Terminal Ileitis and Diarrhea

Mechanisms of Diarrhea

The American Gastroenterological Association notes that active inflammation of the terminal ileum produces diarrhea through mucosal damage, increased intestinal permeability, and impaired absorption of nutrients and fluids 1, 3
The European Crohn’s and Colitis Organisation states that Crohn's disease affecting the terminal ileum is a common cause of chronic diarrhea in Western populations 1, 3
The inflammatory process causes transmural involvement with wall thickening, ulcerations, and edema that directly impair normal absorptive function, as reported by the Radiological Society of North America 4, 3
The terminal ileum is the exclusive site of bile acid reabsorption, making it critical for preventing diarrhea, according to the American Gastroenterological Association 1, 2
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, as noted by the American Gastroenterological Association 1, 2

Approximately 50% of Crohn's disease patients have terminal ileal involvement, making diarrhea a cardinal presenting symptom, as reported by the American Gastroenterological Association 3
Chronic diarrhea with terminal ileitis warrants full diagnostic evaluation including ileocolonoscopy with biopsies, according to the American Gastroenterological Association 5, 3
Up to 20% of patients with extensive ulcerative colitis develop "backwash ileitis", which is continuous extension of inflammation from the cecum into the terminal ileum, as noted by the American Gastroenterological Association 3, 6

Ileocolonoscopy with multiple biopsies from both lesions and normal-appearing mucosa is the gold standard for diagnosis, as reported by the American Gastroenterological Association 3, 6
Stool cultures for bacterial pathogens and C. difficile toxin should always be performed, especially in acute presentations, according to the American Gastroenterological Association 3, 6
Inflammatory markers (CRP, fecal calprotectin) help distinguish inflammatory from non-inflammatory causes, as noted by the American Gastroenterological Association 3
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, as reported by the Radiological Society of North America 4, 3, 6