Chronic Diarrhea

Today we talked about a patient with chronic diarrhea.

Here is a useful review article from Gastroenterology in 2004.

Guidelines from the American Gastroenterology Association were published in 1999.

Working up chronic diarrhea can be challening as the differential diagnosis is quite broad, clinical trials are lacking and expert opinion is varied.

Some key points:

1) Chronic diarrhea is not well defined. A reasonable definition might be:

• Decrease in stool consistency ("stool that takes the shape of the vessel it is in")
• >3 stools and/or >200g of stool per day
• >4 weeks duration

2) Have an organized approach to the types of chronic diarrhea (which leads to the differential). The guidelines suggest watery vs. inflammatory vs. fatty. Another classification scheme includes secretory vs. malabsorption/osmotic vs. inflammatory.

3) Use the history and physical exam to direct your initial set of investigations. Make sure to take a good medication and travel history!

4) Reasonable initial tests beyond the routine:

• Stool osmotic gap [290 - 2(stool Na + stool K)] and pH
• FOBT
• TSH
• anti-TTG and IgA level (if risk factors for celiac)
• Stool C&S, O&P (repeat over several days) and C.diff
• Fecal WBCs
• Response to fasting
• +/- 72 hour fecal fat testing (difficult to get done)
• +/- Colonoscopy or Sigmoidoscopy
• +/- Abdominal imaging

5) Stool osmotic gap (see above):

• a value less than 50 suggests secretory diarrhea (i.e. lots of secreted electrolytes in the lumen)
• a value greater than 125 suggests osmotic diarrhea (i.e. lots of unmeasured osmoles in lumen)
• values in between are indeterminate

6) Testing for pancreatic insufficiency, bacterial overgrowth, hormone levels (gastrin, calcitonin, VIP, carcinoid), mucosal abnormalities, etc. can be pursued as appropriate following the initial set of investigations.

7) Some authors suggest that more than 80% of chronic diarrhea cases have a treatable etiology.