Terminal Ileitis Etiologies and Diagnostic Approaches

Primary Etiologies

• The American Gastroenterological Association notes that Crohn's disease is the most frequent cause of terminal ileal ulcers in Western populations, characterized by transmural inflammation that commonly affects the terminal ileum 2
• Endoscopic features of Crohn's disease include aphthous ulcers, longitudinal ulcers, cobblestone appearance, and skip lesions 1
• Histopathology of Crohn's disease shows focal chronic inflammation, transmural involvement, small non-caseating granulomas, and crypt architectural distortion 1, 2
• Approximately 50% of patients with Crohn's disease require surgery within 10 years of diagnosis due to complications 1
• Infectious causes, such as Yersinia enterocolitica, Salmonella, Shigella, and Campylobacter species, can cause acute terminal ileitis that typically resolves with appropriate antimicrobial therapy 1, 2
• Cytomegalovirus can cause terminal ileal ulcers, particularly in immunocompromised patients 2
• The European Crohn’s and Colitis Organisation recommends stool cultures should be performed, especially in acute presentations 1
• In India and other endemic regions, intestinal tuberculosis is the primary etiology of terminal ileal ulcers, followed by Crohn's disease 1
• Tuberculosis typically affects the ileocecal region with circumferential ulcers, strictures, and occasionally perforation 1
• Histopathology of tuberculosis shows large granulomas (often multiple and confluent) with caseous necrosis and acid-fast bacilli 1
• Untreated tuberculosis leads to strictures, perforation, and fistula formation 1
• The American College of Gastroenterology notes that continuous extension of inflammation from the cecum into terminal ileum occurs in up to 20% of patients with extensive ulcerative colitis 3, 2
• Patients with backwash ileitis are prone to more refractory disease with increased risk of colon neoplasia 3
• Additional small bowel imaging should be considered to differentiate from Crohn's disease 3
• Microscopic colitis (collagenous or lymphocytic) can occasionally involve the terminal ileum with increased intraepithelial lymphocytes 2

Diagnostic Algorithm

• Ileocolonoscopy with multiple biopsies from both visible lesions and normal-appearing mucosa is the gold standard for diagnosis 1, 2
• Stool cultures for bacterial pathogens and C. difficile toxin should be performed 3, 1
• Inflammatory markers (CRP, fecal calprotectin) should be measured 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 2

Critical Pitfalls

• Do not assume all terminal ileitis is Crohn's disease—infectious causes are common and treatable, particularly in acute presentations 1
• In endemic regions, always consider tuberculosis first and obtain appropriate testing including acid-fast bacilli staining 1
• Do not perform appendectomy in the presence of terminal ileitis—this significantly increases risk of intra-abdominal septic complications and fistulas 5