Diarrhoea and rectal bleeding.
Diarrhoea is the passage of >300ml of liquid feaces/24hrs.
In determining the cause there are three major questions to ask:
1. Is the diarrhoea acute or chronic? Infections are often acute (has the patient been abroad?). Chronic diarrhoea alternating with constipation suggests irritable bowel syndrome. Medication abuse eg. Antacids.
2. Is the large or small bowel to blame? In the former stools are watery with mucus or blood and there is lower abdominal pain with tenesmus and urgency; in the later any pain is often periumbilical or in the RIF and the stools are bulky and stink.
3. Is there a non-GI cause? Eg thyrotoxicosis, anxiety, or autonomic neuropathy from DM (nocturnal diarrhoea) drugs like antacids, cimetidine, digoxin, antibiotics, thiazide diuretics and alcohol.
Osmotic causes of diarrhoea: laxatives: lactulose, magnesium sulphate.
Secretory causes: infections: bacteria: Campylobacter, V.cholerae, Staphylococcus, E coli, Salmonella, Shigella, Clostridium difficile; giardiasis; rotavirus; amoebiasis.
Inflammatory bowel disease: UC, Crohn's disease.
Laxative abuse; bile salts, malabsorption.
Increased motility: irritable bowel syndrome; thyrotoxicosis.
Refer: Diarrhoea.
Causes of bloody diarrhoea: dysentery: Campylobacter, Salmonella, Shigella and E coli infections; amoebiasis; UC; Crohn's disease; colorectal cancer; pseudomembranous and ischaemic colitis.
Causes of rectal bleeding (± diarrhoea): diverticulitis; colonic cancer; polyps; haemorrhoids; radiation proctitis; trauma; fissure-in-ano; angiodysplasia, a common cause of bleeding in the elderly due to arteriovenous malformation.
Investigations: PR to exclude overflow diarrhoea. Large bowel diarrhoea: fresh stool for pathogens, ova and cysts. Sigmoidoscopy, barium enema ± colonoscopy if prolonged.
If a small bowel cause is suspected: rule out malabsorption; do faecal fats analysis and measure serum folate and iron. Consider a small bowel barium meal and biopsy.
Management: treat the cause, Fluids PO. Check U and E, if IV fluid is needed, give 0.9% saline with ³ 20mmol K/l. If it is necessary to reduce symptoms try codeine phosphate.
Refer: Rectal bleed.