A 28-year-old man from Delhi presents with a 6-month history of bloody diarrhea, abdominal cramping, and weight loss of 4 kg. He reports 6–8 loose stools daily with blood and mucus. On examination, he is afebrile, with mild abdominal tenderness over the left lower quadrant. Laboratory investigations show hemoglobin 9.2 g/dL, ESR 48 mm/hr, and fecal calprotectin 320 μg/g (normal <50). Colonoscopy reveals continuous mucosal inflammation, friability, and ulceration extending from the rectum to the sigmoid colon, with normal mucosa proximally. Rectal biopsy shows 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 - **Continuous abdominal symptoms** over 6 months - **Weight loss** and anemia ### Key Diagnostic Features **Endoscopic Findings:** - **Continuous mucosal inflammation** from rectum to sigmoid (hallmark of UC) - Friability and ulceration confined to the colon - **Normal mucosa proximally** — UC does not skip areas **Histopathology:** - Crypt distortion and chronic inflammation in lamina propria - **Absence of granulomas** — rules out Crohn disease - Inflammation limited to mucosa and submucosa (not transmural) **Laboratory Markers:** - Elevated fecal calprotectin (320 μg/g) indicates active mucosal inflammation - Elevated ESR and anemia reflect chronic inflammation ### Differential Diagnosis Table | Feature | Ulcerative Colitis | Crohn Disease | Infectious Colitis | Ischemic Colitis | | --- | --- | --- | --- | --- | | **Distribution** | Continuous, rectum → proximal | Skip lesions | Variable | Watershed areas | | **Depth** | Mucosa/submucosa | Transmural | Mucosal | Mucosal/submucosal | | **Granulomas** | Absent | Present (50%) | Absent | Absent | | **Rectal involvement** | Always | Variable | Variable | Spared | | **Duration** | Chronic (>4 weeks) | Chronic/relapsing | Acute (days) | Acute/subacute | **Key Point:** The **continuous distribution from rectum without skip lesions** and **absence of granulomas** are pathognomonic for ulcerative colitis. **High-Yield:** UC is confined to the **colon and rectum only**; small bowel involvement is diagnostic of Crohn disease. **Clinical Pearl:** Fecal calprotectin >250 μg/g indicates active IBD; values >400 suggest moderate-to-severe disease. [cite:Robbins 10e Ch 17]