Ulcerative Colitis vs Crohn’s Disease | IBD

Introduction
There are two main types of idiopathic inflammatory bowel disease (IBD) – ulcerative colitis and Crohn’s disease.
Although both share many similarities in the signs, symptoms and pharmacological management, key distinctions can be made from the location of the inflammation and the histopathological findings.
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Ulcerative colitis
Ulcerative colitis is a chronic inflammatory disease with a relapsing-remitting course. The disease is localised to the colon, with the rectum being the most commonly affected site.1
The underlying aetiology isn’t clear, but it is thought to be linked to environmental and epigenetic factors, including a positive family history.2 Smoking is thought to protect against developing ulcerative colitis.3
Clinical features
Clinical features of ulcerative colitis include:1

Diarrhoea (often bloody ± mucus)
Faecal urgency/incontinence
Tenesmus
Abdominal pain (often felt in the LLQ) and bloating
Fatigue/malaise
Anorexia
Fever
Weight loss

Extra-intestinal manifestations of UC
Extra-intestinal manifestations can be present in up to 30% of patients and include:1,4

Musculoskeletal conditions: pauci-articular arthritis, enthesitis, tenosynovitis, dactylitis
Ophthalmological conditions: episcleritis, scleritis, uveitis
Bone disease: osteopenia, osteomalacia and osteoporosis
Skin lesions: erythema nodosum, pyoderma gangrenosum, aphthous mouth ulcers
Hepatobiliary conditions: primary sclerosing cholangitis, gallstones, autoimmune hepatitis
Haematological conditions: thromboembolism, anaemia

Investigations
Relevant blood tests include:1,5

Relevant stool tests include:

Faecal calprotectin: raised in inflammatory bowel disease but not irritable bowel syndrome (IBS)
Stool microscopy and culture (screen for Clostridium difficile toxin and other infectious microorganisms)

Diagnosis
Ulcerative colitis is usually diagnosed with endoscopic imaging and a biopsy. Options include:5

Flexible sigmoidoscopy: imaging is limited to the distal colon but requires less bowel preparation than a colonoscopy
Colonoscopy: may be required if disease extends more proximally
Abdominal X-ray: sometimes requested to screen for bowel obstruction or toxic megacolon
CT scan with contrast: may be considered to rule out other pathologies and diagnoses

Histology
Histopathological analysis in ulcerative colitis shows:6,7

Continuous inflammation that does not extend beyond the colonic submucosa
Erythema ± ulceration
Crypt abscesses and neutrophil infiltration
Depleted colonic goblet cells
Inflammatory polyps

Management
Management is broadly divided into inducing remission and maintaining remission.
Pharmacological options include:1

Aminosalicylates (e.g. mesalazine and sulfasalazine)
Corticosteroids (can be given topically, orally or intravenously)
Calcineurin inhibitors (e.g. tacrolimus or ciclosporin)
Immunosuppressants (e.g. thiopurines or methotrexate)
Biologics (e.g. infliximab and adalimumab)

Surgical management
There are a few different options for surgery, including a subtotal colectomy with ileostomy, colectomy with ileo-rectal anastomosis, proctocolectomy with ileostomy and restorative proctocolectomy with ileo-anal pouch.8

Crohn’s disease
Like ulcerative colitis, Crohn’s disease is a relapsing-remitting chronic inflammatory disease of the gastrointestinal tract.
However, Crohn’s disease can affect any part of the gastrointestinal tract.9
Again, the aetiology of Crohn’s disease is thought to be linked to a mix of genetic factors, including a positive family history and environmental/lifestyle factors, with smoking being one of the key risk factors.10,11
Clinical features
Clinical features of Crohn’s disease include:9,12

Persistent diarrhoea (may be bloody ± mucus ± pus)
Abdominal pain (RLQ pain/mass may be reported if terminal ileum affected)
Tenesmus
Fever
Malaise/fatigue
Anorexia
Aphthous ulcers
Perianal lesions (fissures, abscesses, fistulas)
Weight loss/faltering growth

Extra-intestinal manifestations of Crohn’s disease
Extra-intestinal manifestations of Crohn’s disease include:9

Musculoskeletal: pauci-articular arthritis (most common extra-intestinal symptom), enthesitis, tenosynovitis, dactylitis
Skin: erythema nodosum, aphthous mouth ulcers, psoriasis, pyoderma gangrenosum
Eyes: episcleritis, uveitis
Bone disease: osteopenia, osteomalacia and osteoporosis
Hepatobiliary conditions: gallstones, primary sclerosing cholangitis

Investigations
Relevant blood tests include:9,12

Full blood count: may show anaemia, leukocytosis and/or thrombocytosis
Urea & electrolytes: as a baseline
Liver function tests: surveillance for primary sclerosing cholangitis
Vitamin B12, vitamin D and folate
CRP/ESR
Iron studies: may show iron deficiency
Coeliac screen: to exclude this as a diagnosis
Yersinia enterocolitica serology: important to exclude

Relevant stool tests include:

Faecal calprotectin: raised in inflammatory bowel disease but not irritable bowel syndrome (IBS)
Stool microscopy and culture (screen for Clostridium difficile toxin and other infectious microorganisms)

Diagnosis
Diagnosis is normally achieved with a colonoscopy with multiple biopsies.9,12
Other imaging options include:

MRI of the abdomen/pelvis
CT abdomen: helps look for other features, including abscesses and fistulas
Abdominal X-ray: can visualise bowel loop distension and rule out other pathologies
Abdominal/pelvic ultrasound

Histology
Histopathological analysis in Crohn’s disease shows:13,14

Transmural inflammation
Cobblestone appearance of the mucosa
Non-caseating granulomas
Skip lesions (due to patchy distribution of inflammation)

Management
Again, management focuses on inducing and maintaining remission.
Pharmacological options include:9

Corticosteroids
Immunosuppressants (e.g thiopurines or methotrexate)
Biologics (e.g infliximab and adalimumab)
Aminosalicylates (e.g mesalazine and sulfasalazine)

Surgical management15
There are several different options for surgery, including strictureplasty, ileocaecal resection, a segmental colectomy, right hemicolectomy, subtotal colectomy with ileostomy, colectomy with ileorectal anastomosis and proctocolectomy with ileostomy.
As Crohn’s disease can affect the entire gastrointestinal tract, surgery is not curative but can greatly improve symptoms.

Summary table
Table 1. Table displaying the key differences between ulcerative colitis and Crohn’s disease

 
Ulcerative colitis
Crohn’s disease

Clinical features

Persistent diarrhoea (often bloody ± mucus)
Abdominal pain (LLQ)
Tenesmus
Faecal urgency/incontinence
Fatigue/malaise
Weight loss

Diarrhoea (sometimes bloody ± mucus ± pus)
Abdominal pain (RLQ)
Tenesmus
Faecal urgency/incontinence
Fatigue/malaise
Weight loss/faltering growth
Perianal lesions
Aphthous ulcers

Location of disease
Colon (most commonly affected area is the rectum)
Entire GI tract (most commonly affected area is the ileum)

Histopathology

Continuous inflammation that does not extend beyond colonic submucosa
Erythema ± ulceration
Crypt abscesses and neutrophil infiltration
Depleted goblet cells
Inflammatory polyps

Transmural inflammation
Cobblestone appearance of mucosa
Non-caseating granulomas
Skip lesions

Treatment options

Aminosalicylates
Corticosteroids
Calcineurin inhibitors
Immunosuppressants
Biologics
Surgery (can be curative)

Aminosalicylates
Corticosteroids
Immunosuppressants
Biologics
Surgery (not curative)

References

NICE CKS. Ulcerative colitis [Internet]. NICE. 2020. Available from: [LINK]
Childers RE, Eluri S, Vazquez C, Weise RM, Bayless TM, Hutfless S. Family history of inflammatory bowel disease among patients with ulcerative colitis: A systematic review and meta-analysis. Journal of Crohn’s and Colitis. 2014 Nov;8(11):1480–97.
Guslandi. Nicotine treatment for ulcerative colitis. British Journal of Clinical Pharmacology [Internet]. 2001 Dec 24;48(4):481–4. Available from: [LINK]
Lynch WD, Hsu R. Ulcerative colitis [Internet]. Nih.gov. StatPearls Publishing; 2022. Available from: [LINK]
BMJ Best Practice. Ulcerative colitis [Internet]. bestpractice.bmj.com. 2023 [cited 2023 Dec 20]. Available from: [LINK]
DeRoche TC, Xiao SY, Liu X. Histological evaluation in ulcerative colitis. Gastroenterology Report. 2014 Aug 1;2(3):178–92.
Singh V, Johnson K, Yin J, Lee S, Lin R, Yu H, et al. Chronic Inflammation in Ulcerative Colitis Causes Long-Term Changes in Goblet Cell Function. Cellular and Molecular Gastroenterology and Hepatology. 2022;13(1):219–32.
Surgery for Ulcerative Colitis [Internet]. Crohnsandcolitis.org.uk. 2022. Available from: [LINK]
NICE CKS. Crohn’s disease [Internet]. NICE. 2020. Available from: [LINK]
Torres J, Gomes C, Jensen CB, Agrawal M, Ribeiro-Mourão F, Jess T, et al. Risk Factors for Developing Inflammatory Bowel Disease Within and Across Families with a Family History of IBD. Journal of Crohn’s and Colitis. 2022 Aug 9;17(1).
Ss M, Ks M, Re S, Ca H, S G. Smoking and Inflammatory Bowel Disease: A Meta-Analysis [Internet]. Mayo Clinic proceedings. 2006. Available from: [LINK]
BMJ Best Practice. Crohn’s disease [Internet]. bestpractice.bmj.com. 2023 [cited 2023 Dec 18]. Available from: [LINK]
McDowell C, Farooq U, Haseeb M. Inflammatory Bowel Disease [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2023. Available from: [LINK]
Ranasinghe IR, Hsu R. Crohn Disease [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022. Available from: [LINK]
Surgery for Crohn’s Disease [Internet]. crohnsandcolitis.org.uk. 2022. Available from: [LINK]