Once IBD has been established by ruling out infectious colitides, a standard evaluation includes contrast imaging of the small intestine, esophagogastroduodenoscopy, colonoscopy, ileoscopy, and multiple biopsies of the intestinal tract to differentiate CD from UC. Multiple imaging studies are currently available to visualize the small bowel. Standard barium small-bowel follow-through, computed tomography enterography, magnetic resonance enterography, and capsule enteroscopy all play a role in visualizing the GI tract. Indeed, a 4-way comparison of small-bowel follow-through, CT enterography, ileoscopy, and capsule enteroscopy found no statistical difference between the 4 examinations for detecting active small-bowel CD. Importantly, capsule enteroscopy should be used with caution as a first-line study due to the possibility of undetected small-bowel obstruction resulting in retained capsule. In our practice, CT enterography has been the test of choice to evaluate the small intestine due to its sensitivity and specificity to detect bowel inflammation, proximal intestinal dilation, intraperitoneal inflammatory lesions, and the extent of disease. Recently, MR enterography has become more popular due to concerns of radiation exposure during a computed tomography scan in children. Image quality and diagnostic effectiveness for MR enterography has yet to be determined as compared to CT enterography.
Upper and lower endoscopies with multiple biopsies are the mainstay of establishing the diagnosis of CD versus UC. The transmural, panintestinal inflammation of CD may be detected in up to 30% of patients during esophagogastroduodenoscopy. Visualizing the terminal ileum is extremely important. Backwash ileitis is mucosal inflammation associated with severe UC, whereas the transmural inflammation of CD results in deep linear ulcers referred to as bear claw deformity. Demonstration of nonpericryptal granulomas is a hallmark of CD on histological examination. Endoscopic findings of pseudopolyps are a result of mucosal erosion due to UC.
The classic histologic findings of UC include disruption of crypt architecture, crypt abscess formation, and infiltration of the lamina propria with leukocytes. While determining CD from UC seems straightforward; in fact, 10% to 15% of patients demonstrate findings consistent with both CD and UC. These patients have IC and require repeat evaluation in the future. The North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition and the Crohn's and Colitis Foundation of America have developed recommendations to assist the clinician in differentiating CD from UC (Fig. 49-1).
Diagnostic algorithm to differentiate Crohn disease from ulcerative colitis. (Adapted from J Pediatr Gastroenterol Nutr 44(5):653–674.)
Serum biomarkers have been extensively studied in both adults and children (Table 49-1). They effectively differentiate IBD from noninflammatory conditions. Distinguishing CD from UC is more problematic, but the standard findings of anti-Saccharomyces cervisiae antibodies (ASCA) in CD and elevated titers of perinuclear antineutrophil cytoplasmic antibody (p-ANCA) in UC remain true. Furthermore, a high ASCA titer in a patient with CD indicates a strong possibility of surgery in the near future. Unfortunately, the specificity is low for these serum biomarkers. For example, colon predominant CD is a common pediatric presentation and p-ANCA occurs in these patients. Thus, serum biomarkers are not diagnostic, but may help differentiate CD from UC when the standard evaluation is equivocal.
Table 49-1The Prevalence of Serum Biomarkers in Crohn Disease and Ulcerative Colitis |Favorite Table|Download (.pdf) Table 49-1 The Prevalence of Serum Biomarkers in Crohn Disease and Ulcerative Colitis
|Serum Biomarker ||Prevalence in Crohn Disease ||Prevalence in Ulcerative Colitis |
|ASCA (anti-Saccharomyces cerevisiae antibody) ||60%-70% ||10%-15% |
|p-ANCA (perinuclear antineutrophil cytoplasmic antibody) ||10%-15% ||60%-70% |
|I2 antibody ||55% ||10% |
|OmpC antibody ||55% ||5%-10% |
|CBir1 antibody ||55% ||10% |
|ACCA (anti-chitobioside carbohydrate antibody) ||20%-40% ||<10% |
|ALCA (antilaminaribioside carbohydrate antibody) ||20%-40% ||<10% |
|PAB (antipancreatic antibody) ||20%-40% ||<10% |