Crohn disease !

Crohn disease is a chronic inflammatory bowel disease that can affect any part of the gut in patches; it causes pain, diarrhoea, narrowing and fistulas.

Updated 2026-10-29

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Why it happens

What it is

Chronic, relapsing inflammatory bowel disease that can affect any part of the digestive tract from mouth to anus, with patchy (skip) lesions and transmural inflammation that leads to strictures and fistulas.

Who gets it

Usually starts between the teens and the thirties, with a second smaller peak later in life. Incidence is rising in Latin America, including Colombia, although ulcerative colitis is generally reported more often in the region.

Causes

Abnormal immune response to gut bacteria in genetically susceptible people
Susceptibility genes such as NOD2
Environmental triggers and changes in the gut microbiome

Risk factors

Smoking (raises risk and worsens the course)
Family history of inflammatory bowel disease
Urban, industrialised lifestyle
Frequent antibiotic use (proposed)

Pathophysiology

Inflammation involves the full thickness of the wall (transmural) and appears in skip lesions separated by normal bowel. The terminal ileum and caecum are most often affected. Deep ulcers give a cobblestone mucosa, non-caseating granulomas may form, and wall damage leads to strictures, fistulas and abscesses.

Classification

Montreal: age at diagnosis, location (ileal, colonic, ileocolonic, upper GI) and behaviour (inflammatory, stricturing, penetrating), plus perianal disease
Activity scores (for example CDAI, Harvey-Bradshaw)

Symptoms and signs

Chronic diarrhoea, usually without visible blood
Abdominal pain, often in the right lower quadrant, with a possible mass
Weight loss, fatigue, fever; growth delay in children
Perianal disease: fistulas, abscesses, fissures, skin tags
Mouth ulcers
Extraintestinal: arthritis, sacroiliitis, erythema nodosum, pyoderma gangrenosum, episcleritis, uveitis

Diagnosis

Clinical: Based on history, examination including the perianal area, and combined endoscopic, histological and imaging findings; no single test is diagnostic.
Tests: Full blood count, CRP, albumin, iron, vitamin B12 and folate. Faecal calprotectin. Stool tests to exclude infection, including Clostridioides difficile. Ileocolonoscopy with biopsies (non-caseating granulomas). Tuberculosis is excluded before immunosuppression.
Imaging: MR or CT enterography for small bowel disease, strictures and fistulas; pelvic MRI for perianal fistulas; intestinal ultrasound; capsule endoscopy when strictures are excluded.

Differential diagnosis

Ulcerative colitis
Intestinal tuberculosis (important in Colombia)
Infectious enterocolitis (Yersinia, amoebiasis)
Acute appendicitis
Intestinal lymphoma
Irritable bowel syndrome

Goal of treatment

Induce and keep remission with healing of the mucosa, prevent strictures, fistulas and surgery, and keep growth, nutrition and quality of life normal.

Treatment

Medical: Corticosteroids (including locally acting forms for ileocaecal disease) for short-term induction; not used for maintenance.
Medical: Immunomodulators (thiopurines, methotrexate) for maintenance and with biologics.
Medical: Biologic therapy (anti-TNF, anti-integrin, anti-interleukin 12/23 or 23 agents) for moderate to severe disease; small-molecule (JAK inhibitor) options in some cases.
Procedure: Antibiotics and drainage (seton) for perianal abscesses and fistulas.
Surgical: Surgery for strictures, fistulas or failure of medical treatment: bowel-sparing resection or strictureplasty.
Lifestyle: Stopping smoking; nutritional support, including exclusive enteral nutrition in children.
Follow-up: Monitoring with calprotectin, endoscopy and imaging; vaccination and cancer screening while on immunosuppression.

Drugs for this condition

Complications

Strictures and bowel obstruction
Fistulas (enteroenteric, enterovesical, enterocutaneous, perianal) and abscesses
Malabsorption, vitamin B12 deficiency, anaemia
Gallstones and oxalate kidney stones after ileal disease
Colorectal cancer in long-standing colonic disease
Venous thromboembolism, osteoporosis

Prognosis

A lifelong, relapsing disease. Many patients need surgery at some point and the disease can recur after resection. Early effective therapy and stopping smoking improve the course; life expectancy is close to normal.

Prevention

Not smoking, to lower flares and relapse after surgery
Colonoscopic surveillance in long-standing colonic disease

Test yourself

Think of the answer, then tap the question to see it.

How do the lesions of Crohn disease differ from those of ulcerative colitis?

Crohn has skip lesions anywhere from mouth to anus with transmural inflammation; ulcerative colitis is continuous from the rectum and limited to the mucosa.

Which part of the bowel is most often affected in Crohn disease?

The terminal ileum and caecum (ileocolonic disease).

Which histological finding supports Crohn disease?

Non-caseating granulomas, together with transmural inflammation.

How does smoking affect Crohn disease?

It raises the risk of developing it and worsens the course, with more flares and more recurrence after surgery.

Which infection must be excluded before diagnosing Crohn disease in Colombia?

Intestinal tuberculosis, which also affects the ileocaecal region; it must also be excluded before biologic therapy.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Crohn Disease (StatPearls (NCBI Bookshelf), 2025).

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Representative model, for educational purposes only.

Ileum highlighted on the Durgical 3D model