Chronic diarrhoea
Define chronic diarrhoea?
Chronic diarrhoea may be defined as the abnormal passage of three or more loose or liquid stools per day for more than four weeks and/or a daily stool weight greater than 200 g/day.
IBS is one of the common causes of chronic diarrhoea although stool weight does not usually increase in IBS.
Discuss the causes of chronic diarrhoea?
Diarrhoea may result from: (a) colonic neoplasia/inflammation; (b) small bowel inflammation; (c) small bowel malabsorption; (d) maldigestion due to pancreatic insufficiency; or (e) motility disorders
Causes of chronic diarrhoea (Page v3)
Discuss the diagnostic approach to chronic diarrhoea?
Detailed history and examination
- to establish the likelihood that the symptoms are organic (as opposed to functional)
Symptoms suggestive of an organic disease include a history of diarrhoea of less than three months’ duration, predominantly nocturnal or continuous diarrhoea, significant weight loss and bleeding per rectum. The absence of these symptoms together with the positive symptoms as defined in ROME criteria is suggestive of IBS. - to distinguish malabsorptive from colonic/inflammatory forms of diarrhoea, and
Malabsorption causes passage of bulky malodorous pale stools (steatorrhoea). Colonic, inflammatory, or secretory forms of diarrhoea typically present with liquid loose stools with blood or mucous discharge. - to assess for specific causes of diarrhoea: Specific risk factors include
- Family history. Particularly of neoplastic, inflammatory bowel, or coeliac disease.
- Previous surgery- resections of the ileum and right colon lead to diarrhoea due to lack of absorptive surface and hence fat and carbohydrate malabsorption, decreased transit time, or bile acid malabsorption or Bacterial overgrowth (particularly in bypass operations). Chronic diarrhoea may also occur in up to 10% patients after cholecystectomy through mechanisms that include increased gut transit, bile acid malabsorption, and increased enterohepatic cycling of bile acids.
- Previous pancreatic disease
- Systemic disease. Thyrotoxicosis and parathyroid disease, diabetes mellitus, adrenal disease, or systemic sclerosis may predispose to diarrhoea through various mechanisms.
- Alcohol. Diarrhoea is common in alcohol abuse.
- Drugs: particularly magnesium containing products, antihypertensive and NSAIDS, theophyllines, antibiotics, antiarrhythmics, and antineoplastic agents) and food additives such as sorbitol and fructose
- Recent overseas travel or other potential sources of infectious gastrointestinal pathogens.
- Recent antibiotic therapy and Clostridium difficile infection.
- Lactase deficiency
Basic investigations
All patients with chronic diarrhoea should have FBC, LFTs, urea, electrolytes, TSH, Coeliac serology, CRP/ESR, Ca, albumin, B12, folate, Ferritin. High ESR, low albumin or anaemia have high specificity for organic disease. B12, folate, ferritin, calcium etc is part of a malabsorptive screen.
Chronic diarrhoea due to infectious agents is rare in immunocompetent patients but stool cultures should be considered, especially if there is a history of travel to high risk areas. Protozoan infections, such as giardiasis and amoebiasis, are most likely to result in chronic infections. Examination of three fresh stools for ova, cysts, and parasites remains the mainstay of diagnosis. If there is doubt about persisting Giardia infection, then stool ELISA for Giardia may be used. Similarly serology may be used for amoebiasis, where positive serology can differentiate invasive disease from the asymptomatic carrier state.
Further investigations are guided by the clinical suspicion of underling cause.
Colonic/inflammatory disease suspected: Most chronic diarrhoea is due to colonic disease, and in the absence of clinical evidence for malabsorption, investigations
should focus on the colon in the first instance. Colonic investigations should be age stratified, in keeping with the risk of neoplasia. Colonoscopy in patients >45 is indicated. Flexible sigmoidoscopy can be done in those <45 years of age.
Malabsorption suspected- Patients with malabsorption represent a small proportion of
presentations with chronic diarrhoea. Supporting history may direct investigations towards either the small bowel or pancreas.
Read the topic malabsorption- practical approach.
Difficult diarrhoea- If the above do not lead to a diagnosis, further tests may be needed
Stool weight- Ideally, stool weights over a 24–48 hour period should be recorded and may limit unnecessary investigation if values <200 g/day are obtained. This is often done on an inpatient basis.
Stool tests- Measurement of stool osmolality and gap is rarely of practical value in most cases of chronic diarrhoea and is non specific. Nevertheless, in difficult cases, particularly where factitious diarrhoea is suspected, these measurements may provide an aid to diagnosis.
Faecal fluid osmolality is similar to that of serum even in patients taking laxatives or those with osmotic or secretory diarrhoea. Low stool osmolality (<290 mosmol/kg) suggests contamination of stool with dilute urine, water, or excess ingestion of hypotonic fluid.
The faecal osmotic gap is calculated from the following formula: (290–2× (stool sodium +potassium concentration)). The osmotic gap of faecal fluid can be used to estimate the contribution of electrolytes and non-electrolytes to retention of water in the intestinal lumen. In secretory diarrhoea, unabsorbed electrolytes retain water in the lumen while in osmotic diarrhoea non- electrolytes cause water retention. Thus the osmotic gap should be large (>125 mosmol/kg) in osmotic diarrhoea and small (<50 mosmol/kg) in secretory diarrhoea. Further differentiation of osmotic and secretory diarrhoea may be provided by a trial of a 48 hour fast (usually as an inpatient). Continuation of diarrhoea despite this implies a secretory or factitious cause while cessation of diarrhoea during the fast is highly suggestive of osmotic diarrhoea. Dilutional, secretory, or osmotic diarrhoea may occur in factitious
diarrhoea. Osmotic diarrhoea may occur as a result of ingestion of magnesium salts.
Laxative screen- Repeated analysis of stool and urine is wise, as patients may
ingest laxatives intermittently.
Gut hormone profile- Hormone secreting tumours (VIPoma, gastrinoma, glucagonoma) arising from pancreatic tissue are rare causes of diarrhoea. Diarrhoea is often a prominent feature in carcinoid syndrome. This almost always occurs in the context of hepatic
metastases, even if the primary site remains undefined.
Despite extensive and exhaustive investigations, some cases will resist a definitive diagnosis. These will be those with watery, secretory, self limiting “idiopathic” diarrhoea (presumably infective), or undiagnosed factitious diarrhoea. Since in the majority of these cases the overall prognosis appears to be good, further investigation in this group is not warranted and symptomatic treatment should be instituted.
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