Bile Acid Diarrhoea

Bile acid diarrhoea is chronic watery diarrhoea caused by excess bile acids reaching the colon. It is common and under diagnosed, and it accounts for about 25% to 33% of patients labelled with diarrhoea predominant irritable bowel syndrome.

Type 1 follows ileal disease or resection (Crohn disease, over 100 cm of ileum resected), type 2 is idiopathic (bile acid overproduction, low FGF19) and type 3 follows other gastrointestinal disease or surgery (cholecystectomy, pancreatitis, coeliac disease, small bowel bacterial overgrowth, radiation).

Pathophysiology.

Failure of ileal reabsorption of bile acids, or hepatic overproduction because of reduced FGF19 feedback, raises colonic bile acid concentrations. These stimulate colonic secretion, motility and mucosal injury, producing watery diarrhoea and urgency.

Chronic watery diarrhoea, urgency, faecal incontinence (especially at night and after meals), bloating, abdominal discomfort and often a history of ileal disease or cholecystectomy. Weight loss is uncommon unless there is steatorrhoea.

Red flags.

• Weight loss or anaemia.
• Nocturnal diarrhoea with blood.
• Age over 50 years with new diarrhoea.
• Family history of bowel cancer.

Exclude other causes: faecal calprotectin, coeliac serology, thyroid tests, stool culture and, when needed, colonoscopy with biopsies for microscopic colitis. Selenium-75 homotaurocholic acid retention test (7-day retention under 10% is abnormal, under 5% is severe) is the reference test, where available. Serum 7-alpha-hydroxy-4-cholesten-3-one over 52.5 ng/mL (fasting) and faecal bile acids are alternatives. A response to a bile acid sequestrant supports the diagnosis.

Differential diagnosis.

• Irritable bowel syndrome with diarrhoea.
• Microscopic colitis.
• Coeliac disease.
• Small bowel bacterial overgrowth.
• Pancreatic exocrine insufficiency.
• Crohn disease.

Bile acid sequestrants are the first treatment. Treat underlying disease, and replace fat soluble vitamins in prolonged steatorrhoea.

• Colestyramine: 4 g orally once daily, increased every 3 to 7 days to a usual dose of 4 g two to four times daily, taken with meals; long term; maximum 16 g daily; monitor bowel function, constipation and fat soluble vitamins; take other drugs 1 hour before or 4 to 6 hours after; avoid in complete biliary obstruction.
• Colesevelam (alternative if colestyramine is poorly tolerated): 625 mg orally, increased from 1 tablet twice daily to 3 tablets twice daily (1,875 mg twice daily); maximum 3,750 mg daily; monitor triglycerides and vitamins; avoid with bowel obstruction and triglycerides over 5.6 mmol/L.
• Loperamide (adjunct): 2 mg orally after each loose stool; maximum 16 mg daily; monitor for constipation and ileus; reduce in hepatic impairment.

Dietary fat reduction helps some patients. If sequestrants fail, FXR agonists are specialist options.

Monitoring. Stool frequency at 4 weeks and 3 months; vitamin D, A, E, K and B12 yearly in long term treatment.

Referral and escalation. Gastroenterology when the diagnosis is unclear or treatment fails.