- Clinical science
Crohn disease (CD) is an inflammatory bowel disease, the pathogenesis of which is not fully understood. The clinical presentation of CD may be similar to ulcerative colitis (UC), the other most common inflammatory bowel disease. CD mostly affects young adults and adolescents between the ages of 15 and 35. It is typically located in 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. It is often difficult to diagnose because there is no confirmatory test. Diagnosis is therefore 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, and in severe cases, immunosuppressants may be indicated. Antibiotics and surgical intervention may be needed to help treat complications. Because the entire gastrointestinal tract may be affected, Crohn disease cannot be cured (in contrast to ulcerative colitis). The goal of treatment is thus to avoid the progression and recurrence of inflammatory episodes.
- Prevalence: up to 200 cases per 100,000 adults
- Incidence: 3–15 cases/100,000 persons per year
- Sex: ♂ = ♀
Average age at diagnosis: 15–35 years
- A second peak is observed around the age of 60, when 10% of cases occur.
- More common in white populations and people of Jewish descent (especially Ashkenazi Jews, middle European Jews)
Epidemiological data refers to the US, unless otherwise specified.
- Cause: Unknown factors lead to an imbalance between proinflammatory and anti-inflammatory mediators.
- Risk factors
Nicotine consumption is the only (known) controllable risk factor for Crohn disease. Therefore, quitting smoking is especially important for patients with CD!
Crohn Disease Activity Index (CDAI)
The Crohn Disease Activity Index is a validated score that quantifies the severity of an acute episode and evaluates the therapeutic success following recurrence. The CDAI is complex and seldom used in clinical contexts.
The following signs and symptoms are included in the score:
- Number of defecations per day
- Evaluation of abdominal pain
- Evaluation of general condition
- Joint pain
- Aphthous stomatitis
- Body weight
Unknown mechanisms lead to the activation of lymphatic cells (Th1) in the intestinal walls → inflammation is triggered → local tissue damage (edema, erosions/ulcers, necrosis) → obstruction, fibrotic scarring, stricture, and strangulation of the bowel
- Mutations in nucleotide oligomerization binding domain 2 (NOD2) protein implicated in the development of Crohn disease but mechanism currently not fully understood
- Abscess and fistula formation: intestinal aphthous ulcers → transmural fissures and inflammation of the intestinal walls → adherence to other organs or the skin → penetration of these structures → microperforation and abscess formation → macroperforation into these structures → fistula formation
- Main locations: terminal ileum and colon but it can be located anywhere between the mouth and the anus (the rectum is spared)
Typically, CD occurs episodically and there is a 30% risk of recurring inflammation over the span of one year. If symptoms persist for six months, the disease is considered chronic.
- Typically non-bloody, chronic diarrhea
- Abdominal pain, typically in the RLQ
Signs of malabsorption
- Weight loss
- Failure to thrive and growth failure in children
- Complications of disturbed reabsorption of bile acids
- Abdominal mass : the solid mass is often palpable in the RLQ
- Enterocutaneous fistula formation, typically seen in the perianal region
Clinical features of abscesses (∼ 50% of cases) and fistulas (∼ 30% of cases)
- Typically involve the terminal ileum and/or perianal region
- Recurrences are common
- See and
- If intestinal stenosis/strictures: possible signs of bowel obstruction/(sub‑)ileus (vomiting, obstipation)
- If perforation → signs of peritonitis
Perianal fistulas and abscesses are often the first signs of Crohn disease!
- Joints: enteropathic arthritis (e.g., sacroiliitis)
- Eye: iritis, episcleritis, uveitis
- Liver/bile ducts: primary sclerosing cholangitis (PSC; less common than in UC)
- Erythema nodosum
- Acrodermatitis enteropathica
- Associated with various conditions, including Crohn disease, UC, rheumatoid arthritis, and trauma
- Most common site: extensor side of the lower limbs
- Clinical features: very painful, rapidly-progressive, red spots that can change into purulent pustules or deep ulcerated lesions with central necrosis
- Therapy: immunosuppressants (corticosteroids, cyclosporine A)
- Pyostomatitis vegetans (oral aphthae)
- Initially: if a patient has clinical features indicating CD, conduct blood and stool tests
- Confirm with endoscopy and/or radiographic imaging and/or biopsy
- Perform contrast radiological studies and/or ultrasonography to assess extent, severity and complications (i.e., abscesses, fistulas or stenoses)
- Plain abdominal x-rays: bowel distention, pneumoperitoneum
Plain radiography with barium swallow (enteroclysis)
- Indication: to detect fistulas or stenoses
- Water-soluble contrast medium is inserted into the small intestine via a nasopharyngeal tube.
- Multiple x-rays are taken in a chronological sequence to evaluate each section.
- String sign
- Creeping fat
- Ultrasound findings
MR enterography with contrast medium (MRI enteroclysis, Hydro-MRI)
- Indication: identification of the extent and pattern of intestinal inflammation, detection of perianal and pelvic disease, and prediction of activity:
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).
- Procedure: ileocolonoscopy with biopsies at various locations throughout the terminal ileum, colon, and rectum
- Typical findings
|Differential diagnostic considerations: Crohn disease and ulcerative colitis|
|Frequency/type of defecation|| |
|Nutritional status|| || |
|Pain|| || |
|Fistulas|| || |
|Endoscopy and imaging|
|Pattern of involvement|
Other differential diagnoses
- Infectious gastroenteritis
- Non-infectious colitis (ischemic, after radiation therapy, after ingestion of drugs, etc.)
- Malignant intestinal transformations
The differential diagnoses listed here are not exhaustive.
- Nicotine abstinence
- Secondary lactose intolerance (approx. 30% of cases): lactose-free diet
- Malabsorption syndrome: appropriate substitution of vitamins, calories, protein, zinc, calcium
- Bile acid diarrhea: administration of ion-exchange resins to bind bile acids (e.g., cholestyramine)
- During acute episodes: avoid dietary fiber and consider parenteral nutrition
- Treatment of Crohn disease can be approached in two different ways: step‑up therapy and top‑down therapy.
- Step-up therapy involves treatment with weak medication; if the drug regimen is ineffective, treatment with stronger medication is indicated.
- Top-down therapy works the other way around, beginning with stronger medications.
| || |
|Acute episode|| |
For mild to moderate disease
Moderate to severe disease
Steroid-refractory disease, escalation therapy
|Maintenance therapy|| |
- Resect affected and non-functional intestinal loop(s) while preserving intestinal length and function
- Minimally-invasive surgery if possible
- Failed medical therapy
- Severe complications (e.g., abscesses, perforation, toxic megacolon, obstruction, stricture, hemorrhage etc.)
- Resection of affected bowel (e.g., ileostomy, ileocolostomy, colectomy, proctocolectomy)
- Intestinal stenosis: balloon dilatation or tissue-sparing end-to-end anastomosis
- Fistulas, abscesses: percutaneous drainage (prevents retention of secretions and abscessation); if unsuccessful, surgical drainage
- Obstruction, stricture: conservative resection
- After multiple resections: strictureplasty (bowel-sparing technique)
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)!
- Check-ups: Because of the increased risk of colorectal carcinoma and/or recurrence of the disease, regular check-ups that include intestinal endoscopy should be conducted.
- The patient should stop smoking!
- Medical prophylaxis (mesalamine, antibiotics, azathioprine, 6-mercaptopurine, TNF-α antibodies)
- Intestinal complications (see “Clinical findings” above)
- Increased risk of carcinoma
- Growth retardation in children
- Short bowel syndrome and associated issues after surgeries
- In inflammatory conditions: inflammation of the intestinal walls → adherence to other organs or the skin → penetration of these structures → microperforation and possibly abscess formation → macroperforation into these structures → fistula formation
- After surgery or percutaneous drainage: deficient anastomoses and/or sutures, or improper healing following intervention (e.g., due to reduced organ blood flow) → leakage of intestinal fluids → local infection → abscess formation and/or erosion → fistula formation
Clinical features: may vary depending on location of fistula
- Enterocutaneous fistulas: drainage of intestinal content through the skin
- Enteroenteric fistula: mostly asymptomatic
- Ileosigmoid fistula: diarrhea, weight loss; , abdominal pain
- Gastrocolic fistula: abdominal pain; , weight loss, foul‑smelling burps (feculent belching)
- Enterovesical/colovesical fistula: passing urine together with air (pneumaturia), excrements in urine (fecaluria), recurrent urinary tract infections (UTI)
- Rectovaginal/anovaginal fistula: passage of stool/gas through the vagina, pain during sex (dyspareunia), perineal pain
- Aortoenteric fistula: rectal bleeding
We list the most important complications. The selection is not exhaustive.
- Currently not curable
- Relapses and complications are very common without treatment.
- 70% of all patients require surgery within 15 years of the onset of complications.
- Life expectancy is normal with ideal, evidence-based treatment.