A 28-year-old man from Delhi presents with a 6-month history of bloody diarrhoea, abdominal pain, and weight loss of 8 kg. Colonoscopy reveals continuous mucosal inflammation and ulceration limited to the colon, with rectal involvement. Biopsy shows crypt distortion and crypt abscess formation but no granulomas. CT abdomen shows no fistulae or strictures. What is the most likely diagnosis?

Explanation

## Clinical Presentation and Distribution **Key Point:** The continuous mucosal inflammation limited to the colon with rectal involvement is pathognomonic for ulcerative colitis (UC). Crohn disease typically shows patchy (skip) lesions and can involve any part of the GI tract from mouth to anus. **High-Yield:** UC always involves the rectum and extends proximally in a continuous fashion; Crohn disease is segmental with normal mucosa between affected areas. ## Histopathological Findings | Feature | Ulcerative Colitis | Crohn Disease | |---------|-------------------|---------------| | Granulomas | Absent (90% of cases) | Present (30–50%) | | Crypt abscess | Common | Present but less prominent | | Depth of inflammation | Mucosa and submucosa only | Transmural (all layers) | | Skip lesions | Absent | Present | | Fissuring ulcers | Rare | Common | **Key Point:** The absence of granulomas on biopsy in this case supports UC over Crohn disease. Although granulomas are not present in all Crohn cases, their presence strongly favours Crohn disease. ## Distribution Pattern **Clinical Pearl:** The colonoscopic finding of continuous inflammation from rectum proximally, without skip lesions or fistulae, is diagnostic of UC. Crohn disease would show: - Skip lesions (patchy involvement) - Possible fistulae or strictures (transmural disease) - Potential small bowel involvement ## Why Other Diagnoses Are Excluded - **Infectious colitis:** Entamoeba histolytica causes flask-shaped ulcers with intact intervening mucosa; biopsy would show trophozoites or cysts, and serology would be positive. - **Ischaemic colitis:** Typically affects watershed areas (splenic flexure, rectosigmoid junction); acute presentation with bloody diarrhoea but resolves in days to weeks; no chronic inflammation pattern. **Mnemonic:** UC = **U**niform, **C**olon-only, **C**ontinuous. Crohn = **C**omplicated (fistulae, strictures), **C**ranial-to-anal (anywhere in GI tract), **C**reeping (transmural).