Crohn Disease Diagnosis
Mercedes Mathena
Stool tests. A stool test is the analysis of a sample of stool. Your doctor will give you a container for catching and storing the stool. You will receive instructions on where to send or take the kit for analysis. Doctors use stool tests to rule out other causes of digestive diseases.
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Crohn's disease is a chronic inflammatory condition that affects the gastrointestinal tract. It can cause lesions from mouth to anus and may result in extraintestinal complications. The prevalence of Crohn's disease is increasing in adults and children. Genetic predispositions to Crohn's disease have been identified, and specific environmental factors have been associated with its development. Common presenting symptoms include diarrhea, abdominal pain, rectal bleeding, fever, weight loss, and fatigue. Physical examination should identify unstable patients requiring immediate care, include an anorectal examination, and look for extraintestinal complications. Initial laboratory evaluation identifies inflammation and screens for alternative diagnoses. Measurement of fecal calprotectin has value to rule out disease in adults and children. Endoscopy and cross-sectional imaging are used to confirm the diagnosis and determine the extent of disease. Treatment decisions are guided by disease severity and risk of poor outcomes. Patients commonly receive corticosteroids to treat symptom flare-ups. Patients with higher-risk disease are given biologics, with or without immunomodulators, to induce and maintain remission. For children, enteral nutrition is an option for induction therapy. All patients with Crohn's disease should be counseled on smoking avoidance or cessation. Patients with Crohn's disease are at increased risk of cancer, osteoporosis, anemia, nutritional deficiencies, depression, infection, and thrombotic events. Maximizing prevention measures is essential in caring for these patients.
Crohn's disease is a chronic inflammatory condition affecting the gastrointestinal tract that often causes extraintestinal complications. Inflammation may occur at any point from mouth to anus (Table 11 ). Specific clinical and diagnostic characteristics distinguish Crohn's disease from ulcerative colitis1,2 (Table 21 ). In the United States, the prevalence is estimated at 58 per 100,000 children and 119 to 241 per 100,000 adults, and is increasing for both groups.3,4 Most cases are diagnosed in the 20s to 40s, but new cases do occur later.5 White race and higher education levels are associated with increased prevalence.4 The estimated annual economic burden to U.S. health care is $6.3 billion.6
Current data suggest an interplay between genetic susceptibility and environmental factors in the development of Crohn's disease. Genetic loci have been identified that increase risk. For example, homozygosity for the NOD2 gene has shown a 20- to 40-fold increased risk of developing Crohn's disease.5 Environmental factors associated with increased risk include smoking, oral contraceptive use, antibiotic use, regular use of nonsteroidal anti-inflammatory drugs, and urban environment.5,7 Factors associated with decreased risk include exposure to pets and farm animals, bedroom sharing, having more than two siblings, high fiber intake, fruit consumption, and physical activity.5,8 Vaccines have not been associated with the development of Crohn's disease.9
Crohn's disease most often presents insidiously but can present as an acute toxic illness. Common symptoms include diarrhea, abdominal pain, rectal bleeding, fever, weight loss, and fatigue.1,2 A case review of 201 participants compared patients with Crohn's disease and patients without Crohn's disease who had irritable bowel syndrome or were otherwise healthy. The study identified eight red flag findings for Crohn's disease in adults. In order of strength of association, the findings were perianal lesions other than hemorrhoids, a first-degree relative with inflammatory bowel disease, weight loss (5% of usual body weight) in the past three months, abdominal pain for longer than three months, nocturnal diarrhea, fever, no abdominal pain for 30 to 45 minutes after meals, and no rectal urgency.10 A case review of 606 children with chronic abdominal pain identified three red flag findings for children: anemia, hematochezia, and weight loss.11 The history should identify findings specific for Crohn's disease, identify alternative diagnoses (Table 31,2,12 ), and search for extraintestinal findings (Table 41 ). Important areas to cover are nocturnal symptoms; urgency findings; food intolerance; travel; medications (including antibiotic exposure); smoking status; family history of inflammatory bowel disease; and eye, joint, or skin symptoms.
The physical examination should first identify unstable patients that need immediate attention. Pulse, blood pressure, temperature, respiratory rate, and body weight should be measured. Abdominal examination findings can include tenderness, distention, and/or masses.1,2 An anorectal examination is required, and a pelvic examination should be considered because abscesses, fissures, or fistulas are common in Crohn's disease.1,2 Perianal findings (e.g., fistulas, abscesses) increase the likelihood of Crohn's disease.10
The inflammatory effects of Crohn's disease can extend beyond the intestinal lumen, causing abscesses, fissures, and/or fistulas, and can affect organs outside of the intestinal tract. Patients can present with extraintestinal findings before gastrointestinal symptoms are prominent. Areas affected include, but are not limited to, the eyes, hematologic system, joints, and skin (Table 41 ). History, physical examination, laboratory testing, and imaging are important in identifying these manifestations.1,13
Laboratory testing has multiple purposes for the evaluation of Crohn's disease, including diagnosis, monitoring of disease activity, and tracking adverse effects and effectiveness of medications. Fecal calprotectin is a reasonable test to rule out Crohn's disease for adults (sensitivity of 83% to 100%; specificity of 60% to 100%) and children (sensitivity of 95% to 100%; specificity of 44% to 93%) with equivocal symptoms, and may spare them from more invasive testing.2,14 When the diagnosis of Crohn's disease is considered, a complete blood count; a complete metabolic panel; pregnancy test; C-reactive protein level; erythrocyte sedimentation rate; and stool studies for Clostridium difficile, ova and parasites, and culture may be useful. Results can provide information to support the diagnosis, identify the severity of disease, or determine alternative diagnoses.1,2 Measurement of C-reactive protein, fecal calprotectin, and stool lactoferrin can help assess disease activity and potentially limit the need for endoscopy in disease management decisions.15
Endoscopy and imaging are essential tools for diagnosing and monitoring Crohn's disease. Endoscopic procedures allow direct visualization of and access to the bowel lumen. Direct visualization allows for identification of characteristic lesions, monitoring the success or failure of therapy, and screening for colorectal cancer. Endoscopic procedures (except capsule endoscopy) also allow for biopsy and therapeutic interventions (Table 52,13,18,19 ).
Cross-sectional imaging techniques, including computed tomography (CT), magnetic resonance imaging, and ultrasonography, have come to the forefront in the management of Crohn's disease. These techniques are all useful and provide similar accuracy for making the initial diagnosis, monitoring disease activity, and identifying complications (e.g., fistulas, abscesses).20,21 They complement endoscopy because they can identify extraluminal pathology and examine the gastrointestinal tract not accessible to endoscopic procedures. If the patient can tolerate the contrast load, CT and magnetic resonance enterography are preferred to standard CT and magnetic resonance imaging protocols. CT studies provide the most consistent results but have the downside of radiation exposure. Magnetic resonance studies have no radiation exposure, but are expensive, may have limited availability, and are more difficult for patients to tolerate. Ultrasonography is readily available and has no radiation exposure, but it is highly operator dependent and can be limited by body habitus. Choosing which modality to pursue depends on the patient's age, pregnancy status, current clinical condition, local expertise, and availability13,20,21 (Table 613,21,22 ).
The diagnosis of Crohn's disease results from clinical findings coupled with endoscopic, histologic, radiologic, and/or biochemical testing. History, physical examination, and basic laboratory findings drive the decision to pursue the diagnosis. If the patient has a toxic presentation, standard CT should be the first test. If the patient does not have a fulminant presentation, ileocolonoscopy with biopsy should be the first test, and esophagogastroduodenoscopy should be considered for children. Cross-sectional imaging should follow so that the full extent of disease seen by endoscopy can be determined or to identify disease not visualized by endoscopy. Identifying the complete extent of disease is important for developing a treatment plan. When ileocolonoscopy and cross-sectional imaging are negative and concern for Crohn's disease is still high, capsule endoscopy would be the next step. If this study is negative, it is moderately certain that the disease is not present1,2,13,20,21 (Figure 11,2,13,14,18,19,21 ).
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