During a pathology teaching session, a faculty member displays histological slides from two patients with inflammatory bowel disease. Patient A shows mucosal and submucosal inflammation with crypt abscesses and surface ulceration, but the muscularis propria is spared. Patient B shows transmural inflammation with non-caseating granulomas and fissuring ulcers. What is the most common extraintestinal manifestation associated with Patient A's condition?

Explanation

## Most Common Extraintestinal Manifestation of Ulcerative Colitis **Key Point:** Primary sclerosing cholangitis (PSC) is the most common and most serious extraintestinal manifestation of ulcerative colitis, occurring in 1–4% of UC patients. It is strongly associated with UC and rarely occurs in Crohn disease. ### Extraintestinal Manifestations: Comparative Frequency | Manifestation | Ulcerative Colitis | Crohn Disease | Association Strength | | --- | --- | --- | --- | | **Primary sclerosing cholangitis (PSC)** | 1–4% (most common) | <0.5% | **UC-specific** | | **Erythema nodosum** | 2–4% | 2–4% | Equal in both | | **Pyoderma gangrenosum** | 1–2% | 1–2% | Equal in both | | **Ankylosing spondylitis** | 1–3% | 1–3% | Equal in both | | **Peripheral arthropathy** | 10–20% | 10–20% | Equal in both | ### Why PSC is UC-Specific **High-Yield:** Primary sclerosing cholangitis: 1. Occurs in 1–4% of UC patients but <0.5% of Crohn disease patients 2. Is characterized by progressive fibrosis and stricturing of intrahepatic and extrahepatic bile ducts 3. Leads to cholestasis, cirrhosis, and increased risk of cholangiocarcinoma 4. May persist or worsen even after colectomy (unlike other UC-related complications) 5. Is **independent of disease activity** — can occur with quiescent colitis ### Pathophysiology **Clinical Pearl:** The mechanism linking UC to PSC is incompletely understood but involves: - Molecular mimicry between bacterial antigens and bile duct epithelium - Altered gut permeability allowing bacterial translocation - Cross-reactive T-cell responses - Genetic predisposition (HLA-B8, DR3) ### Mnemonic for UC-Associated Complications **Mnemonic:** **SCARP** = Sclerosing cholangitis, Cirrhosis, Arthritis, Retinitis/Renal, Pyoderma - **S** = Sclerosing cholangitis (most UC-specific) - **C** = Cirrhosis (consequence of PSC) - **A** = Arthritis (peripheral and axial) - **R** = Retinitis, Renal amyloidosis - **P** = Pyoderma gangrenosum ### Why Other Options Are Wrong **Warning:** Erythema nodosum, pyoderma gangrenosum, and ankylosing spondylitis occur with **equal frequency** in both UC and Crohn disease. They are not specific to UC. PSC, however, is predominantly a UC complication.