Crohn's disease is a form of inflammatory bowel disease. It commonly affects the terminal ileum and colon but may be seen anywhere from the mouth to anus.

Pathology

• cause is unknown but there is a strong genetic susceptibility
• inflammation occurs in all layers, down to the serosa. This is why patients with Crohn's are prone to strictures, fistulas and adhesions

Crohn's disease typically presents in late adolescence or early adulthood. Features include:

• presentation may be non-specific symptoms such as weight loss and lethargy
• diarrhoea: the most prominent symptom in adults. Crohn's colitis may cause bloody diarrhoea
• abdominal pain: the most prominent symptom in children
• perianal disease: e.g. Skin tags or ulcers
• extra-intestinal features are more common in patients with colitis or perianal disease

Crohn's disease is a form of inflammatory bowel disease. It commonly affects the terminal ileum and colon but may be seen anywhere from the mouth to anus

Bloods

• C-reactive protein correlates well with disease activity

Endoscopy

• colonoscopy is the investigation of choice
• features suggest of Crohn's include deep ulcers, skip lesions

Histology

• inflammation in all layers from mucosa to serosa
• goblet cells
• granulomas

Small bowel enema

• high sensitivity and specificity for examination of the terminal ileum
• strictures: 'Kantor's string sign'
• proximal bowel dilation
• 'rose thorn' ulcers
• fistulae

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The two main types of inflammatory bowel disease are Crohn's disease and ulcerative colitis. They have many similarities in terms of presenting symptoms, investigation findings and management options.


There are however some key differences which are highlighted in table below:


*impaired bile acid rebsorption increases the loss calcium in the bile. Calcium normally binds oxalate.

Crohn's disease is a form of inflammatory bowel disease. It commonly affects the terminal ileum and colon but may be seen anywhere from the mouth to anus. NICE published guidelines on the management of Crohn's disease in 2012.

General points

• patients should be strongly advised to stop smoking
• some studies suggest an increased risk of relapse secondary to NSAIDs and the combined oral contraceptive pill but the evidence is patchy

Inducing remission

• glucocorticoids (oral, topical or intravenous) are generally used to induce remission. Budesonide is an alternative in a subgroup of patients
• enteral feeding with an elemental diet may be used in addition to or instead of other measures to induce remission, particularly if there is concern regarding the side-effects of steroids (for example in young children)
• 5-ASA drugs (e.g. mesalazine) are used second-line to glucocorticoids but are not as effective
• azathioprine or mercaptopurine* may be used as an add-on medication to induce remission but is not used as monotherapy. Methotrexate is an alternative to azathioprine
• infliximab is useful in refractory disease and fistulating Crohn's. Patients typically continue on azathioprine or methotrexate
• metronidazole is often used for isolated peri-anal disease

Maintaining remission

• as above, stopping smoking is a priority (remember: smoking makes Crohn's worse, but may help ulcerative colitis)
• azathioprine or mercaptopurine is used first-line to maintain remission
• methotrexate is used second-line
• 5-ASA drugs (e.g. mesalazine) should be considered if a patient has had previous surgery

Surgery

• around 80% of patients with Crohn's disease will eventually have surgery
• see below for further detail

Surgical interventions in Crohn's disease

The commonest disease pattern in Crohn's is stricturing terminal ileal disease and this often culminates in an ileocaecal resection. Other procedures performed include segmental small bowel resections and stricturoplasty. Colonic involvement in patients with Crohn's is not common and, where found, distribution is often segmental. However, despite this distribution segmental resections of the colon in patients with Crohn's disease are generally not advocated because the recurrence rate in the remaining colon is extremely high, as a result, the standard options of colonic surgery in Crohn's patients are generally; sub total colectomy, panproctocolectomy and staged sub total colectomy and proctectomy. Restorative procedures such as ileoanal pouch have no role in therapy.

Crohn's disease is notorious for the developmental of intestinal fistulae; these may form between the rectum and skin (perianal) or the small bowel and skin. Fistulation between loops of bowel may also occur and result in bacterial overgrowth and malabsorption. Management of enterocutaneous fistulae involves controlling sepsis, optimising nutrition, imaging the disease and planning definitive surgical management.

*assess thiopurine methyltransferase (TPMT) activity before offering azathioprine or mercaptopurine

As well as the well-documented complications described above, patients are also at risk of:

• small bowel cancer (standard incidence ratio = 40)
• colorectal cancer (standard incidence ration = 2, i.e. less than the risk associated with ulcerative colitis)
• osteoporosis