A 35-year-old man presents with intermittent loose stools containing blood and mucus for 12 months, weight loss and lower back pain. Abdominal examination is unremarkable. What is the most likely diagnosis?

Answer: B. Ulcerative colitis

Ulcerative colitis

Chronic (12-month) intermittent bloody, mucoid diarrhoea with weight loss and lower back pain in a young adult points to ulcerative colitis (UC).

Why UC fits

• Chronic bloody, mucoid diarrhoea is the hallmark colitic pattern of inflammatory bowel disease.
• Weight loss indicates organic disease (against a functional cause).
• Lower back pain suggests an IBD-associated spondyloarthropathy (sacroiliitis/ankylosing spondylitis) - an extraintestinal manifestation of UC.
• A normal abdominal examination does not exclude UC, especially distal/left-sided disease.

Confirming the diagnosis

• Sigmoidoscopy/colonoscopy and biopsy establish the extent, distinguish UC from Crohn's and monitor treatment.
• UC inflammation starts in the rectum and extends proximally in continuity, is superficial (mucosa/submucosa) and shows crypt abscesses with goblet-cell mucin depletion.