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Crohn disease

Last updated: April 9, 2021

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Crohn disease (CD) is an inflammatory bowel disease (IBD), the pathogenesis of which is not fully understood. The clinical presentation of CD may be similar to ulcerative colitis (UC), the other most common IBD. CD mostly affects young adults and adolescents between the ages of 15 and 35. It typically affects the terminal ileum, but can discontinuously affect the entire gastrointestinal tract and commonly leads to complications such as fistulas, abscesses, and stenosis. Clinical features include diarrhea, weight loss, and abdominal pain in the right lower quadrant (RLQ), as well as extraintestinal manifestations in the eyes, joints, or skin. Diagnosis is based on the patient's medical history, physical examination, lab tests, imaging (e.g., MRI), endoscopy, and serological testing. Acute episodes are treated with corticosteroids; immunosuppressants may be indicated in severe cases. Antibiotics and surgical intervention may be needed to help treat complications. As Crohn disease is not localized to a specific region of the GI tract, surgical resection is not a curative option (unlike in UC), and treatment instead focuses on limiting the progression and recurrence of inflammatory episodes.

  • Prevalence: 200 cases per 100,000 population
  • Incidence: ∼ 6 cases per 100,000 population per year [1]
  • Sex: =
  • Typical age of onset: bimodal distribution with one peak at 15–35 years and another one at 55–70 years [2][3]
  • Populations with higher prevalence [4]
    • Individuals of Northern European descent
    • Individuals of Ashkenazi Jewish descent

Epidemiological data refers to the US, unless otherwise specified.

  • Cause: Immune dysregulation and dysbiosis, which promotes chronic inflammation, the ultimate cause of which is not fully understood.
  • Risk factors [4]
    • Active and passive smoking of tobacco
    • Familial aggregation
    • Genetic predisposition (e.g., mutation of the NOD2 gene, HLA-B27 association)

Nicotine consumption is the only (known) controllable risk factor for Crohn disease. Therefore, smoking cessation is especially important in patients with CD.


Inflammation is most likely caused by immune dysregulation.

Abscess and fistula formation

Intestinal aphthous ulcers transmural fissures and inflammation of the intestinal walls → adherence of other organs or the skin penetration of tissue → microperforation and abscess formation → macroperforation into these structures → fistula formation

CD typically occurs episodically with a 30%-risk of recurring inflammation over the span of one year. If symptoms persist for six months, the disease is considered chronic. Without treatment, relapses and complications are to be expected.

Constitutional symptoms [7]

  • Low-grade fever
  • Weight loss
  • Fatigue

Intestinal symptoms [7]

CD most commonly affects the terminal ileum and colon, but involvement of any part of the GI tract (from mouth to anus, except rectum) is possible.

Perianal fistulas and abscesses are often the first signs of Crohn disease.

Extraintestinal symptoms [9]


Diagnosing CD requires the integration of clinical presentation, laboratory tests, and endoscopic, histologic, pathologic and radiologic findings.

  1. If a patient presents with symptoms suggestive of CD, conduct blood tests and stool tests (see “Laboratory tests” below) to rule out other possible causes for bowel inflammation/GI symptoms. [10]
  2. Confirm diagnosis with endoscopy and/or radiographic imaging and/or biopsy.
  3. Perform contrast radiological studies and/or ultrasonography to assess extent, severity, and complications (e.g., abscesses, fistulas, and stenoses)

Laboratory tests

Blood [10]


Imaging [14][15]

Endoscopy [17]

Endoscopy confirms the diagnosis, assesses the extent of the disease, differentiates CD from other diseases (e.g., ulcerative colitis, peptic ulcers, etc.), and may also be used as a therapeutic tool (e.g., dilatation of ducts, intestinal loops).

Crohn disease and ulcerative colitis

Crohn disease

Ulcerative colitis

  • Mediated by dysfunctional IL-23-Th17 signaling
Frequency/type of defecation
  • Increased
  • Typically nonbloody, watery diarrhea
  • May be bloody in more severe cases
Nutritional status
  • Mostly normal, but weight loss and malnutrition may occur in severe disease [18]
Physical examination
  • Mostly constant pain in RLQ
  • Palpable abdominal mass
  • Low-grade fever
Extraintestinal manifestations
  • Rare
Other complications
  • Abscess
  • Strictures (obstructions)
  • Perianal fissures
Cancer risk
Endoscopy and imaging
  • Typical location: terminal ileum and colon with rectal sparing
  • May affect the entire GI tract
Pattern of inflammation
  • Continuous
Typical diagnostic findings
  • Noncurative surgery may become necessary to alleviate symptoms

The crone and the fat granny skipped over the wrecked cobblestones: the most important features of Crohn disease are creeping fat, granuloma, skip lesions, rectal sparing, and cobblestone sign.

Other differential diagnoses

The differential diagnoses listed here are not exhaustive.

Approach [14]

  • Therapy of CD is based on the following steps:
    1. Treating acute disease
    2. Inducing clinical remission
    3. Maintaining response/remission
  • Patients should be stratified according to their specific prognostic risk factors.
  • For optimal results, therapy should be as individually tailored as possible.
  • Disease activity should be monitored regularly based on objective markers.
  • Patients should be motivated to engage in lifestyle modifications (see below).


Treatment of Crohn disease can be approached in two different ways: step-up therapy and top-down therapy.

Overview of pharmacotherapy for Crohn disease [14][20]


Substance class


Symptomatic treatment
  • Topical 5‑aminosalicylic acid derivatives (5-ASAs) (e.g., suppository, foam, enema)
Acute episode

Mild-to-moderate disease

Moderate-to-severe disease

Severe/fulminant disease
Steroid-refractory disease
Maintenance therapy

Corticosteroids should not be used for long-term maintenance therapy!



  • Minimally-invasive resection of affected and nonfunctional intestinal loops while preserving as much intestinal length and function as possible
  • Indicated when medical therapy fails or patient develops severe complications (e.g., obstruction, stricture, abscess)


  • Balloon dilatation: to treat intestinal stenosis
  • Percutaneous drainage: prevents retention of secretions and abscessation
  • Surgical drainage: when application of percutaneous drainage fails
  • Strictureplasty
    • A surgical procedure that opens up a bowel stricture without having to resect the bowel (bowel-sparing technique)
    • Indicated after multiple resections
  • Limited resection (e.g., proctocolectomy): in case of obstructions or strictures

Crohn disease is mainly treated with medication, but surgical interventions may be required to treat complications or if medical therapy fails.

Surgical intervention alone cannot cure Crohn disease and should therefore be considered as a last resort to avoid complications in which significant amounts of bowel are lost (e.g., short bowel syndrome)!

Additional considerations

Lifestyle modifications

  • Smoking cessation
  • Avoiding certain drugs (e.g., NSAIDs )
  • Minimizing stress

Management of complications and comorbidities

Prevention of malignancies

Intestinal complications

Intestinal fistulas and abscesses [23]

Systemic complications

We list the most important complications. The selection is not exhaustive.

  • CD is a chronic disease that is currently not curable.
  • Life expectancy is normal with proper treatment. [25]
  • 70–90% of all patients will require surgery at some point during their lifetime. [26]
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