Understanding Diarrhoea Types and Causes

Study Notes

Diarrhoea

Diarrhoea is characterized by 3 or more loose stools per day or more frequent stool passage than normal for the individual.
Acute diarrhoea lasts 14 days or less and is usually caused by an infectious agent.
Persistent diarrhoea lasts 15-30 days.
Chronic diarrhoea lasts longer than 30 days.

Types of Diarrhoea

Secretory Diarrhoea: Watery diarrhoea that occurs independently of ingested substances.
- Active secretion of water, potassium, and bicarbonate into the intestinal lumen through the inhibition or activation of enzymes.
- Causes:
  - Neuroendocrine disorders (e.g., carcinoid syndrome, gastrinoma)
  - Endocrine disorders (e.g., hyperthyroidism, Addison disease, diabetes)
  - Foodborne infections (e.g., cholera, enterotoxigenic E. coli, viruses)
Osmotic Diarrhoea: Watery diarrhoea related to ingestion of food or medication.
- Poor absorption or excessive ingestion of hydrophilic substances (e.g., salts, sugars, laxatives) draws water into the intestinal lumen.
- Causes:
  - Osmotic laxatives (e.g., magnesium citrate)
  - Carbohydrate malabsorption (e.g., lactose intolerance)
Inflammatory Diarrhoea: Occurs due to damage to the intestinal mucosa.
- Damage to the intestinal mucosa can result in:
  - Cytokine-induced water hypersecretion
  - Impaired absorption of osmotically active substances
  - Fat and/or disruption of water and electrolyte absorption
  - Mucus, blood, and leukocytes are present in the stool.
- Causes:
  - Inflammatory bowel disease (IBD): ulcerative colitis (UC), Crohn’s disease
  - Colorectal cancer
  - Infections:
    - Shigellosis (bacillary dysentery)
    - Nontyphoidal salmonellosis (salmonella gastroenteritis)
Altered Motility Diarrhoea: Increased bowel activity causes rapid intestinal passage, reducing the time for water and electrolytes to be absorbed.
- Causes:
  - Diarrhoea-predominant IBS (IBS-D)
  - Prokinetics (drugs that stimulate contractions along the GIT)

Irritable Bowel Syndrome (IBS)

Characterized by altered bowel habits (diarrhoea, constipation or mixed) associated with abdominal pain that is influenced by defecation.
Pathophysiology:
- Altered GI motility (increased frequency and/or irregularity of bowel contractions)
- Visceral hypersensitivity/hyperalgesia
- Altered permeability of GI mucosa
- Psychosocial aspects
Clinical features:
- Abdominal pain often related to defecation and alleviated by it.
- Altered bowel habits (diarrhoea, constipation, or alternating).
- Other symptoms such as nausea, reflux, early satiety, mucus passing, bloating, pain, fatigue, disturbed sexual function, increased urinary frequency and urgency, and in females, dysmenorrhea.
- Physical exam is usually normal.

Inflammatory Bowel Disease (IBD)

Crohn’s Disease (CD)*
Can affect any part of the GIT (from mouth to colon).
Characterized by “skip lesions,” discrete areas of inflamed tissue interspersed with healthy tissue.
Transmural inflammation, meaning it penetrates the entire thickness of the bowel wall.
Can lead to thickening of the bowel wall (mural thickening) and fibrosis.
Can cause fistulas, strictures, and abscesses.