Inflammatory bowel disease (IBD) is an autoimmune disorder that manifests as a chronic, intractable activation of the intestinal immune system. There are two types of IBD – Crohn’s disease and ulcerative colitis. These subtypes are differentiated based on disease location and microscopic findings on biopsy, although considerable overlap exists between the two subtypes. Typically, Crohn’s affects the small intestine while ulcerative colitis affects the large intestine. The peak incidence of Crohn’s disease is among patients aged 15 to 25 years, but all ages are affected. In North America, Crohn’s prevalence is between 6.3 and 23.8 per 100,000 person-years, and the incidence is increasing globally, notably among countries with increasing industrialization, air pollution, and Westernization of their diets. Examples include Brazil, which had an annual incidence increase of 11.1% from 1988 to 2012, and Taiwan, with an annual increase of 4% from 1998 to 2008.
There are multiple contributing factors including genetics, the host microbiome (types of intestinal bacteria), and environmental factors such as smoking, medications, and diet. To date more than 100 genetic markers have been identified for Crohn’s disease. Implicated genes suggest that immunoreactivity to gut bacteria is a critical component in the risk of developing Crohn’s. Interactions between genes and environment may facilitate the development of Crohn’s via damage to the intestinal lining or disruption of immune defenses, both of which may increase the exposure of the primed immune system to intestinal bacteria. Smoking is a proven risk factor for development of Crohn’s, disease flares, and the need for surgery.
Often, symptoms are present for years before the diagnosis is confirmed. Cardinal symptoms of Crohn’s include fatigue, fever, abdominal pain, diarrhea, and weight loss. Rectal bleeding is less common in Crohn’s, unless the distal large intestine is involved, which is rare in Crohn’s but common in ulcerative colitis. Symptoms can fluctuate over time and can be mistaken for irritable bowel syndrome (IBS). About 20% of patients present with complications of Crohn’s, including intestinal strictures (severe narrowing of the lumen [inside] of the bowel), abscesses, or fistulas (abnormal connections between organs, including the skin). Many Crohn’s patients have signs of anemia, iron deficiency, low Vitamin D levels, and elevated markers of inflammation, including C-reactive protein, erythrocyte sedimentation rate (ESR), and fecal calprotectin. Fecal calprotectin is the most sensitive screening test for Crohn’s disease. Manifestations of Crohn’s outside of the intestines are common and include arthritis, sacroiliitis, rashes, eye inflammations, and mouth ulcers.
Medical therapy for Crohn’s disease, like the treatment of all autoimmune disorders, is based on suppressing an overly active immune system. There are two stages of treatment – induction and maintenance. The mainstay of the induction phase is steroids to achieve symptom control. Once disease suppression has occurred (usually after a few months), maintenance therapy is given and is usually lifelong. Maintenance avoids steroids and until recently relied on immune system modulators like azathioprine, 6-mercaptopurine, and methotrexate, however these therapies can have long term side effects such as causing secondary cancers such as leukemia decades later. Thankfully, research has opened up new, less harmful therapies including biological agents and antibodies. In all cases, the patient must be tested for latent diseases that may activate once the immune system is suppressed, for example tuberculosis and hepatitis B. Also, since Crohn’s increases the risk of intestinal cancers, close lifelong screening is important.
By Peter Galvin, MD
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