Can terminal ileitis cause diarrhea in patients with a history of inflammatory bowel disease, such as Crohn's disease?

Does Terminal Ileitis Cause Diarrhea?

Yes, terminal ileitis definitively causes diarrhea through multiple mechanisms including direct inflammatory damage to the ileal mucosa, bile acid malabsorption, and decreased absorptive surface area. 1

Mechanisms of Diarrhea in Terminal Ileitis

Direct Inflammatory Mechanisms

• Active inflammation of the terminal ileum produces diarrhea through mucosal damage, increased intestinal permeability, and impaired absorption of nutrients and fluids 1, 2
• Crohn's disease affecting the terminal ileum—the most common cause of terminal ileitis in Western populations—is explicitly listed as a cause of chronic diarrhea in established guidelines 1, 2
• The inflammatory process causes transmural involvement with wall thickening, ulcerations, and edema that directly impair normal absorptive function 1, 2

Bile Acid Malabsorption

• The terminal ileum is the exclusive site of bile acid reabsorption, making it particularly critical for preventing diarrhea 1
• When terminal ileal inflammation or resection occurs, bile acids are not reabsorbed and pass into the colon, where they stimulate secretion and cause characteristic postprandial diarrhea 1
• This bile acid diarrhea typically occurs after meals and usually responds to fasting and cholestyramine 1

Loss of Absorptive Surface

• Extensive inflammation or resection of the terminal ileum leads to diarrhea due to lack of absorptive surface, resulting in fat and carbohydrate malabsorption 1
• Decreased transit time through the inflamed segment further compounds malabsorption 1

Clinical Context in Inflammatory Bowel Disease

Crohn's Disease

• Approximately 50% of Crohn's disease patients have terminal ileal involvement, making diarrhea a cardinal presenting symptom 2
• The diarrhea may be accompanied by abdominal pain, weight loss, and systemic symptoms 3, 4
• Chronic diarrhea with terminal ileitis warrants full diagnostic evaluation including ileocolonoscopy with biopsies 1, 2

Ulcerative Colitis with Backwash Ileitis

• Up to 20% of patients with extensive ulcerative colitis develop "backwash ileitis"—continuous extension of inflammation from the cecum into the terminal ileum 2, 5
• These patients are prone to more refractory disease and increased risk of colon neoplasia 2
• The diarrhea in this context is typically more severe due to combined colonic and ileal involvement 5

Important Clinical Pitfalls

Do not assume all terminal ileitis causing diarrhea is Crohn's disease—infectious causes (Yersinia, Salmonella, Campylobacter, CMV) commonly present with acute diarrhea and terminal ileitis but are treatable and self-limited 2, 3, 6

In endemic regions, tuberculosis must be considered first as it is the primary cause of terminal ileal inflammation and presents with chronic diarrhea, strictures, and potential perforation 2

Nonspecific terminal ileitis has a generally benign course, with only 19.6% of patients eventually developing Crohn's disease, though persistent symptoms and endoscopic findings increase this risk significantly 7

Diagnostic Approach for Diarrhea with Terminal Ileitis

• Ileocolonoscopy with multiple biopsies from both lesions and normal-appearing mucosa is the gold standard 2, 5
• Stool cultures for bacterial pathogens and C. difficile toxin should always be performed, especially in acute presentations 2, 5
• Inflammatory markers (CRP, fecal calprotectin) help distinguish inflammatory from non-inflammatory causes 2
• Cross-sectional enterography (CT or MRI) assesses extent and severity, with severe inflammation showing wall thickening of 3-5mm, ulcerations, or high T2 intramural signal 1, 2, 5