What is ulcerative colitis?

What is Ulcerative Colitis

Ulcerative colitis is a chronic inflammatory bowel disease characterized by continuous mucosal inflammation that begins in the rectum and extends proximally through the colon in a confluent pattern, presenting classically with bloody diarrhea. 1

Disease Definition and Pathophysiology

Ulcerative colitis is a chronic idiopathic inflammatory disorder limited to the colonic mucosa, resulting from dysregulated immune responses to intraluminal antigens in genetically susceptible individuals. 1, 2 The inflammation is superficial, affecting only the mucosal layer (unlike Crohn's disease which is transmural), and characteristically starts at the anal verge and extends proximally in a continuous, confluent fashion with clear demarcation between inflamed and normal areas. 1

The etiology remains unknown, but represents a response to environmental triggers (infection, drugs, or other agents) in genetically predisposed individuals. 1 Smoking paradoxically decreases the risk of UC (unlike Crohn's disease where it increases risk). 1

Cardinal Clinical Features

The cardinal symptom of UC is bloody diarrhea. 1 Associated symptoms include:

• Colicky abdominal pain 1
• Rectal urgency and tenesmus 1, 2
• Mucus in stool 2
• Fecal incontinence 3
• Nocturnal diarrhea 3

Systemic symptoms are less common than in Crohn's disease but may include fever, weight loss, malaise, and fatigue. 1, 3

Disease Extent Classification

UC is classified by anatomic extent using the Montreal classification: 1, 4

• E1 (Proctitis): Limited to the rectum
• E2 (Left-sided colitis): Extends to the splenic flexure
• E3 (Extensive colitis): Extends proximal to the splenic flexure
• E4 (Pancolitis): Extends proximal to the hepatic flexure, affecting the entire colon 4

Pancolitis affects 20-40% of UC patients and carries the highest 10-year colectomy rate at 19% and the greatest colorectal cancer risk. 4

Diagnostic Approach

A gold standard for UC diagnosis does not exist—it requires the combination of clinical presentation, endoscopic findings with histopathology, and exclusion of infectious causes. 1

Endoscopic Features

The diagnosis requires sigmoidoscopy or colonoscopy demonstrating continuous, confluent inflammation starting at the anal verge with: 1

• Loss of normal vascular pattern
• Granularity and erythema
• Mucosal friability
• Spontaneous bleeding
• Erosions and ulcerations in severe cases

Histopathological Confirmation

Biopsies from at least five sites around the colon (including rectum) and ileum are required. 1 Key microscopic features include: 1

• Basal plasmacytosis (earliest diagnostic feature with highest predictive value) 1
• Crypt architectural distortion and decreased crypt density
• Diffuse transmucosal inflammatory infiltrate
• Cryptitis and crypt abscesses
• Absence of granulomas (which suggest Crohn's disease)

Essential Investigations

Initial workup must include: 1

• Full blood count (may show anemia, thrombocytosis, or leucocytosis)
• C-reactive protein and ESR
• Electrolytes, liver and renal function
• Fecal calprotectin
• Stool cultures to exclude infectious pathogens, specifically C. difficile toxin 1
• Immunization status assessment 3

Disease Course and Prognosis

UC follows a relapsing-remitting course, with approximately 50% of patients experiencing a relapse in any given year. 1 The disease carries: 1, 5

• Slight excess mortality in the first two years after diagnosis
• 20-30% of pancolitis patients ultimately require colectomy
• 4.5% risk of colorectal cancer after 20 years of disease duration
• 1.7-fold higher colorectal cancer risk compared to general population 5
• Life expectancy approximately 5 years shorter than people without UC 5

Approximately 20% of patients experience acute severe UC requiring hospitalization during their disease course, which remains a potentially life-threatening condition. 1, 6

Extraintestinal Manifestations

Approximately 27% of UC patients develop extraintestinal manifestations, including: 3, 5

• Inflammatory arthropathies
• Primary sclerosing cholangitis (most clinically important)
• Skin lesions (erythema nodosum, pyoderma gangrenosum)
• Eye inflammation (uveitis, episcleritis)

Critical Pitfalls

Always exclude infectious causes, particularly C. difficile and Cytomegalovirus, during disease flares, as these can mimic or exacerbate UC. 3 Testing should be repeated with every flare. 1

The macroscopic extent at colonoscopy may underestimate true disease extent compared with histology—biopsies are essential for accurate risk stratification for dysplasia surveillance. 4 Classification should always reflect the maximal extent ever documented, even if inflammation regresses with treatment. 4