Crohn disease (CD) and ulcerative colitis (UC) are two conditions commonly referred to inflammatory bowel disease (IBD). They are immunologically mediated inflammatory diseases of the gastrointestinal tract. In CD, the inflammation extends through the entire thickness of the bowel wall from the mucosa to the serosa. The disease runs a relapsing and remitting course. With multiple relapses, CD can progress from an initially mild to moderate inflammatory conditions to severe penetrating (fistulization) and/or stricturing disease.
Although the exact etiology of inflammatory bowel disease (IBD) is not known, there is substantial evidence to suggest that the disease is resulting from an inappropriate immune response in the bowel to situations from environmental factors such as drugs, toxins, infections or intestinal microbes in a genetically susceptible host. More than a hundred genes associated with IBD have been identified. In Crohn's disease particularly, there appears to be a genetic association with phenotypes. Specifically, NOD2/CARD15 mutations were found to be associated with a phenotype of Crohn's disease which was associated in those diagnosed at a younger age, with ileal involvement, increased severity of ileal disease requiring surgical intervention/reoperation. In the future, this genotyping could potentially provide prognostic information on the severity of the disease. Furthermore, it could predict which patient's should be considered for surgical management vs. medical management based on a more detailed understanding of genetic analysis.
Crohn's disease (CD) is most commonly seen in the western developed world in North America, northern Europe, and New Zealand. Its incidence has a bimodal distribution with the onset occurring most frequently between ages 15 to 30 years and 40 to 60 years old. It is more prominent in urban than rural areas. There is a high incidence in Northern Europeans and Jewish descent (incidence 3.2/1000) contrasting to a significant infrequent prevalence in Asians, Africans, and South Americans. However, recent studies have shown a significant increase in incidence in rapidly industrializing areas of Asia, Africa, and Australasia.
The pathophysiology is multifactorial and involves genetic predisposition, infectious, immunological, environmental, and dietary. The characteristic transmural inflammation can include the entire GI tract from mouth to the perianal area; although most frequently involve terminal ileum and right colon. The initial lesion starts out as an infiltrate around an intestinal crypt. This goes on to develop an ulceration first in the superficial mucosa and involves to deeper layers. As the inflammation progresses, non-caseating granulomas form involving all layers of the intestinal wall. It can develop into the classic cobblestone mucosal appearances and skip lesions along the length of the intestine sparing areas with normal mucosa. As the flare of Crohn's settles, scarring replaces the inflamed areas of the intestines.
The immune-mediated response in Crohn's disease involves both innate and acquired mechanisms by macrophages, neutrophils, and T-cells in the intestine which promote pro-inflammatory mediators like TNF-alpha. Colonic Crohn's lesions were found to have high levels of cytokines like IFN-gamma, IL-2, IL-12, and IL-18. Crohn's disease is primarily regulated by TH1 and TH17 mediated processes.
Patients with flare-ups of Crohn's disease typically presents with abdominal pain (right lower quadrant), flatulence/bloating, diarrhea (can include mucous and blood), fever, weight loss, anemia.
In severe cases, perianal abscess, perianal Crohn's disease, and cutaneous fistulas can be seen.
Crohn's disease is associated with extraintestinal manifestations including episcleritis, uveitis, stomatitis, aphthous ulcers, liver steatosis, gallstones, cholangitis, primary sclerosing cholangitis, nephrolithiasis, hydronephrosis, urinary tract infections, arthritis (spine - sacral, knee, ankles, hips, wrist, elbows), ankylosing spondylitis, erythema nodosum, and pyoderma gangrenosum.
Stool tests to rule out infections include culture and sensitivities, ovum and parasites, Clostridium difficile toxins, leukocyte count. Stool for calprotectin can detect active CD and also used for monitoring disease.
Blood tests including baseline CBC and a metabolic panel can highlight the presence of anemia (B12 or iron deficiency) or liver disease. Special serology such as normal anti-neutrophil cytoplasmic antibodies (ANCA) and raised anti-saccharomyces cerevisiae antibodies (ASCA) can distinguish Crohn's disease from ulcerative colitis. C-reactive protein (CRP) or sedimentary rate (ESR) can reflect the severity of the inflammation.
CT scan/MRE of the abdomen and pelvis can detect abscesses and fistulization. The choice between CT or MR enterography is largely directed at minimizing radiation exposure in younger populations. Both give a higher definition of the diseased intestine. However, MRI can provide more detail when investigating the fistulizing disease. The use of video capsule endoscopy (VCE) can visualize the small bowel for CD when regular endoscopy or colonoscopy cannot reach to visualize these areas.
Before initiation of any treatment, vaccination history (tetanus, diphtheria, pertussis, HPV, influenza, pneumococcal, hepatitis A, hepatitis B, MMR, VZV) should be known, if no prior history titers of MMR, VZV, and hepatitis A/B should be checked. Baseline PPD with CXR should also be checked before any treatment. Baseline thiopurine methyltransferase (TPMT) levels should be checked before deciding on treatment options. Low levels of TMPT may result in increased risk of side effects, whereas very high levels may decrease the effectiveness of prescribed treatment.
The medical treatment is broadly grouped into two classes:
Biologics are immunoglobulins engineered to direct against specific cytokines or receptors involving in the inflammation process. Each biologic agent works against one specific site at a molecular level. Anti-tumor necrosis factor (TNF) alpha is a monoclonal antibody that can block the TNF in the circulation from their inflammatory actions. Anti-integrin agents are adhesion molecule inhibitors that bind the subunits of the MAdCAM receptors of the endothelial cells at the inflammatory sites. They halt the trafficking of lymphocytes from the circulation into the wall of the intestine, thereby stopping the inflammatory response targeted at the bowel. Examples of anti-TNF agents are infliximab, adalimumab, golimumab. Examples of adhesion molecule inhibitors are natalizumab, vedolizumab. Vedolizumab is gut-specific and has less systemic side effects. Many newer therapeutic agents for inflammatory bowel disease are in the pipeline.
Surgical treatments are used for complications such as bowel obstructions, abscess, fistulas, or perforated bowel.
The diagnosis and management of Crohn disease is multidisciplinary that includes a nurse practitioner, internists, hematologist, gastroenterologist, general surgeon, dietitian, stoma nurse and a pharmacist. The disorder affects many organs in the body and hence the appropriate specialist should be consulted early on in the disease course. The disorder is usually managed with medications but complications require surgery. Most patients have relapses and remissions and need life long follow up. The prognosis for most patients with crohn disease is guarded and the quality of life is poor. (Level V)
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