Continuous, Superficial, but Not Simple
Ulcerative colitis (UC) is a chronic inflammatory bowel disease confined to the colon and rectum. Two features distinguish it from Crohn's disease: inflammation is limited to the mucosal and submucosal layers (it does not penetrate the full bowel wall), and it extends continuously from the rectum proximally — there are no skip lesions. The extent of involvement categorises UC into proctitis (rectum only — 30 to 50 percent of patients), left-sided colitis (up to the splenic flexure), and extensive/pancolitis (beyond the splenic flexure).
Disease Extent Matters
Extent at diagnosis is one of the strongest predictors of disease course. Proctitis has the mildest course and lowest colectomy risk. Extensive colitis carries the highest risk of complications, hospitalisation, and surgery. However, disease extent is not fixed — approximately 10 to 30 percent of patients with proctitis will experience proximal extension over 10 years. This underscores the importance of monitoring disease extent over time.
Symptoms and Severity
The hallmark symptoms of UC are bloody diarrhoea, urgency, tenesmus (a sensation of incomplete evacuation), and cramping abdominal pain. Severity is assessed using clinical indices (the Mayo Score) that combine stool frequency, rectal bleeding, endoscopic appearance, and physician global assessment. Mild disease may cause only slight increases in stool frequency with intermittent blood. Severe disease involves six or more bloody stools daily, tachycardia, anaemia, and elevated inflammatory markers — potentially requiring hospitalisation.
Extraintestinal Manifestations
Despite being confined to the colon, UC is not purely a gut disease. Up to 40 percent of patients experience extraintestinal manifestations: peripheral arthritis (the most common), primary sclerosing cholangitis (PSC — an association unique to UC), erythema nodosum, pyoderma gangrenosum, uveitis, and venous thromboembolism. Some track with intestinal disease activity (arthritis, skin lesions); others follow an independent course (PSC, uveitis).
Maintenance Therapy Is Non-Negotiable
UC is characterised by relapsing-remitting behaviour. Without maintenance therapy, 70 to 80 percent of patients relapse within one year of achieving remission. This makes ongoing treatment essential — not optional — even when a patient feels well. 5-Aminosalicylates (mesalazine) are effective maintenance therapy for mild-to-moderate disease, with topical (rectal) formulations showing superior efficacy for proctitis and left-sided disease. Immunomodulators, biologics, and small molecules are used for moderate-to-severe disease or when 5-ASA fails.
Cancer Surveillance
Long-standing UC (8 or more years of extensive disease, or 10 or more years of left-sided disease) increases colorectal cancer risk. Surveillance colonoscopy with chromoendoscopy and random biopsies is recommended every 1 to 3 years, depending on risk factors (concomitant PSC, family history, previous dysplasia). Early detection of dysplasia allows timely intervention — either endoscopic resection or colectomy — preventing cancer progression.