Progress in the diagnosis and treatment of inflammatory bowel disease.

Crohn's disease (CD) and ulcerative colitis (UC), the 2 main types of inflammatory bowel disease (IBD), are chronic conditions characterized by active symptom flares alternating with symptom-free periods. Triggered by an underlying idiopathic inflammatory response, the symptoms of CD and UC can include diarrhea, abdominal pain, rectal bleeding, and malnutrition. Between 1 and 2 million Americans are estimated to have CD or UC. In a population-based study from Olmsted County, Minnesota, the incidence and prevalence of UC were 8.8 cases per 100,000 people per year (95% confidence interval [CI]: 7.2–10.5) and 214 cases per 100,000 people (95% CI: 188–240), respectively. The incidence and prevalence of CD were 7.9 cases per 100,000 people per year (95% CI: 6.3–9.5) and 174 cases per 100,000 people (95% CI: 151–197), respectively.1 Both UC and CD are diagnosed more frequently in individuals between the ages of 15 and 40 years, with the peak incidence occurring during the third decade of life, but children and elderly individuals are also occasionally diagnosed with IBD. While the causes of IBD remain unclear, the underlying pathophysiology of the disease can be traced to inflammation of the mucosal lining of the intestinal tract, which leads to ulceration, edema, bleeding, and loss of fluids and electrolytes. Researchers do not yet know exactly what triggers IBD, but many patients may have a genetic component to their disease. NOD2/CARD15 is an example of 1 genetic linkage that has been associated with a predisposition for CD.2 IBD is also more common among individuals with a family history of the disease; the age-adjusted risk of IBD is approximately 5% for siblings and 10% for offspring, and children of parents with IBD have a 2- to 30-fold increased risk of developing IBD themselves. 3,4 There is also a much higher concordance of IBD among identical versus fraternal twins.3 Among patients with UC, the most common presenting symptom is diarrhea with occult or frank blood loss; UC patients generally do not experience abdominal pain. CD patients also typically present with diarrhea, but often without bleeding, and CD patients more frequently experience abdominal pain, especially if they have an intestinal obstruction. Classically, this pain is localized to the lower abdomen or lower right quadrant, although it may present anywhere. Painful intestinal strictures and obstructions are inflamed and generally require endoscopic or surgical intervention. While strictures are relatively common in CD, colonic strictures are of significant concern in UC because of their malignant potential. While patients with UC generally do not develop fistulae or perianal disease, they may rarely experience perianal abscesses. In UC, intestinal inflammation is typically restricted to the colon, but CD can affect any portion of the gastrointestinal tract, although the ileum and the colon are the most commonly affected sites. Identifying the area of disease involvement is important, as it largely dictates the types of manifestations that IBD patients experience. In addition to slightly different presentations, CD can often be distinguished from UC on endoscopy, as the 2 conditions show differences in pathology. While the inflammation associated with UC is typically continuous and superficial, affecting only the intestinal mucosa and submucosa, the inflammation associated with CD often exhibits a discontinuous pattern that is transmural.