Disorders of the intestines

Pathological Findings in Inflammatory Bowel Disease (IBD)

Types of IBD

Two major types of Inflammatory Bowel Disease (IBD) are:

  1. Crohn's Disease

    • Can affect any part along the gastrointestinal tract (GI), but is most commonly found in the ileum.

  2. Ulcerative Colitis

    • Primarily affects the colon and usually starts at the rectum.

Characteristics and Consequences of Malabsorption Disorders

Inflammatory Bowel Disease is characterized by chronic inflammation of the intestines in genetically susceptible individuals. The underlying pathogenesis of IBD is thought to involve an interaction between the intestinal microbiota and an abnormal host immune response. Both types of IBD go through periods of exacerbation followed by periods of remission.

Important Distinctions

  • IBD is distinct from Irritable Bowel Syndrome (IBS).

  • The primary distinction between Crohn's disease and ulcerative colitis involves the affected location and the depth of the GI tract wall:

    • Crohn's Disease: Involves all layers of the GI wall deeply.

    • Ulcerative Colitis: Involves only the superficial layers (mucosa and submucosa).

Both conditions are linked to an increased risk of colorectal cancer due to chronic inflammation.

Epidemiology and Risk Factors

  • The estimated incidence of IBD in the Australian population is approximately 653 per 100,000.

  • Risk factors for developing IBD include:

    • Family history of IBD.

    • Living in an industrialized country.

    • Dietary factors: Low fruit and fiber intake, high fat intake.

  • The onset is most common in individuals during their teens to 30s, with a secondary peak after age 60.

Clinical Manifestations; Comparison of Crohn's Disease and Ulcerative Colitis

Diarrhea

  • Crohn's Disease: Common and often presents as a "cobblestone" appearance in the intestines.

  • Ulcerative Colitis: Rare in presentation.

Depth of Involvement

  • Crohn's Disease: Affects deep layers of the GI wall.

  • Ulcerative Colitis: Generally superficial (mucosa and submucosa).

Types of Lesions

  • Crohn's Disease: Characterized by "skip lesions" (areas of inflammation surrounded by healthy tissue).

  • Ulcerative Colitis: Typically presents with continuous lesions without "skips".

Abdominal Pain

  • Crohn's Disease: Commonly associated with cramping.

  • Ulcerative Colitis: Commonly presents as constant pain.

Weight Loss

  • Crohn's Disease: Common due to malabsorption of nutrients, particularly from the small intestines.

  • Ulcerative Colitis: Rare.

Rectal Bleeding

  • Crohn's Disease: Uncommon.

  • Ulcerative Colitis: Common.

Malabsorption and Nutrient Deficiency

  • Crohn's Disease: Common due to extensive involvement of the small intestine.

  • Ulcerative Colitis: Minimal.

Complications in IBD

Cancer Risk

  • Both Conditions: Increased risk of colorectal cancer due to chronic inflammation.

Infections

  • Both Crohn’s disease and ulcerative colitis can present with an increased risk of C. difficile Infection.

Perforation

  • Crohn's Disease: Common, typically due to the depth of damage.

  • Ulcerative Colitis: Common, particularly due to toxic colon effects.

Fistula Formation

  • Crohn's Disease: Common, especially when deep lesions occur.

  • Ulcerative Colitis: Rare.

Stricture Formation

  • Crohn's Disease: Common.

  • Ulcerative Colitis: Uncommon.

Systemic Manifestations

Although inflammation primarily occurs in the GI tract, systemic manifestations can arise due to persistent circulating pro-inflammatory cytokines.

Coeliac Disease

Coeliac disease is an immune-mediated condition that manifests with structural changes to the intestinal lining due to an immune reaction to gluten, an allergenic protein found in wheat, barley, and rye. It predominantly affects genetically predisposed individuals and may also be referred to as celiac sprue.

Clinical Manifestations

The clinical signs and symptoms of coeliac disease vary significantly among individuals, leading to difficulties in diagnosis. The main manifestations include:

  • Flattening or loss of intestinal villi observed during procedures like colonoscopy.

Colonoscopy

A colonoscopy is a medical procedure for visualizing parts of the distal gastrointestinal tract. Notable abnormalities, such as polyps, may be detected and removed during this procedure. In cases of coeliac disease, histopathological examination may reveal changes in the intestinal lining, such as loss of villi.

Pathogenesis of Coeliac Disease

The pathogenesis of Coeliac Disease is driven by a cell-mediated immune response triggered by gluten, resulting in damage to the intestinal epithelial cells. Over time, this leads to mucosal changes and impaired nutrient absorption in the small intestine. Patients commonly present with nutrient deficiencies, including iron-deficiency anemia. Individuals with coeliac disease have specific human leukocyte antigen (HLA) types, specifically HLA-DQ2 or HLA-DQ8, which are essential for the development of this condition. Current management includes adhering to a strict gluten-free diet and accessing support services like Coeliac Australia.

Gastrointestinal Tumours

Tumours in the gastrointestinal tract can be classified into benign (e.g., adenomas) or malignant (e.g., cancers), with colorectal cancers being the most commonly diagnosed gastrointestinal cancers, followed by cancers of the pancreas, stomach, liver, and esophagus.

Screening Programs

In efforts to mitigate morbidity and mortality related to colorectal cancers, the National Bowel Screening Program was initiated in 2006 for Australians aged 50-74. Screening enables the detection of cancers or polyps, often well before symptomatic presentations occur.

Polyps

Polyps are small tissue growths that begin as elevations in the mucosal lining and can occur throughout the gastrointestinal tract, though they are most frequently found in the colon and rectum. They can be classified into:

  • Non-neoplastic polyps.

  • Neoplastic polyps (adenomas): These polyps exhibit epithelial dysplasia and are precursors to the majority of colorectal cancers.

Colorectal Cancers

Approximately 90% of colorectal cancers are adenocarcinomas, a term denoting cancers originating from the glandular epithelium. The risk of developing colorectal cancer escalates in individuals over 50 years and those with existing polyps. Several modifiable risk factors exist which may aid in the prevention of colorectal cancers, including physical activity and dietary choices.

Dietary Factors

  1. Protective Factors:

    • Dietary fibres enhance stool bulk and support normal intestinal functions.

    • Foods such as vegetables, fruits, and garlic provide protective benefits.

  2. Risk Factors:

    • High intake of red meat can foster bacterial growth in the colon, potentially leading to carcinogenic compounds.

    • Diets high in fats, alcohol, and processed sugars may correlate with a heightened risk of colorectal cancers.

Pathophysiology of Colorectal Cancers

Most colorectal cancers develop from neoplastic polyps through a slow progression. Neoplastic polyps often display dysplastic changes and may further mutate into cancers in the presence of carcinogens. Colorectal cancers can invade and metastasize, primarily to the liver and lungs, taking advantage of the rich lymphatic network in the gastrointestinal tract.

Clinical Manifestations of Colorectal Cancers

Symptoms and signs of colorectal cancers depend significantly on the tumor's location and size within the GI tract. Common signs may include bleeding, abdominal pain, and changes in bowel habits. Early manifestations might mimic other inflammatory bowel conditions, such as Crohn's disease.

Cancer Staging System

The TNM system is employed for staging colorectal cancers, which can be consulted for detailed information regarding the staging processes.

Malabsorption and Maldigestion

Definitions

  • Malabsorption: Results from damage to the intestinal mucosa where normal nutrient absorption across the intestinal tract becomes impaired.

  • Maldigestion: Occurs when the digestion of nutrients is compromised, such as in cases of lactose intolerance, which is due to insufficient levels of the enzyme lactase necessary to digest lactose.

Common Maldigestive Disorders

  • Insufficient bile salts leading to impaired fat digestion.

  • Pancreatic insufficiency affecting overall nutrient digestion.

Complications from Malabsorption and Maldigestion

This can lead to various complications, including nutritional deficiencies, diarrhea, and abdominal pain that may arise due to insufficient nutrient absorption.