Chronic diarrhoea in adults

Diarrhoea may be defined in terms of its duration, the volume of stool, its consistency, and the frequency of defaecation^{1 2} . A pragmatic definition of chronic diarrhoea is the persistent alteration from the norm with stool consistency between types 5 and 7 on the Bristol Stool Chart and increased frequency greater than four weeks in duration. Persistent diarrhoea suggests a non-infectious aetiology and therefore should be further investigated.

Epidemiology

In an American longitudinal community-based study, fewer than 2% of cases lasted longer than 14 days³ . However, another American population study, which took the cutoff point of four weeks, found a yearly population incidence of 5%⁴ .

Causes of chronic diarrhoea^{4 5}

• Irritable bowel syndrome (IBS).

• Bile acid malabsorption/diarrhoea⁶ .

• Colonic:
  

  • Diverticular disease.

  • Colonic neoplasia, including colorectal cancer.

  • Ulcerative colitis and Crohn's colitis.

  • Microscopic colitis: a type of inflammatory bowel disease, which typically presents in older age groups, with chronic watery diarrhoea. Colonoscopy appears normal and a definitive diagnosis can only be made with multiple colonic biopsies.

  • Ischaemic colitis.

  • Constipation with faecal impaction and overflow.

• Small bowel:
  

  • Coeliac disease.

  • Crohn's disease.

  • Other small bowel enteropathies - eg, Whipple's disease, tropical sprue, amyloid, intestinal lymphangiectasia.

  • Bile acid malabsorption - eg, Crohn's disease affecting the terminal ileum, after ileal resection, cholecystectomy, coeliac disease, bacterial overgrowth and pancreatic insufficiency.

  • Disaccharidase deficiency.

  • Lactose intolerance.

  • Small bowel bacterial overgrowth.

  • Mesenteric ischaemia.

  • Radiation enteritis.

  • Lymphoma.

• Pancreatic:
  

  • Chronic pancreatitis.

  • Pancreatic carcinoma.

  • Cystic fibrosis.

• Endocrine:
  

  • Hyperthyroidism.

  • Diabetes mellitus (and other causes of autonomic neuropathy).

  • Hypoparathyroidism.

  • Addison's disease.

  • Hormone-secreting tumours (VIPoma, gastrinoma, carcinoid).

• Chronic infection - eg, amoebiasis, giardiasis, hookworm, Cryptosporidium spp., Entamoeba histolytica (may be bloody diarrhoea).

• Recent antibiotic therapy and Clostridiodes difficile infection.

• Previous surgery:
  

  • Post-gastrectomy.

  • Extensive resections of the ileum and right colon lead to diarrhoea.

  • Bacterial overgrowth, particularly in bypass operations such as in gastric surgery and jejuno-ileal bypass procedures for morbid obesity.

  • Shorter resections of the terminal ileum can lead to bile acid diarrhoea that typically occurs after meals and usually responds to fasting and colestyramine

  • Chronic diarrhoea may also occur in up to 10% of patients after cholecystectomy^{[24534 : Suhr O, Danielsson A, Nyhlin H, et al remove]} .

• Drugs: for example, laxatives, antibiotics, digoxin, cytotoxic drugs, magnesium-containing antacids, metformin, non-steroidal anti-inflammatory drugs.

• Food additives such as sorbitol and fructose.

• Alcohol: diarrhoea is common in alcohol abuse.

• Immunodeficiency (including HIV).

• Factitious diarrhoea (may be associated with an eating disorder).

Presentation

• Symptoms suggestive of organic disease include a history of diarrhoea of less than three months in duration, predominantly nocturnal or continuous (as opposed to intermittent) diarrhoea and significant weight loss. The absence of these, in association with symptoms suggesting IBS and a normal physical examination suggest functional bowel disturbance but do not exclude organic gastrointestinal disease¹ .

• Malabsorption is often accompanied by steatorrhoea and the passage of bulky foul-smelling pale stools.

• Colonic, inflammatory or secretory forms of diarrhoea typically present with liquid loose stools with blood or mucous discharge.

Assessment^{4 5}

• Assess for the presence of any 'red flag' indicators suggesting a possible serious underlying cause:
  

  • Unintentional and unexplained weight loss.

  • Rectal bleeding.

  • Diarrhoea persisting for more than six weeks, in a person over 60 years of age.

  • Family history of bowel or ovarian cancer.

  • Abdominal mass.

  • Rectal mass.

  • Anaemia.

  • Raised inflammatory markers (may indicate inflammatory bowel disease).

• Look for other features suggesting an underlying cause (eg, recent travel abroad, laxative and other possible drug causes), features of systemic disease (eg, thyrotoxicosis, diabetes, adrenal insufficiency, systemic sclerosis), and features of pancreatic disease (eg, abdominal pain, steatorrhoea).

• Assess for features that indicate a diagnosis of IBS. Make a positive diagnosis following basic blood and stool screening tests¹ ..

• Always do a digital rectal examination in people with unexplained symptoms related to the lower gastrointestinal tract, provided this is acceptable to the person being examined.

Investigations⁵

• FBC: anaemia or raised platelet count suggesting inflammation.

• LFTs, including albumin level.

• U&Es.

• Tests for malabsorption: calcium, vitamin B12 and red blood cell folate, iron studies (ferritin).

• TFTs.

• ESR and CRP: elevated levels may indicate inflammatory bowel disease.

• Antibody tests for coeliac disease - IgA tissue transglutaminase antibody (tTGA), or IgA endomysial antibody (EMA).

• Ca125 if ovarian cancer is suspected.

• HIV serology if immunodeficiency is suspected.

• Stool for culture and sensitivity and examination for ova, cysts and parasites: if an infectious cause is suspected or there is a history of travel to high-risk areas. Consider sending stool for testing for C. difficile if a previous episode has resolved and the symptoms have recurred.

• Faecal calprotectin testing to help discriminate between IBS and inflammatory bowel disease in people under the age of 40 years if specialist assessment is being considered and cancer is not suspected.

• Testing for blood in the faeces in people with symptoms suggestive of colorectal cancer who do not meet suspected cancer referral pathway criteria.

Referral⁵

• Refer urgently under the two-week wait rules if red flag symptoms or signs are present:
  

  • They are aged 40 years and over with unexplained weight loss and abdominal pain; or

  • They are aged 50 years and over with unexplained rectal bleeding; or

  • They are aged 60 years and over with iron-deficiency anaemia or changes in their bowel habit, or tests show occult blood in their faeces.

• Consider a suspected cancer pathway referral (for an appointment within two weeks) for colorectal cancer in:
  

  • Adults with a rectal or abdominal mass.

  • Adults aged under 50 years with rectal bleeding and any of the following unexplained symptoms or findings:

    • Abdominal pain.

    • Change in bowel habit.

    • Weight loss.

    • Iron-deficiency anaemia.

Further investigations in secondary care⁴

• History or findings suggestive of malabsorption:
  

  • Small bowel:
    

    • Distal duodenal biopsies.

    • Barium follow-through.

    • Endoscopy.

    • Bacterial overgrowth: glucose hydrogen breath test, jejunal aspirate and culture.

  • Pancreatic:
    

    • CT scan of pancreas.

    • Faecal elastase or chymotrypsin.

    • Further structural tests: endoscopic retrograde cholangiopancreatography or magnetic resonance cholangiopancreatography.

  • History or findings suggestive of colonic or terminal ileal disease.

  • Flexible sigmoidoscopy in younger patients believed to have functional bowel disorder on clinical grounds (the diagnostic yield is not different to colonoscopy in this group).

  • Colonoscopy (barium enema is no longer indicated for the investigation of chronic diarrhoea).

  • Terminal ileum: barium follow-through. 99^m technetium-labelled white cell scanning is useful in testing for intestinal inflammation and has equivalent sensitivity to small bowel follow-through in the assessment of terminal ileal Crohn's disease.

  • Other more recent enhancements include video capsule endoscopy, enteroscopy, CT and MRI.

Further investigations

If the above tests are largely unremarkable and diarrhoea is persisting then the following should be considered:

• Inpatient assessment - may help to determine laxative abuse.

• 24- to 72-hour stool weights.

• Stool osmolality, osmotic gap.

• Laxative screen.

• Gut hormones: serum gastrin, vasoactive intestinal peptide (VIP), urinary 5-hydroxyindoleacetic acid (5-HIAA)⁷ .

Management

• This depends on the underlying cause.

• There may be a role for symptomatic treatment with antimotility drugs - eg, codeine, loperamide - in some cases but only when a definite diagnosis has been made and it is definite that there is no cause-associated contra-indication⁸ .