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