A 28-year-old woman from Delhi presents with a 6-month history of bloody diarrhoea (8–10 stools/day), left lower abdominal cramping pain, and weight loss of 4 kg. On examination, she is afebrile with mild left lower abdominal tenderness. Laboratory investigations show Hb 9.2 g/dL, ESR 68 mm/hr, CRP 12 mg/dL. Colonoscopy reveals continuous mucosal inflammation with friability and ulceration limited to the rectum and sigmoid colon. Histopathology shows crypt distortion, crypt abscess formation, and acute inflammatory infiltrate confined to the mucosa and submucosa. Which of the following is the most likely diagnosis?

Explanation

## Diagnosis: Ulcerative Colitis ### Clinical Presentation **Key Point:** The clinical triad of bloody diarrhoea, left lower abdominal pain, and weight loss in a young woman is classic for inflammatory bowel disease. **High-Yield:** Ulcerative colitis typically presents with: - Continuous mucosal inflammation (not patchy) - Rectal bleeding (blood mixed with stool) - Tenesmus and urgency - Systemic features: anaemia, elevated inflammatory markers ### Endoscopic Findings **Clinical Pearl:** The **continuous distribution** of inflammation starting from the rectum and extending proximally (without skip lesions) is pathognomonic for ulcerative colitis. | Feature | Ulcerative Colitis | Crohn's Disease | |---------|-------------------|------------------| | **Distribution** | Continuous, rectum → proximal | Patchy, skip lesions | | **Depth** | Mucosa + submucosa only | Transmural (all layers) | | **Crypt changes** | Crypt distortion, crypt abscess | Granulomas (60%), fissuring ulcers | | **Complications** | Toxic megacolon, perforation | Fistulas, strictures, perianal disease | ### Histopathology **Key Point:** The **mucosal and submucosal involvement only** (no transmural disease) with crypt abscess formation and acute inflammatory infiltrate is diagnostic of ulcerative colitis. **Mnemonic: MUCOSA** — Mucosal disease, Ulceration, Continuous involvement, Oedema, Submucosal inflammation, Acute cryptitis ### Laboratory Findings **High-Yield:** Elevated ESR and CRP reflect active inflammation; anaemia is due to chronic blood loss and iron deficiency. ### Why This Is Ulcerative Colitis, Not Crohn's - **No skip lesions** → rules out Crohn's - **No transmural involvement** → rules out Crohn's - **No granulomas** → rules out Crohn's - **Continuous rectal involvement** → typical of UC [cite:Robbins 10e Ch 17]