Inflammatory Bowel Disease

The Concept

Inflammatory bowel disease (IBD) comprises two chronic, relapsing, immune-mediated conditions — ulcerative colitis (UC) and Crohn's disease (CD). The whole topic becomes manageable once two distinguishing principles are grasped: where the disease occurs and how deep it goes. UC is confined to the colon and is superficial (mucosal); Crohn's can affect anywhere from mouth to anus and is transmural. Almost every clinical difference flows from these two facts.

The Key Comparison

Clinical Features

UC characteristically causes bloody diarrhoea with mucus, urgency and tenesmus. Crohn's causes abdominal pain, diarrhoea (often non-bloody), weight loss and perianal disease (fissures, fistulae, abscesses), reflecting its transmural, patchy nature. Both may have extraintestinal manifestations — arthritis, uveitis/episcleritis, erythema nodosum, pyoderma gangrenosum, aphthous ulcers, and (in UC) primary sclerosing cholangitis.

Investigation

Colonoscopy with biopsy establishes the diagnosis and distribution; stool tests exclude infection and measure faecal calprotectin (a marker of gut inflammation); bloods assess anaemia and inflammation. In Crohn's, MRI (small bowel and pelvis) maps disease extent, strictures and fistulae.

Management

• Medical — 5-aminosalicylates (mesalazine) especially for UC; corticosteroids to induce remission in a flare; immunomodulators (azathioprine, methotrexate) and biologics (anti-TNF, e.g. Infliximab) to maintain remission; nutritional therapy (important in Crohn's).
• Surgery in UC — a colectomy is curative and is indicated for disease refractory to medical therapy, dysplasia/cancer, or acute complications (toxic megacolon).
• Surgery in Crohn's — not curative and used only for complications (strictures, fistulae, abscesses), with conservative, bowel-preserving resections because disease recurs and repeated resection risks short-bowel syndrome.

Acute Severe Colitis — an Emergency

A vital point is that IBD can present as an acute emergency. Acute severe ulcerative colitis (bloody diarrhoea with systemic upset) can progress to toxic megacolon — a dilated, thin-walled, non-contractile colon at risk of perforation. It is monitored closely (stool frequency, abdominal X-rays, inflammatory markers) and treated with intravenous steroids and rescue therapy; failure to improve within a few days, or perforation, mandates an emergency colectomy. Recognising this scenario is life-saving.

Surgery in Detail

The contrasting surgical philosophies deserve emphasis. In UC, because the disease is limited to the colon, removing the colon and rectum is curative — a restorative proctocolectomy with an ileo-anal pouch, or a panproctocolectomy with an end ileostomy. In Crohn's, because disease can recur anywhere, surgery is never curative and is kept minimal (stricturoplasty, limited resection) to preserve bowel length and avoid short-bowel syndrome from repeated operations.

Cancer Risk & Surveillance

Long-standing colonic IBD (particularly extensive UC, and Crohn's colitis) carries an increased risk of colorectal cancer, arising from areas of dysplasia rather than discrete polyps. Patients therefore enter surveillance colonoscopy programmes after several years of disease, and the finding of dysplasia may itself be an indication for colectomy — a key reason IBD is followed lifelong even when symptoms are controlled.

Extraintestinal Disease & Nutrition

The extraintestinal manifestations deserve emphasis because they may dominate the picture or even precede the bowel disease. Some track disease activity (erythema nodosum, peripheral arthritis, episcleritis), while others run an independent course (primary sclerosing cholangitis and ankylosing spondylitis, associated particularly with UC). Nutritional consequences are important in Crohn's, where transmural small-bowel disease and resections cause malabsorption, weight loss, anaemia and (with terminal ileal disease) vitamin B12 and bile-salt malabsorption — so nutritional assessment and support are integral to care.

• UC: mucosal, continuous, colon only; crypt abscesses; colectomy is curative; smoking protective.
• Crohn's: transmural, skip lesions, mouth-to-anus; non-caseating granulomas; fistulae/strictures; surgery not curative; smoking worsens.
• Medical ladder: 5-ASA → steroids (flare) → immunomodulators → biologics (anti-TNF).

Transmural inflammation explains Crohn fistulae and strictures.

• IBD = chronic relapsing immune-mediated disease: UC (mucosal, colon only, continuous) vs Crohn's (transmural, mouth-to-anus, skip lesions).
• UC: bloody diarrhoea + mucus, urgency, tenesmus; crypt abscesses, no granulomas; toxic megacolon; higher cancer risk; PSC; smoking protective.
• Crohn's: pain, weight loss, perianal disease; non-caseating granulomas; fistulae/strictures/abscesses; smoking worsens.
• Diagnose with colonoscopy + biopsy, faecal calprotectin, MRI (Crohn's); exclude infection.
• Medical: 5-ASA, steroids, immunomodulators, biologics; surgery curative in UC (colectomy) but not in Crohn's (bowel-preserving, for complications).