Crohn’s Disease

Original Author: Sittiga Hassan
Last Updated: November 17, 2016
Revisions: 49

Crohn’s disease (CD) is a type of chronic inflammatory bowel disease, along with Ulcerative Colitis

The prevalence of the condition is about 150 per 100,000 people in the UK (less common than ulcerative colitis) and has a peak age of presentation between 15-30 years, and another peak in late adulthood at 60-80 years.

The disease typically follows a remitting and relapsing course. Severe exacerbations may be life-threatening, resulting in severe systemic upset, bowel perforation or obstruction, and even death.


CD can affect any part of the gastrointestinal tract (from mouth to anus) but most commonly targets the distal ileum or proximal colon, yet much of its aetiology still remains unknown. Much like ulcerative colitis, Corhn’s disease appears to have a familial link, however unlike ulcerative colitis smoking increases your risk of developing the condition.

It is characterised by transmural inflammation (affecting all layers of the bowel) in the affected region of bowel, producing deep ulcers and fissues (a ‘cobblestone’ appearance’). The inflammation is not continuous, forming skip lesions throughout the bowel. The microscopic appearance of Crohn’s disease is non-caseating granulomatous inflammation.

Ulcerative Colitis Crohn’s Disease
Site Involvement Large bowel Entire GI tract
Inflammation Mucosa only Transmural
Microscopic Changes Crypt abscess formation

Reduced goblet cells


Granulomatous (non-caseating)
Macroscopic Changes Continuous inflammation (proximal from rectum)

Pseudopolyps and ulcers may form


Discontinuous inflammation (‘skip lesions’)

Fissures and deep ulcers (‘cobblestone appearance’)

Fistula formation

Table 1 – Characteristic Features of Inflammatory Bowel Disease

Due to the transmural nature of the inflammation, fistula can form from affected bowel to adjacent structures, resulting in fistula formation including perianal fistula (54%), entero-enteric fistula (24%), recto-vaginal (9%), entero-cutaneous fistula, or entero-vesica or fistula.

Risk Factors

The aetiology of Crohn’s disease is unknown; yet both environmental factors and genetic factors are thought to play a role. The main risk factors for Crohn’s disease include:

  • Family history – 20% have first degree relative affected.
  • Smoking – increases the risk of developing Crohn’s disease and risk of relapse.
  • White European descent – particularly Ashkenzi Jews.
  • Appendicectomy – increases the risk of developing Crohn’s disease directly after the surgery.

Clinical Features

Crohn’s disease typically presents with episodic abdominal pain and diarrhoea. The abdominal pain may be colicky in nature and will vary in site depending on the region of bowel involved. Diarrhoea is often chronic and may contain blood. The episodes often come in attacks before entering remission.

Fig 1 - Aphthous oral ulcer in active Crohn's disease

Fig 1 – Aphthous oral ulcer in active Crohn’s disease

Systemic symptoms include malaise, anorexia and low-grade fever. It may also result in malabsorption and malnourishment if severe (in children, this may initially present as a failure to grow or thrive).

As the disease affects the entire GI tract, both oral and perianal involvement are common:

  • Oral aphthous ulcers – can be painful and recurring.
  • Perianal disease – can present as skin tags, perianal abscesses, fistulae, or bowel stenosis.

Examination features include abdominal tenderness and distention, mouth or perianal lesions and signs of malabsorption or dehydration (they are often thin). Patients should also be examined for extra-intestinal features.

Extra-Intestinal Features

Crohn’s disease, much like ulcerative colitis, is associated with extra intestinal manifestations of disease:

  • Musculoskeletal – Enteropathic arthritis (typically affecting sacroiliac and other large joints), nail clubbing, or metabolic bone disease (secondary to malabsorption).
  • Skin
    • Erythema nodosum  – tender red/purple subcutaneous nodules, typically found on the patient’s shins.
    • Pyoderma gangrenosum – erythematous papules/pustules which develop into deep ulcers, which can occur anywhere (yet also typically affect the shins).
  • Eyes – Episcleritis, anterior uvetitis, or iritis
  • Hepatobiliary – Primary sclerosing cholangitis (more associated with UC), cholangiocarcinoma (due to association with primary sclerosing cholangitis), and gallstones.
  • Renal: Renal stones (reduced absorption of bile salts which leads to increased free oxalate)
Fig 2 - Extra-intestinal manifestation of Crohn's disease: (A) Erythema nodosum (B) Pyoderma gangrenosum

Fig 2 – Extra-intestinal manifestation of Crohn’s disease: (A) Erythema nodosum (B) Pyoderma gangrenosum


Routine bloods are required to examine for anaemia, low albumin (secondary to malabsorption), and raised CRP and WCC. Liver function tests may become deranged in patients on treatment.

NICE guidelines recommend that faecal calprotectin testing is carried out in patents with recent onset lower gastrointestinal symptoms: it is raised in inflammatory bowel disease, but unchanged in irritable bowel syndrome. A stool sample sent for MC&S for any potential infective cause can be considered,

Fig 3 - Endoscopic image of Crohn's colitis showing deep ulceration

Fig 3 – Endoscopic image of Crohn’s colitis showing deep ulceration

There are three main types of imaging that can be utilised in the diagnosis of Crohn’s disease:

  • Colonoscopy with biopsy – the gold standard. A characteristic macroscopic finding is cobblestoning of the bowel (fissures and ulcers separate islands of healthy mucosa), with a non-caseating granulomatous inflammation.
  • Barium swallow – less commonly performed, yet can show strictures, ‘rose thorn’ ulcers, and the ‘string sign of Kantor’.
  • CT scan – usually warranted in severe Crohn’s disease, which may demonstrate bowel obstruction, perforation, collection formation, or fistulae.

For perianal disease, pelvic MRI is first line as it is both accurate and non-invasive. Examination under anaesthesia with proctosigmoidoscopy may also be considered to examine for concomitant rectosigmoid inflammation.

In the acute situation, an abdominal radiograph (AXR) may be useful to demonstrate toxic megacolon or bowel obstruction.


Patients with suspected IBD should be referred to a gastroenterologist for confirmation of the diagnosis and initiation of treatment; those with acute severe disease should be admitted on an emergency basis. Anti-motility drugs, such as loperamide, should be avoided in acute attacks, as these can precipitate toxic megacolon.

Inducing Remission

The medical management to induce remission in Crohn’s Disease typically requires either sulphasalazine or methotrexate alongside oral prednisolone. Azathioprine may also be additionally used as a steroid-sparing agent.

Any acute attacks will also warrant aggressive fluid resuscitation, nutritional support, and prophylactic heparin (due to prothrombotic state of IBD).

Maintaining Remission

Azathioprine or mercaptopurine are recommended as a monotherapy to maintain remission. Methotrexate can be considered in those who have used it to induce their remission or cannot tolerate other maintenance therapies.

In recent years with the development of biological agents, patients can be started on infliximab, adalumimab, or rituximab if there has been a failure of treatment with other agents.

Smoking cessation is advised. Due to increased risk of colorectal malignancy, colonoscopic surveillance is offered to people who have had the disease for >10 years with >1 segment of bowel affected (follow-up time frame depends on risk stratification of disease following initial endoscopy).

Further Management

Patients should be referred to IBD-nurse specialists and patient support groups. Enteral nutritional support should be considered in young patients with growth concerns, with close support from nutritional team.

Antibiotics are only offered to those with obvious concurrent infection or perianal disease (typically ciprofloxacin or metronidazole).

Surgical Management

70-80% of Crohn’s patients require surgery at some point. Surgical intervention is indicated in those with failed medical management, severe complications (such as strictures or fistulas), or growth impairment in younger patients.

The most common procedure is ileocaecal resection; removal of terminal ileum and caecum, with primary anastamosis between ileum and ascending colon. Various other surgical procedures may be used – but a bowel-sparing approach must always be taken to prevent short gut syndrome in later years.



  • Stricture formation
    • Inflammation of the bowel can result in stricture formation, resulting in bowel obstruction and perforation.
  • Fistula
    • In patients with Crohn’s Disease, fistula such as enterovesical (presenting with recurrent UTIs and pneumaturia), enterocutaneous, or rectovaginal fistula can form.
    • Fistulas can be removed by fistulotomy (i.e. opening the tract up) or Seton technique (where a cord is tied around the fistula which keeps the fistula open and over time the fistula drains and eventually heals over).
  • Perianal complications
    • Common in patients with Crohn’s Disease and can include formation of abscesses or fistula.
  • GI malignancy
    • Patient’s with Crohn’s disease have about a 3% risk of developing colorectal cancer over 10 years.
    • Small bowel cancer is about 30x more common in those with Crohn’s disease than the general population.


  • Malabsorption
    • Including growth delay in children.
  • Osteoporosis
    • Secondary to malabsorption or long-term steroid use.
  • Increased risk of gallstones
    • Due to reduced reabsorption of bile salts at inflamed terminal ileum.
  • Increased risk of renal stones
    • Due to malabsorption of fats in the small bowel which causes calcium to remain in the lumen. Oxalate is then absorbed freely (as normally bound to calcium and excreted in stool), resulting in hyperoxaluria and formation of oxalate stones in the renal tract.

Further Reading

Crohn's Disease
Baumgart DC. The Lancet

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