Chronic Diarrhea: Diagnosis and Management

Lawrence R. Schiller; Darrell S. Pardi; Joseph H. Sellin


Clin Gastroenterol Hepatol. 2017;15(2):182-193. 

In This Article

What Other Therapies Cause Chronic Diarrhea?


9. Radiation can cause chronic diarrhea, sometimes starting years after exposure. Clinicians should ask about a history of radiation therapy. (1a)

10. Patients with chronic diarrhea who have had abdominal surgery may require empiric therapy or diagnostic evaluation. (1a)

Radiation Enteritis. Radiation enteritis occurs in up to 20% of patients treated with pelvic irradiation, typically 1.5–6 years after irradiation, although later presentations are possible.[39] Risk factors include low body mass index, prior abdominal surgery, certain comorbidities, radiation dose, fractionation, and technique, as well as the concomitant chemotherapy.[39] Radiation enteritis is caused by direct damage to enterocytes and ischemia that is due to blood vessel damage. Submucosal fibrosis and lymphatic damage are commonly seen. The damaged bowel loses absorptive capacity and is predisposed to SIBO, particularly if strictures develop. If the distal ileum is involved, bile acid malabsorption (BAM) can be present. SIBO and BAM are discussed in more detail below.

Postsurgical Diarrhea. GI surgeries can lead to diarrhea that is due to intentional or inadvertent vagotomy, SIBO, BAM, and short bowel syndrome (SBS).

Vagotomy: Truncal vagotomy results in rapid gastric emptying of liquids and diarrhea.[40] The incidence of diarrhea is increased if vagotomy is accompanied by antrectomy and decreased after highly selective vagotomy without antrectomy.[40]

Bacterial Overgrowth: In health, the bacterial count in the proximal jejunum is <104/mL, and SIBO is typically defined as a bacterial count >105/mL.[41] Abdominal surgery predisposes to SIBO through disruption of the protective effect of stomach acid (eg, after vagotomy), stasis (eg, with an anastomotic stricture or partial bowel obstruction from adhesions), a blind limb (such as with an end-to-side anastomosis), or removal of the ileocecal valve. Bacterial overgrowth causes diarrhea by bile acid deconjugation, interfering with enzymatic action, and damage to the mucosa.[41] Bacterial overgrowth can be difficult to diagnose, because available tests are invasive and expensive (aspiration and culture of jejunal fluid) or have inadequate sensitivity and specificity (various breath tests).[42] Because of these concerns, some clinicians use response to a trial of antibiotics as a diagnostic test. However, the operating characteristics of this practice are unknown.

Bile Acid Malabsorption: The majority of intraluminal bile acids are reabsorbed in the distal ileum. If this area is damaged (eg, Crohn's disease, radiation enteritis) or resected, BAM can occur. Malabsorbed bile acids stimulate fluid secretion and motility in the colon, resulting in diarrhea. The diagnosis of BAM is difficult; it is usually made empirically and is supported by response to a bile acid binder.[43] In individuals with >100 cm ileal resection, bile acid binder therapy may paradoxically worsen diarrhea by exacerbating fat malabsorption caused by depletion of the bile acid pool.[43] BAM is implicated in post-cholecystectomy diarrhea, although the exact mechanisms are obscure.

Short Bowel Syndrome: SBS occurs after resection of a large proportion of the small intestine. SBS is not likely if >200 cm of small intestine remains,[44] although longer lengths will not protect against SBS if the remaining bowel is abnormal (eg, Crohn's disease or radiation enteritis). In SBS, the remaining absorptive surface is insufficient to preserve nutrient, fluid, and/or electrolyte homeostasis.[44] The risk of SBS also relates to which part of the small bowel is resected and whether it is in continuity with the colon.[44]