Diarrhoea Revision PBL

Definition Diarrhoea is defined as: – >3 bowel motions per day – Looser than normal stools – Stool volume > 300g – May be associated with ugency

Types of diarrhoea Secretory (non-invasive) – Decreased intestinal absorption and increased intestinal secretion into the lumen resulting in watery diarrhoea – Commonly caused by: Enterotoxins: eg cholera, E coli Hormones: vasoactive intestinal peptide Bile salts and fatty acids in the colon (following ileal resection) Some laxatives (eg docusate sodium) – In watery diarrhoea, loss of fluids and salts often results in dehydration

Types of diarrhoea Invasive/Inflammatory – Caused by organisms invading the mucosa or inflammation primarily affecting the large bowel – This usually results in bloddy diarrhoea – There is also defective absorption of fluids & electrolytes – Common causes: Infective conditions: dystenery due to Shigella and E Histiolytica Inflammatory: UC and Crohn’s disease

Types of diarrhoea Osmotic – Caused by generalised malabsorption so that high concentrations of solute remain in the lumen Specific defect in absorption (eg disaccharide deficiency or glucose-galactose malabsorption) Ingested non-absorbed hypertonic substance (eg a purgative such as magnesium sulphate or Mg- containing antacid. – The volume of diarrhoea in this type is decreased by the absorption of fluid by the ileum & colon

Types of diarrhoea Abnormal motility – Generally of upper GIT so that frequency of defecation is high although volume is not (not true diarrhoea) – Caused by: Diabetes Removal of vagus nerve Hyperthyroidism

Common infections Rotavirus – Self-limiting infection with watery diarrhoea Shigella – Gram-negative bacteria causing abdominal cramping, high-grade fever and large volume watery diarrhoea lasting 3-7 days Salmonella – Gram-negative anaerobes causing abdo cramping and self-limiting watery diarrhoea Giardia – Protozoan parasite, water-borne causing acute and chronic watery diarrhoea, malabsorption, weight loss and abdo cramping Other causes – staphylococcus, campylobacter jejuni, clostridium, Escherichia coli, adenoviruses, etc.

Drug treatment Rehydration is the most important therapy for diarrhoea! Antibiotics for infective diarrhoea Anti-diarrhoeal agents – Decreases gut motility – Muscarinic receptor antagonists – reduce spasms (e.g. Atropine) – Opiates (reduce motility) – main ones are codeine, diphenoxylate, loperamide – Loperamide – selective for GI tract, does not cross BBB, less SE