Definition
Idiopathic Inflammatory Bowel Diseases (IBD) include Crohn’s disease and ulcerative colitis. Crohn’s disease can affect any part of the gastrointestinal tract, whereas ulcerative colitis is limited to the colon and rectum. Both conditions are characterized by chronic inflammation.

Pathogenesis
The cause of IBD remains unknown, but genetic, environmental, and immune factors are involved. Dysregulation of the immune system leads to intestinal inflammation, often in individuals with a genetic predisposition.

Diagnosis
Diagnosis is based on clinical symptoms such as diarrhea (with or without blood), abdominal pain, and fatigue. The physician confirms the diagnosis through tests such as endoscopy with biopsy and imaging techniques like magnetic enterography. Laboratory markers such as CRP and calprotectin are also helpful.

Treatment
Treatment includes medication (aminosalicylates, corticosteroids, immunosuppressants, biologics), nutritional support, and, if necessary, surgery to manage complications. Personalized follow-up by a specialist gastroenterologist is critical for disease management.

How the two conditions differ

Ulcerative colitis affects the colon only, always begins in the rectum and extends proximally in a continuous fashion, with inflammation limited to the mucosa.

Crohn’s disease can involve any part of the gastrointestinal tract, most often the terminal ileum. Lesions are patchy with healthy segments between them, and inflammation is transmural, involving the full thickness of the wall. This is why Crohn’s disease causes strictures, fistulas and abscesses, which are not features of ulcerative colitis.

Symptoms that point to organic disease

  • Chronic diarrhoea, often with mucus
  • Blood in the stool, more typical of ulcerative colitis
  • Abdominal pain and cramping, more typical of Crohn’s disease
  • Nocturnal stools that wake the patient, a feature that distinguishes IBD from irritable bowel syndrome
  • Fatigue, fever, weight loss, anaemia

Extraintestinal manifestations such as arthritis, eye inflammation, skin lesions and primary sclerosing cholangitis often precede the diagnosis.

Diagnosis

No single test establishes the diagnosis. Colonoscopy with biopsies is the cornerstone, defining extent, pattern and severity. Faecal calprotectin is particularly useful, as it distinguishes organic inflammation from irritable bowel syndrome and is also used in monitoring without repeated endoscopy. Stool cultures exclude infectious colitis, and small bowel imaging is added when Crohn’s disease is suspected.

Treatment and surveillance

Management has two aims: inducing remission and maintaining it. The goal is not only symptom relief but mucosal healing. Options include aminosalicylates, corticosteroids for flares but never for maintenance, immunomodulators, and biologic and targeted agents that have transformed the outlook over the past two decades.

Long-standing extensive colonic inflammation raises the risk of colorectal cancer, so these patients enter a surveillance colonoscopy programme with targeted biopsies, at intervals set by extent, duration and disease activity.

Diagnosis rests on colonoscopy with biopsies. Long standing extensive colonic disease raises the risk of colorectal cancer, which is why surveillance is performed.

Key figures

  • Ulcerative colitis: colon only, continuous, inflammation limited to the mucosa
  • Crohn disease: whole digestive tract, patchy, transmural
  • Faecal calprotectin: raised in IBD, normal in irritable bowel syndrome
  • Nocturnal stools that wake the patient do not occur in irritable bowel syndrome
  • Extensive disease over several years: entry into a surveillance programme with targeted biopsies

Frequently asked questions

What is the difference between Crohn’s disease and ulcerative colitis?

Ulcerative colitis affects the colon only, starts in the rectum and spreads continuously, with inflammation confined to the mucosa. Crohn’s disease can affect any part of the gastrointestinal tract, with patchy lesions and inflammation through the full thickness of the wall, which is why it causes strictures, fistulas and abscesses.

How is IBD distinguished from irritable bowel syndrome?

By features of organic disease: blood in the stool, fever, weight loss, anaemia and above all nocturnal stools that wake the patient, none of which occur in irritable bowel syndrome. Faecal calprotectin is raised in inflammatory bowel disease and normal in a functional disorder. Colonoscopy with biopsies gives the definitive answer.

Why are regular colonoscopies needed?

Because long-standing extensive inflammation of the colon increases the risk of colorectal cancer. Patients with extensive disease of several years duration enter a surveillance programme with targeted biopsies, at intervals determined by the extent, duration and activity of the disease.

Sources


Content last updated: September 2026 (16/09/2026).