A pathologist reviewing biopsies from two patients with inflammatory bowel disease notes the following findings: Patient A has continuous inflammation extending from rectum to sigmoid colon, confined to mucosa and submucosa, with crypt abscesses and surface ulceration. Patient B has patchy inflammation in the terminal ileum and colon with transmural involvement and non-caseating granulomas. All of the following statements are correct EXCEPT:

Explanation

## Comparative Pathology: Ulcerative Colitis vs. Crohn Disease Patient A describes **ulcerative colitis** (continuous mucosal inflammation, crypt abscesses); Patient B describes **Crohn disease** (patchy, transmural, granulomas). The question asks which statement is INCORRECT. ### Pathologic and Clinical Comparison | Feature | Ulcerative Colitis (Patient A) | Crohn Disease (Patient B) | |---------|------|------| | **Distribution** | Continuous, rectum to colon | Patchy (skip lesions), any part of GI tract | | **Depth** | Mucosa + submucosa | Transmural | | **Granulomas** | Absent | Present (30–50%) | | **Complications** | Toxic megacolon, perforation | Fistulas, strictures, abscesses | | **Cancer risk** | High (7–10% at 20 years) | Moderate (2–4%) | | **Extraintestinal manifestations** | More common (30–40%) | Less common (15–20%) | ### Analysis of Each Statement **Statement 1 (Correct):** Patient A (UC) has mucosal inflammation that can lead to severe colitis and toxic megacolon. ✓ **Statement 2 (Correct):** Patient B (Crohn) has transmural inflammation → fistulas, strictures, and abscesses. Patient A (UC) has mucosal disease → these are rare in UC. ✓ **Statement 3 (Correct):** Both have increased cancer risk, but UC risk is higher (continuous inflammation) and Crohn risk is lower (patchy inflammation). ✓ **Statement 4 (INCORRECT):** Extraintestinal manifestations (arthritis, uveitis, erythema nodosum, primary sclerosing cholangitis) are **MORE common in ulcerative colitis** (30–40%) than in Crohn disease (15–20%). The statement reverses this relationship. **Key Point:** Ulcerative colitis, despite being a mucosal disease, has a higher incidence of extraintestinal manifestations than Crohn disease. This is a counterintuitive but well-established clinical fact. **High-Yield:** Do NOT confuse "mucosal disease = fewer systemic complications." UC has more extraintestinal manifestations because of its continuous, uniform inflammatory pattern and stronger immune dysregulation affecting the colon. **Mnemonic:** **EPIC** for UC extraintestinal manifestations: - **E**rythema nodosum - **P**rimary sclerosing cholangitis (PSC) — strongly associated with UC - **I**ritis/uveitis - **C**arthropathy (peripheral > axial) **Clinical Pearl:** Primary sclerosing cholangitis (PSC) is almost exclusively associated with ulcerative colitis, not Crohn disease. This is a key distinguishing feature. [cite:Robbins 10e Ch 17]