A 28-year-old woman presents with a 6-month history of bloody diarrhea, abdominal cramping, and weight loss. Clinical examination reveals mild abdominal tenderness. Inflammatory markers (CRP and ESR) are elevated. Which investigation is most specific for confirming the diagnosis of ulcerative colitis?

Explanation

## Investigation of Choice for Ulcerative Colitis Diagnosis ### Why Colonoscopy with Mucosal Biopsies is Definitive **Key Point:** Colonoscopy with multiple mucosal biopsies is the gold standard and most specific investigation for confirming ulcerative colitis. It allows direct visualization of the colon and rectum, and histopathology differentiates UC from other colitides. ### Histopathologic Features on Biopsy | Feature | Ulcerative Colitis | Crohn's Disease | |---------|-------------------|------------------| | **Distribution** | Continuous, starts at rectum | Patchy, skip lesions | | **Depth** | Limited to mucosa & submucosa | Transmural | | **Crypt distortion** | Marked | Mild to moderate | | **Granulomas** | Absent | Present (50-60%) | | **Fissuring ulcers** | Rare | Common | **High-Yield:** The combination of continuous mucosal inflammation starting at the rectum + absence of granulomas on histology = ulcerative colitis. ### Endoscopic Findings in UC 1. **Mild disease:** Erythema, granularity, loss of vascular pattern 2. **Moderate disease:** Friability, spontaneous bleeding, mucus exudate 3. **Severe disease:** Ulceration, pseudopolyps, strictures **Clinical Pearl:** Multiple biopsies (at least 2 from rectum, 2 from sigmoid, 2 from descending colon) are essential because: - Confirms mucosal inflammation - Excludes infectious colitis (CMV, C. difficile) - Excludes malignancy - Assesses severity and dysplasia **Warning:** Endoscopy is contraindicated in fulminant colitis (risk of perforation) — clinical diagnosis + imaging suffice in that setting.