A 28-year-old woman from Mumbai presents with a 6-month history of bloody diarrhea, abdominal cramping, and weight loss of 4 kg. She reports 6–8 loose stools daily with visible blood and mucus. On examination, she is afebrile, with mild left lower quadrant tenderness. Laboratory investigations show hemoglobin 9.2 g/dL, ESR 62 mm/h, CRP 8.5 mg/dL, and fecal calprotectin 450 µg/g. Colonoscopy reveals continuous mucosal inflammation, friability, and ulceration limited to the rectum and sigmoid colon, with normal mucosa proximally. Multiple biopsies show crypt distortion, increased chronic inflammation in the lamina propria, and absence of granulomas. What is the most likely diagnosis?

Explanation

## Diagnosis: Ulcerative Colitis ### Clinical Presentation The patient presents with the classic triad of ulcerative colitis (UC): - Bloody diarrhea with mucus - Abdominal cramping - Weight loss and systemic inflammation (elevated ESR, CRP) ### Key Distinguishing Features | Feature | Ulcerative Colitis | Crohn's Disease | |---------|-------------------|------------------| | **Distribution** | Continuous, starts rectally | Skip lesions, patchy | | **Depth** | Mucosa and submucosa only | Transmural | | **Granulomas** | Absent | Present in 30–50% | | **Crypt distortion** | Present | Present | | **Fistulas/strictures** | Rare | Common | **Key Point:** The **continuous mucosal inflammation limited to rectum and sigmoid colon** is pathognomonic for UC. Crohn's disease typically shows skip lesions (patchy distribution with normal intervening mucosa). **High-Yield:** Absence of granulomas on biopsy strongly favors UC over Crohn's disease. Granulomas are found in only 30–50% of Crohn's cases but are virtually absent in UC. ### Pathologic Findings in UC 1. **Mucosal and submucosal inflammation** — neutrophilic infiltration 2. **Crypt distortion** — loss of normal architecture 3. **Crypt abscess** — neutrophils within crypt lumens 4. **Absence of transmural involvement** — distinguishes from Crohn's 5. **No granulomas** — key negative finding **Clinical Pearl:** Fecal calprotectin >250 µg/g indicates active IBD; this patient's level of 450 µg/g confirms significant mucosal inflammation. ### Why UC and Not Crohn's? - Continuous distribution (not skip lesions) - Limited to colon (not small bowel involvement) - Mucosal-only disease (not transmural) - No granulomas on histology - Rectal involvement (UC typically starts here and spreads proximally)