Distinguishing features between ulcerative colitis and crowns disease from harrison
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Now I have all the information I need from Harrison's. Let me compile the comprehensive answer on distinguishing features between UC and Crohn's disease.
Distinguishing Features: Ulcerative Colitis vs. Crohn's Disease
From Harrison's Principles of Internal Medicine, 22nd Edition (2025)
1. Location and Distribution
| Feature | Ulcerative Colitis (UC) | Crohn's Disease (CD) |
|---|---|---|
| Site of involvement | Colon only | Any part of GI tract (mouth to anus) |
| Distribution | Continuous, confluent from rectum proximally | Segmental ("skip lesions") |
| Rectal involvement | Almost always (rectal sparing is atypical) | Rectum often spared |
| Small bowel | Never (except backwash ileitis in pancolitis) | Commonly involved (especially terminal ileum) |
| Perianal disease | Rare (occasional fissures/hemorrhoids) | Common - fistulae, abscesses, tags |
2. Macroscopic / Endoscopic Features
| Feature | UC | CD |
|---|---|---|
| Ulcers | Superficial, continuous mucosal ulceration | Deep, serpiginous, or linear ("cobblestone" appearance) |
| Bowel wall | Thin, mucosa-limited | Thickened ("hose-pipe" appearance), transmural |
| Strictures | Rare (~5%); suggest malignancy | Common (fibrostenotic type) |
| Fistulae | Absent | Hallmark feature - enteroenteric, enterovesical, enterocutaneous |
| "Skip lesions" | Absent | Present |
| Pseudopolyps | Present (islands of regenerating mucosa) | Less common |
- In UC, severe disease shows spontaneous bleeding and frank ulcerations. In colonoscopy, UC shows "erythema, friability, and exudates" (Fig. 337-7).
- In CD, cobblestoning results from deep ulcers separated by areas of relatively normal intervening mucosa.
3. Histological Features
| Feature | UC | CD |
|---|---|---|
| Depth of inflammation | Mucosal and submucosal only | Transmural (full thickness) |
| Granulomas | Absent | Present in ~30-50% (non-caseating) - pathognomonic |
| Crypt abscesses | Present and prominent | May be present |
| Goblet cell depletion | Prominent | Less prominent |
| Fibrosis | Less common | Common (transmural fibrosis) |
| Lymphoid aggregates | Rare | Common (transmural lymphoid aggregates) |
Harrison's notes: "The presence of multiple, separate, sharply delineated areas of disease resulting in skip lesions is characteristic [of CD], and when present, differentiates Crohn's disease from UC."
4. Clinical Features
| Feature | UC | CD |
|---|---|---|
| Bleeding per rectum | Hallmark - almost universal | Variable; less common in small bowel CD |
| Diarrhea | Bloody, frequent, small volume | May be non-bloody; large volume watery |
| Abdominal pain | Less prominent; cramping before defecation | Prominent, often RLQ colicky pain (mimics appendicitis) |
| Tenesmus | Common (rectal involvement) | Less common |
| Palpable mass | Rare | Common (RLQ mass in ileocolitis) |
| Weight loss/malnutrition | Mild | More severe, due to malabsorption |
| Fever | In severe attacks | More common; high-spiking suggests abscess |
| Toxic megacolon | Occurs (transverse colon >6 cm) | Rare |
| Anal fissures/fistulae | Occasional fissures only | Extensive perianal disease typical |
5. Disease Patterns
CD evolves toward one of two patterns (Harrison's Table 337-5):
- Fibrostenotic / obstructing pattern - leads to strictures, obstruction
- Penetrating / fistulous pattern - leads to abscesses, fistulae
UC has no such penetrating behavior; it progresses in mucosal inflammation severity.
6. Complications
| Complication | UC | CD |
|---|---|---|
| Colorectal cancer | Significantly increased risk (pancolitis, long duration) | Moderately increased; also small bowel cancer risk |
| Fistulae | No | Yes - gastrocolic, enterovesical, enterocutaneous, perianal |
| Abscesses | Rare | Common (intraabdominal, perianal) |
| Strictures/obstruction | Rare (~5%) | Common, due to fibrosis |
| Toxic megacolon | Yes | Rare |
| Perforation | Can occur (mortality ~15% with toxic megacolon) | Less common |
| Nephrolithiasis | Oxalate stones (after colectomy) | Oxalate stones (fat malabsorption) |
| Gallstones | Less common | More common (ileal disease - bile salt malabsorption) |
| Malabsorption | Not significant (colon-limited) | Yes - especially with small bowel disease |
7. Extraintestinal Manifestations
Both share extraintestinal manifestations, but some differences exist:
| Manifestation | UC | CD |
|---|---|---|
| Primary sclerosing cholangitis (PSC) | More common (strongly associated) | Less common |
| Uveitis/episcleritis | Present | Present |
| Erythema nodosum | Yes | Yes |
| Pyoderma gangrenosum | Yes | Yes |
| Peripheral arthritis | Correlates with bowel activity | Correlates with bowel activity |
| Ankylosing spondylitis / axial SpA | Yes | Yes (slightly more common) |
| Perianal skin tags | Rare | Common |
| Oral aphthous ulcers | Occasional | More common |
8. Laboratory / Serological Markers
| Marker | UC | CD |
|---|---|---|
| pANCA (perinuclear antineutrophil cytoplasmic Ab) | Positive in ~60-70% | Negative / low |
| ASCA (anti-Saccharomyces cerevisiae Ab) | Negative | Positive in ~60-70% |
| Anti-OmpC, anti-CBir1, anti-A4-Fla2 | Negative | More often positive |
| CRP / ESR | Elevated in active disease | Often more elevated |
| Fecal calprotectin | Elevated | Elevated |
The pANCA+/ASCA- pattern favors UC; pANCA-/ASCA+ pattern favors CD (Harrison's).
9. Imaging
| Feature | UC | CD |
|---|---|---|
| Small bowel imaging | Normal | Thickened loops, "string sign" (Kantor), stenoses |
| CT/MRI enterography | Mural thickening limited to colon | Transmural thickening, mesenteric "fat creeping," fistulae |
| Barium enema | "Lead-pipe" colon (loss of haustration), pseudopolyps | Cobblestoning, skip lesions, fistulae |
10. Response to Surgery
| UC | CD | |
|---|---|---|
| Colectomy = cure? | YES - total proctocolectomy is curative | NO - disease recurs in remaining bowel |
| Surgical indication | Toxic megacolon, dysplasia, refractory disease | Obstruction, fistulae, abscesses, refractory disease |
| Recurrence after surgery | N/A (cured) | High recurrence rate at anastomotic sites |
Key Mnemonic Summary
UC - Continuous, Colon only, Crypt abscesses, Curable by colectomy, pANCA positive, Carcinoma risk high.
CD - Discontinuous (skip), Deep (transmural), Diarrhea/fistulae, Distal ileum common, Drainable abscesses, non-Destructible (surgery not curative), ASCA positive.
Harrison's Principles of Internal Medicine, 22nd Edition (2025), Chapter 337 - Inflammatory Bowel Disease, pp. 2594-2654.
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