Inflammatory Bowel Disease: Crohn's Disease and Ulcerative Colitis

Inflammatory Bowel Disease: Crohn's Disease and Ulcerative Colitis

Inflammatory bowel disease (IBD) is an umbrella term for two closely related but distinct chronic relapsing-remitting conditions: Crohn's disease (CD) and ulcerative colitis (UC). Both involve dysregulated immune activation against the gut microbiome in genetically susceptible individuals, causing chronic, often debilitating gut inflammation. A third category — IBD unclassified (IBDU) — is used when the distinction between CD and UC cannot be made.

IBD affects approximately 10 million people worldwide, with the highest prevalence in Western industrialised countries (Northern Europe, North America, Australia). Incidence is rising rapidly in East Asia — including China, Japan, and South Korea — as westernisation of diet and lifestyle alters the gut microbiome and immune programming. China's IBD caseload has grown approximately 10-fold over the past two decades.

IBD typically first presents in the teens to 30s (although a second peak occurs at 50–70), affects men and women equally, and follows a lifelong relapsing-remitting course. With effective modern management, most patients can achieve sustained remission and lead full lives.

Crohn's Disease vs Ulcerative Colitis

Feature	Crohn's Disease	Ulcerative Colitis
Location	Anywhere from mouth to anus; most commonly terminal ileum + colon	Colon only; typically involves the rectum and extends continuously proximally; rectal sparing can occur
Inflammation depth	Transmural (full thickness of bowel wall)	Mucosal only (superficial)
Pattern	Patchy, with skip lesions (normal bowel between affected segments)	Continuous, confluent
Strictures	Common (transmural fibrosis)	Rare
Fistulas/abscesses	Characteristic (transmural inflammation tracks through)	Very rare
Perianal disease	Common (fistulas, fissures, skin tags)	Rare
Smoking	Smoking worsens Crohn's disease outcomes; stopping is recommended	Associations with UC differ from Crohn's, but smoking is not a treatment; stopping is recommended with clinical support
Rectal bleeding	Variable	Common, but not present in every patient or at every stage
Surgery	Frequent (recurrence after surgery common)	Removal of both colon and rectum eliminates colonic/rectal UC; surgery and pouch-related follow-up may still be needed

What Causes IBD?

IBD results from a complex interaction of genetic susceptibility, gut microbiome dysbiosis, environmental triggers, and dysregulated immune response:

Genetics: >200 genetic loci are associated with IBD susceptibility. Key genes affect innate immunity, autophagy (NOD2, ATG16L1), and epithelial barrier function. Having an affected first-degree relative increases IBD risk 4–10×.

Gut microbiome: IBD is associated with reduced gut bacterial diversity and specific microbial imbalances (dysbiosis). Particular bacterial species may trigger pathological immune activation in susceptible individuals.

Environmental factors: Westernised diet (high fat, refined carbohydrates, low fibre), antibiotic use in early life, C-section delivery, reduced childhood infections, urban living — all associated with increased IBD risk. These factors may alter the gut microbiome and immune education in early life.

Immune dysregulation: In IBD, T-helper cells (particularly Th1 and Th17 subsets) are inappropriately activated against gut antigens, driving persistent mucosal inflammation. This is why biological therapies that block specific immune pathways (TNF-α, IL-12/23, integrins) are so effective.

Symptoms

Ulcerative Colitis

• Rectal bleeding — the cardinal symptom; blood mixed with or coating the stool
• Diarrhoea — urgency, frequency (up to 20 motions/day in severe disease), tenesmus (sensation of incomplete evacuation)
• Lower abdominal cramping — particularly before defecation
• Disease extent and activity are assessed separately: proctitis affects the rectum and can cause bleeding with constipation; left-sided colitis can cause diarrhoea and bleeding; pancolitis involves the whole colon. Extent informs management, but severity also depends on symptoms, inflammatory activity, disease course and impact; extensive disease is not automatically the most severe.

Severe acute colitis (SAC) / fulminant colitis:

• ≥6 bloody stools/day + one of: fever, tachycardia, anaemia, or elevated ESR/CRP
• Requires hospitalisation; risk of toxic megacolon and colonic perforation — a surgical emergency

Crohn's Disease

Symptoms depend on disease location:

Ileocolonic Crohn's (most common):

• Right lower quadrant abdominal pain — may mimic appendicitis
• Diarrhoea (without blood if small bowel predominates; with blood if colonic)
• Weight loss — malabsorption (small bowel disease) + reduced intake
• Fatigue and anaemia

Colonic Crohn's: similar to UC — diarrhoea, bleeding, urgency

Upper GI Crohn's: nausea, vomiting, dysphagia, heartburn

Perianal Crohn's:

• Complex fistulas (connections between bowel and skin, vagina, or bladder)
• Anal fissures resistant to healing
• Perianal abscesses
• Skin tags around the anus
• Often painful and significantly impairs quality of life

Extraintestinal Manifestations (EIM)

Both CD and UC may affect organs outside the gut — in approximately 25–40% of patients:

• Joints: IBD-associated arthropathy (peripheral joint pains correlated with bowel activity; axial arthritis/sacroiliitis independent of bowel activity; ankylosing spondylitis)
• Eyes: uveitis, episcleritis (eye redness and pain)
• Skin: erythema nodosum (tender red nodules on shins); pyoderma gangrenosum (painful ulcers)
• Liver: primary sclerosing cholangitis (PSC) — associated particularly with UC, but also occurs with CD and without IBD; progressive bile duct scarring; raises risk of cholangiocarcinoma and colorectal cancer

Diagnosis

Colonoscopy with Biopsies

The cornerstone of IBD diagnosis — allows direct visualisation of the mucosa, assessment of extent and activity, and tissue sampling. Colonoscopy in UC shows continuous erythema, loss of vascular pattern, granularity, and ulceration from the rectum proximally. Crohn's shows patchy inflammation, cobblestoning, deep ulcers, and skip lesions.

Histology on biopsies helps distinguish IBD from other causes and characterise its type. Non-caseating granulomas can support Crohn's disease in the appropriate clinical setting, but are not specific to it; infections and other causes must be considered alongside the endoscopic, imaging and clinical findings.

MRI Enterography (MRE)

The preferred investigation for small bowel Crohn's disease — provides detailed imaging of the entire small bowel, assessing:

• Location and extent of active inflammation (mural thickening, mucosal hyperenhancement)
• Complications: strictures, abscesses, fistulas
• Perianal disease (pelvic MRI)

No radiation exposure — important as IBD is a lifelong disease requiring repeated imaging.

Laboratory Markers

• CRP and ESR — elevated during active disease; guide treatment response
• Faecal calprotectin — a marker of intestinal inflammation used alongside symptoms, prior findings and other tests to guide monitoring. A low result does not by itself establish remission, and an elevated result is not specific for active IBD. Interpretation and any need for endoscopy or imaging depend on disease location, clinical context and the assay; do not change treatment from a single value alone.
• FBC: anaemia (blood loss, chronic disease, B12/folate deficiency in ileal CD), leucocytosis, thrombocytosis
• Albumin: low in active disease — reflects protein loss and inflammation
• IBD serology (ASCA, ANCA): moderate diagnostic utility for differentiating CD from UC; not used in isolation

Stool Cultures

New or worsening diarrhoea in suspected or established IBD should prompt infection assessment, including stool cultures and C. difficile testing; parasitology is guided by travel, exposure history and clinical suspicion. Samples should be obtained promptly, with treatment timing decided by the treating team rather than a blanket requirement to await every result. Acute severe ulcerative colitis requires urgent hospital specialist care: BSG guidance advises that indicated corticosteroid treatment should not be delayed while awaiting stool culture and C. difficile results. Suspected or confirmed infection needs assessment and any appropriate concurrent treatment.

Treatment

Treatment aims are: inducing and maintaining remission; preventing complications (strictures, fistulas, cancer); minimising steroid use; and improving quality of life.

5-Aminosalicylic Acid (5-ASA / Mesalazine)

Mesalazine (mesalamine, 5-ASA) is a standard treatment for mild-to-moderate UC. The formulation must match the extent of inflammation: suppositories principally treat the rectum (proctitis); disease extending further may need an appropriate enema or foam formulation and/or oral treatment. A suppository alone should not be assumed to cover left-sided colitis. Observational studies associate 5-ASA use with a lower colorectal cancer risk in colonic IBD, but do not establish a cancer-prevention effect independent of inflammation control. Treatment does not replace risk-based colonoscopic surveillance.

Drug-specific recommendations for Crohn’s disease differ from those for UC. Oral mesalamine is not recommended for induction or maintenance in mild-to-moderately active Crohn’s disease. The 2025 ACG guideline allows sulfasalazine to be considered only for symptomatic mild colonic Crohn’s disease; this limited role does not establish effectiveness for isolated small-bowel disease, maintenance of remission or all 5-ASA preparations. A gastroenterologist selects treatment for the disease location and severity.

Corticosteroids

Corticosteroids can be used for induction of remission; the choice depends on disease severity, location and formulation:

• Oral prednisolone: typically 40 mg/day tapering over 8–12 weeks; effective for rapid symptom control; not suitable for maintenance (bone loss, metabolic effects, adrenal suppression)
• IV hydrocortisone or methylprednisolone: for severe/hospitalised flares
• Budesonide formulations differ: Entocort EC is used for mild-to-moderate active Crohn’s disease involving the ileum and/or ascending colon. Budesonide MMX extended-release tablets are used to induce remission in active mild-to-moderate ulcerative colitis. These are formulation- and indication-specific options, not interchangeable treatments chosen simply because UC extends to the right colon. Steroid adverse effects and local product approval still require consideration.

Prolonged steroid use or steroid dependence mandates escalation to steroid-sparing therapies.

Immunomodulators

For maintenance of remission — steroid-sparing agents:

• Azathioprine / 6-mercaptopurine: inhibit purine synthesis in lymphocytes; effective maintenance therapy in both CD and UC; onset of action 3–6 months; risk of myelosuppression and lymphoma with long-term use; check TPMT enzyme before starting
• Methotrexate: used in CD; effective maintenance; contraindicated in pregnancy

Biological Therapies

A major advance in IBD treatment — targeted monoclonal antibodies against specific inflammatory pathways:

Anti-TNF agents:

• Infliximab (Remicade/Remsima) — IV infusion every 8 weeks after induction; effective for moderate-to-severe CD and UC; first-line biologic in many guidelines; also effective for perianal fistulas
• Adalimumab (Humira/Hyrimoz) — subcutaneous fortnightly injection; comparable efficacy; convenient for home administration
• Certolizumab pegol — SC injection; used in CD; pegylated fragment with minimal placental transfer. Pregnancy use requires an individual benefit–risk assessment; limited pregnancy data do not establish absence of risk.

Anti-integrin:

• Vedolizumab (Entyvio) — IV or SC; selective for the gut (blocks lymphocyte trafficking into gut mucosa via α4β7 integrin); gut-selective with favourable safety profile; effective in both CD and UC; preferred in elderly or immunocompromised patients where anti-TNF infection risk is a concern

Anti-IL-12/23:

• Ustekinumab (Stelara) — IV loading dose then SC every 8–12 weeks; targets IL-12 and IL-23 (Th1 and Th17 pathway); effective in CD and UC; excellent safety profile; low immunogenicity

Small molecule (JAK inhibitors) — oral:

• Tofacitinib (Xeljanz) — oral twice daily; licensed for UC; rapid onset; risk of thromboembolism and herpes zoster; not for CD
• Upadacitinib (Rinvoq) — selective JAK1 inhibitor; approved for both CD and UC; an effective oral option; comparative efficacy depends on the disease, prior treatment and outcome assessed; once daily tablet; monitoring required

Combination therapy can improve outcomes and reduce anti-drug antibody formation in selected settings, with evidence particularly supporting infliximab plus azathioprine in appropriate patients. Benefits cannot be assumed for every anti-TNF–immunomodulator pairing: methotrexate is not interchangeable with azathioprine in the clinical efficacy evidence. The regimen and duration require assessment of disease, previous treatment, infection and other adverse-effect risks.

Surgery

Ulcerative Colitis:
Proctocolectomy removes the diseased colon and rectum and eliminates UC in those organs. Follow-up is still needed for surgery-related or pouch problems and for any symptoms outside the bowel. Surgery is indicated for:

• Acute severe colitis not responding to medical therapy (toxic megacolon/perforation: emergency surgery)
• Medically refractory disease
• High-grade dysplasia or cancer
• Elective patient choice

For suitable patients, restorative proctocolectomy with ileal pouch-anal anastomosis (IPAA/"J-pouch") creates a reservoir from the terminal ileum connected to the anus, allowing stool to pass through the anus. Continence and pouch function can vary; this is not a guaranteed functional outcome. The surgical team discusses suitability, alternatives such as an ileostomy, risks and the operative approach.

Crohn's Disease:
Surgery in CD treats complications (strictures causing obstruction, fistulas, abscesses) but does not cure the underlying disease — Crohn's recurs at the anastomosis. Principles:

• Bowel-sparing surgery — resect as little as possible; short strictureplasty for short fibrous strictures rather than resection
• Drainage of abscesses (often CT-guided) before definitive surgery
• EUA (examination under anaesthesia) for complex perianal fistulas; loose seton drainage to control sepsis before definitive repair; anti-TNF biologics combined with surgical repair for perianal fistulas

IBD Care in China

China's gastroenterology and IBD centres offer:

• Comprehensive IBD diagnosis: high-definition colonoscopy with biopsies, MRI enterography, faecal calprotectin, and full serological and microbiological panel
• Full biological therapy access: infliximab, adalimumab, vedolizumab, and ustekinumab — including Chinese biosimilar versions; tofacitinib and upadacitinib available
• Infliximab drug level monitoring: therapeutic drug monitoring (TDM) guided dose optimisation — reduces loss of response and guides switching decisions
• Laparoscopic colectomy and J-pouch surgery: experienced colorectal surgeons for IBD-related surgery; minimally invasive approach standard
• Perianal Crohn's management: combined medical and surgical approach with EUA, seton insertion, and biologic therapy
• Cost: care in China is generally less expensive than UK private treatment, but the hospital prices each case individually — ask us for the written quote before you commit.
• Full English care navigation from diagnosis through biological therapy and surgical planning

Contact a PriumCare care navigator to arrange an IBD assessment, colonoscopy, or biological therapy consultation.

---

Medical content based on MSD Manuals and international IBD guidelines (ECCO, AGA, NICE). Evidence reviewed 2025.

Targeted editorial source correction

Editorial source check: 25 October 2026. This update addresses the specific diagnostic and treatment claims documented below; it is not a whole-article medical review. The original publication date is retained.

• ACG preventive care guideline: smoking cessation
• ECCO diagnostic consensus: granulomas and exclusion of infection
• AGA: Crohn’s disease biomarkers
• FDA: Entocort EC prescribing information
• FDA: Uceris extended-release tablet prescribing information

Additional targeted source check: 25 October 2026. The clarifications above concern distribution, symptoms, surgery, severity and specific drug claims, not a whole-article medical review.

• BSG 2025: typical distribution and rectal sparing
• NIDDK: variable UC symptoms
• NIDDK: removal of colon and rectum
• ACG: severity uses symptoms, inflammatory burden, course and impact
• AASLD: PSC and IBD association
• Cimzia prescribing information: pregnancy risk and placental transfer
• AGA: treatment-specific comparative UC efficacy
• AGA Crohn guideline: combination therapy evidence and methotrexate knowledge gap
• AGA: pouchitis and inflammatory pouch disorders after IPAA

Additional targeted source clarification

Editorial source check: 25 October 2026. These changes clarify selected test indications, medicine selection and evidence limits. They are not a whole-article medical review. Original publication date is retained.

• ACG 2025: drug-specific Crohn’s disease recommendations
• ACG official 2025 Crohn’s guideline highlights
• AGA: formulation and disease extent in mild-to-moderate UC
• BSG 2025: IBD surveillance and observational chemoprevention evidence

Targeted infection-testing and urgent-care clarification

Editorial source check: 25 October 2026. This checks only the infection-testing and treatment-timing statement clarified above; it is not a whole-article medical review and adds no named clinical reviewer. The original publication date is retained.

• BSG 2025: infection assessment and acute severe colitis care
• BSG 2019: acute severe colitis and pending stool-test results