • TH2 Cells: Secrete IL-4, IL-5, IL-13 → cause superficial mucosal inflammation (Ulcerative colitis).

Signs & Symptoms

Ulcerative Colitis

UC symptoms vary greatly from mild to severe.

  • Mild disease: <4 stools/day with or without blood; no systemic symptoms; normal ESR.
  • Moderate disease: >4 stools/day, mild systemic symptoms.
  • Severe disease: >6 stools/day with blood, fever, tachycardia, anemia or ESR >30.
  • Intermittent flare-ups with periods of remission.

Crohn’s Disease

  • Symptoms vary widely.
  • Diarrhea, abdominal pain and weight loss are common.
  • Perianal lesions such as fistulas or abscesses may be present.
  • Course marked by periods of remission and exacerbation.
  • CDAI (Crohn Disease Activity Index) helps determine disease severity.

Diagnosis

Diagnosis involves medical history, physical exam, lab tests and imaging.

General Examination

  • Paleness (anemia)
  • Abdominal tenderness
  • Skin rash
  • Joint swelling
  • Mouth ulcers

Blood Tests

  • Low RBC count → anemia
  • High WBC count → inflammation or infection
  • Antibody tests may help differentiate Crohn’s from UC

Stool Test

Used to rule out infections and other GI conditions.

Imaging Tests

  • Upper GI series to examine upper digestive tract.
  • Upper GI endoscopy to view the esophagus, stomach and duodenum.
  • Colonoscopy (preferred) for complete colon examination.
  • Flexible sigmoidoscopy for lower colon.
  • Abdominal X-ray to detect obstruction.
  • Barium enema (rarely used now) to examine colon structure.
  • CT scan to detect disease and complications.
  • MRI to identify fistulas, sinus tracts and abscesses.

Detailed Notes:

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