Epidemiology
- annual incidence in the UK is approximately 5/100,000.
- prevalence is 30-50 per 100,000.
- women more affected than men
- most commonly affected age group is between 15 and 35 years. There is also a second peak in the elderly.
- familial clustering and involves ulcerative colitis as well as Crohn's disease.
- more common in smokers than non-smokers (4:1).
- most common site of disease is the terminal ileum.
Aetiology
The cause of Crohn's disease is unknown. Several factors have been suggested:
- genetic - in up to 20% of patients with Crohn's disease there is another family member affected by Crohn's or ulcerative colitis. There is a weak association with HLA-DR1 and DRQ5 in California, USA
- smoking - increased risk of Crohn's
- infective organism - the following are suggestions, none are proven:
- Mycobacterium paratuberculosis causes a granulomatous inflammation in the small intestine of cattle
- persistence of measles virus; those born at the time of measles epidemics seem to be at higher risk
- diet - low intake of fibre from fruit and vegetables has been associated with the development of Crohn's
- immune mechanisms - may be a down-regulating of the normal mucosal immune response in Crohn's
Pathological features
Macroscopically in Crohn's disease there may be a swollen, reddened and rubbery bowel with:
- skip lesions - discontinuous sites of pathology along the gastrointestinal tract
- cobblestone ulceration; a result of apthous ulceration progressing to oedema and nodular thickening
- lead pipe thickening - thickened, stiff bowel
- narrowed lumen
- strictures
- 'rose-thorn' narrow-mouthed ulcers which lead to fistulae
- fistulae, often between adherent bowel and/or bladder, vagina, other abdominal organs or the abdominal wall
- mesenteric fat covering serosa
- enlarged mesenteric nodes
Microscopically, there is:
- non-caseating granulomas - not always present
- transmural inflammation and lymphocyte infiltration
Crohn's disease may involve any part of the bowel from the mouth to the anus:
- the terminal ileum is involved in nearly 50% of cases
- jejunoileitis is also seen, but most ileal inflammation usually ends abruptly at the ileocaecal junction
- caecal and right colonic involvement is more common than lesions in the stomach and duodenum
Clinical features
This is a chronic, relapsing and remitting disease that has symptomatology dependent on the site of involvement of the GI tract. The commonest site at presentation is the terminal ileum and proximal colon.
Various symptoms occur in most patients:
- abdominal pain
- weight loss
- diarrhoea
Special note must be taken that:
- Crohn's disease may present with an acute onset of abdominal pain that may mimic acute appendicitis or yersinia ileitis.
- common features in active disease are lassitude, anorexia, malaise, and fever.
- in adolescents, a presentation with weight loss alone (without abdominal pain or diarrhoea) may be misdiagnosed as anorexia nervosa.
Differential diagnosis
The differential diagnosis of Crohn's disease includes:
- ulcerative colitis. In 10 to 20% of cases the two diseases cannot be differentiated. Distinguishing features include rectal involvement and bloody diarrhoea in UC, continuous disease pathology, but no strictures or fistulae. In UC there is a low plasma IL-6 in the active disease, and there is a stronger association with non-smokers. Also, UC patients are more often p-ANCA positive.
- irritable bowel syndrome. This has no radiological abnormalities or weight loss.
- gastrointestinal malignancy. The most important cancers here are lymphoma, right colonic cancer and small bowel cancer. These patients might be expected to have night sweats and anaemia. Radiologically there may be a mass and metastases.
- ileal tuberculosis. This should be investigated for with a stool culture, and might be suspected in the immigrant population. Pathologically, after laparoscopic biopsy there will be caseating granulomas and mesenteric tubercules.
- anorexia nervosa
- coeliac disease - this will cause a malabsorptive picture
- chronic infection with Giardia, Yersinia and Campylobacter
- amyloidosis
- Behcet's disease
- Whipple's disease
Investigations
Investigations in Crohn's disease are aimed at:
- making the diagnosis. Investigations to establish the diagnosis of suspected Crohn's disease include:
- sigmoidoscopy and rectal biopsy
- small bowel radiology: indicated if there are symptoms suggestive of small bowel involvement - diarrhoea, pain and weight loss. Crohn's colitis should be excluded by a subsequent barium enema.
- barium enema: this is often more readily available than a colonoscopy. If positive, then small bowel radiology may be indicated to exclude other disease sites.
- bloods:
- anaemia is common - generally iron deficiency anaemia, rarely B12 or folate deficiency
- ESR and platelet count are usually raised, albumin is usually lowered
- stool examination: Cl difficile toxin assay, pathogens
- biopsy: granulomata are characteristic
- colonoscopy: assessment of strictures, colonic polyps, allow biopsy of terminal ileum, or multiple biopsies if a barium enema was equivocal.
- laparotomy: often necessary to distinguish a Crohn's stricture from other causes of strictures, e.g. malignancy. Particularly relevant to the ileal form.
- monitoring disease activity.
- clinical - active disease may present with anorexia, malaise, fever, weight loss and tachycardia.
- blood tests - raised ESR, CRP or platelet count, or a low albumin or anaemia, occur in active disease. However, a normal ESR and CRP do not imply inactive disease.
- radiology - ulcers, fistulae, or disease at a new site on barium studies indicate activity.
- endoscopy - ulcers.
- ultrasound - may reveal thickened bowel loops, an inflammatory mass or abscess.
- Imaging
- plain abdominal radiograph should be carried out - there may be signs of sacro-ileitis and skip lesions, although the latter are hard to see on the plain film.
- small bowel contrast study there may be strictures, fistulae and ulceration - rose thorn ulcers - and cobblestone mucosal surfaces. Kantor's string sign - luminal narrowing of the ileum - may be present, with clinical features of partial obstruction.
- large bowel enema may demonstrate discontinuous skip lesions with normal bowel between, a ragged luminal outline due to ulceration, and loss of haustration. Other features may include rose thorn ulcers and pseudo-diverticulae caused by fibrotic stricturing.
- CT scanning may show an inflammatory mass or an abscess.
- labelled white cell scan may also be helpful in the demonstration of the extent of inflammation if barium radiology is equivocal.
- ultrasound is useful in detection of abscesses.
- radionucleotide scanning may be useful in detection of areas of disease activity.
- MRI is the procedure of choice for the investigation of complex perianal disease.
- in children the bone age may be two or more years less than the chronological age.
- endoscopy: both upper and lower GI endoscopy.
- the disease is not continuous
- the rectum is not always involved (50%)
- fissures are often seen
- skip lesions, cobblestone appearance of mucosa, and strictures are often present
- histology: full thickness inflammation, non-caseating granulomata, fissuring, ulceration, erosions.
Diagnosis
Diagnosis of Crohn's disease is based on clinical, radiological and pathological evidence of the disease.
It involves a careful history of chronic, remitting disease - the problems may take months or years to clinically manifest, barium studies of small and large bowel showing narrowing - Kantor's string sign of the terminal ileum - and skip lesions, stool culture, sigmoidoscopy and rectal biopsy, and colonoscopy with multiple biopsy. Crohn's disease confined to the colon may be difficult to discriminate from ulcerative colitis.
Complications/Associations
The complications of Crohn's disease are best considered as local or general; the general complications include some of the extraintestinal manifestations of Crohn's disease.
Local complications
Possible local complications of Crohn's disease include:
- intestinal obstruction
- haemorrhage
- perforation with abscess
- stricture formation; common
- perianal abscess fistula
- fistulae to the bowel, bladder, vagina
- increased risk of malignancy but less than that of ulcerative colitis.
General complications
Common complications include:
- weight loss
- anaemia
- arthritis - large joints
- erythema nodosum
- ocular problems - conjunctivitis, episcleritis, iritis
- sacroiliitis - this is unrelated to HLA B27
- gall stones, especially of the cholesterol type
Less common:
- liver complications - primary sclerosing cholangitis, fatty liver, non-specific hepatitis, pericholangitis.
- ankylosing spondylitis - related to HLA B27
- pyoderma gangrenosum
- carcinoma of the bile ducts and primary sclerosing cholangitis - much less common than in ulcerative colitis
- renal complications - ureteric stricture, stones, right hydronephrosis, nephropathy (oxalate, amyloid).
- nutritional deficiency - osteomalacia, weakness (potassium, magnesium, vitamin D), lassitude (vitamin B12, folate, iron), rashes (zinc, niacin), alteration of taste (zinc).
- systemic amyloidosis - more common in Crohn's than UC
- reduced fertility
Management
There is no medical or surgical cure for Crohn's disease. If the symptoms are due to inflammation then they generally respond to medical measures. Surgical intervention is usually required when symptoms are due to strictures.
Medical management
- The medical management of Crohn's disease is difficult.
- The general management principles are outlined in management of inflammatory bowel disease.
- aminosalicylates
- corticosteroids - used in acute disease
- steroid-sparing agents
- metronidazole
- cholestyramine
- elemental diet
- anti-TNF-alpha agents
- There is clear evidence that stopping smoking reduces the risk of recurrence
Surgical management
Surgical intervention is limited in Crohn's disease because:
- the whole alimentary tract may be affected from mouth to anus
- the disease is often active at more than one site
- Consequently, there is a high incidence of postoperative complications following surgery, and a concept of minimal surgical intervention has thus been reached.
Indications for surgery in Crohn's disease include:
- persistent ill-health with intractable disease despite medical management
- retardation of physical and sexual development in children
- intestinal obstruction that does not respond to medical therapy
- toxic dilatation of the colon
- perforation, external fistula or abscess formation
- periureteric inflammation causing ureteric obstruction
- suspicion of carcinomatous change
Types pf operations
- ideally resection with primary reanastomosis
- bypass obstruction, e.g. duodenum
- stricturoplasty in patients at risk of developing short bowel syndrome
- extensive colonic involvement may require panproctocolectomy
- There is a 30-50% recurrence rate mostly at the neoterminal ileum; however, patients are still palliated well and not all require reoperation. Surgical procedures should be covered with corticosteroids.
Prognosis
- most patients have a chronic intermittent disease course, while 13% have an unremitting disease course and 10% have a prolonged remission
- less than half require corticosteroids at any point
- during any given year, approximately 10% are treated with corticosteroids and 30% are treated with 5-aminosalicylates
- up to 57% of patients require at least one surgical resection
- about one tenth of patients have prolonged remission
- nearly 75% of patients have a chronic intermittent course, and about one eighth have an unremitting course
- if the patient has both small and large bowel disease then about 70% will require surgical intervention.
- The atypical form of Crohn's is an acute ileitis. This, unlike other forms of Crohn's, does not recur and may represent a completely different disease.
- The excess mortality in patients with Crohn's disease is approximately double that of the general population. This is due to the complications of active disease.
COURTESY:esurgicalhandbook.com
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