Is left-sided abdominal pain more commonly associated with Crohn's (Crohn's disease) or ulcerative colitis in patients with inflammatory bowel disease (IBD)?

Left-Sided Abdominal Pain: More Common in Ulcerative Colitis

Left-sided abdominal pain is more characteristic of ulcerative colitis than Crohn's disease, because UC typically involves the left colon (rectum extending proximally in a continuous pattern), whereas Crohn's disease most commonly affects the terminal ileum and right colon. 1, 2

Anatomical Distribution Patterns

Ulcerative Colitis:

• Begins in the rectum and extends proximally in a continuous fashion, commonly affecting the left colon (rectosigmoid, descending colon) 3, 1, 4
• Left-sided colitis is a recognized subtype of UC, specifically involving the rectum through the descending colon 5
• The continuous inflammation pattern means left-sided disease produces left lower quadrant pain 4
• In left-sided UC, 58.8% of patients have rectosigmoid involvement only 6

Crohn's Disease:

• The terminal ileum is the most commonly affected site, typically producing right lower quadrant pain 1, 2
• Shows patchy, discontinuous distribution with skip lesions throughout the GI tract 1, 2
• Can affect any part of the GI tract from mouth to anus, but isolated left colon involvement is uncommon 1
• Rectal sparing occurs commonly in CD, whereas the rectum is almost always involved in UC 1, 7

Clinical Presentation Differences

Pain Location by Disease:

• UC patients with left-sided colitis present with left lower quadrant pain or tenderness that is often relieved by defecation 4
• CD patients more commonly present with right lower quadrant pain when the terminal ileum is involved 2
• The classic UC presentation includes bloody diarrhea with mucus, rectal urgency, tenesmus, and variable abdominal pain 4

Important Diagnostic Caveats

When Left-Sided Pain Suggests Crohn's:

• If left-sided pain occurs with rectal sparing on colonoscopy, strongly consider CD rather than UC 1, 7
• Segmental left-sided colitis in the setting of diverticulosis may represent segmental colitis associated with diverticulosis, CD, or IBD-unclassified 3
• Patchy cecal inflammation ("cecal patch") can occur in 75% of left-sided UC cases, but this represents skip inflammation in the right colon, not left-sided disease 3, 6, 8

Diagnostic Workup Required:

• Perform complete ileocolonoscopy with at least two biopsies from five different sites (terminal ileum, ascending, transverse, descending, sigmoid, rectum) to differentiate UC from CD 1, 7
• Cross-sectional imaging (CT or MRI enterography) is essential because approximately one-third of CD patients have small bowel disease not detectable by colonoscopy 1, 7
• In elderly patients presenting with left-sided abdominal pain and colitis, consider alternative diagnoses including ischemic colitis, diverticular disease, segmental colitis associated with diverticulosis, and colorectal cancer 3

Key Distinguishing Features

Histological Confirmation:

• UC shows continuous mucosal inflammation limited to mucosa/submucosa 1, 9
• CD demonstrates transmural inflammation with potential granulomas and focal, patchy distribution 1, 2
• Crypt abscesses are more common in UC (41%) than CD (19%) 7

Clinical Implications:

• In 5-15% of IBD cases, endoscopic and histological evaluation cannot distinguish between CD and UC; capsule endoscopy can establish definitive CD diagnosis by demonstrating small intestine lesions in 17-70% of these patients 1, 7
• Patients with left-sided UC and a cecal patch are younger (median age 31 vs 41 years) and more likely to eventually be diagnosed with CD (9.8% vs 1.0%) during follow-up 6