How should I diagnose and treat an adult patient presenting with abdominal pain, bloody diarrhea, weight loss, and fatigue suspected of having Crohn’s disease?

Diagnosis and Management of Crohn's Disease

For an adult patient presenting with abdominal pain, bloody diarrhea, weight loss, and fatigue suspected of having Crohn's disease, perform ileocolonoscopy with segmental biopsies from at least five sites including the ileum and rectum, combined with MR enterography as first-line imaging to assess small bowel disease extent. 1

Diagnostic Approach

Initial Endoscopic Evaluation

• Ileocolonoscopy with biopsy is the first-line investigation for suspected Crohn's disease, obtaining at least two biopsy specimens from five sites throughout the examined bowel, including the terminal ileum and rectum. 1

• Intubation of the terminal ileum is critical because ileoscopy with biopsy histology is superior in establishing the diagnosis of mild ileal Crohn's disease, though up to 20% of patients have isolated proximal small bowel disease beyond the reach of complete ileocolonoscopy. 1

• Upper gastrointestinal endoscopy is NOT routinely required unless the patient has upper gastrointestinal symptoms (dysphagia, odynophagia, persistent nausea/vomiting, or epigastric pain). 1

Cross-Sectional Imaging

• MR enterography (MRE) is preferred as first-line imaging for diagnosis and determining disease extent because it avoids ionizing radiation exposure, which is particularly important for young adults who may require repeated imaging over their lifetime. 1

• MRE has 80% sensitivity and 95% specificity for small bowel disease extent and is significantly more sensitive than intestinal ultrasound (96% vs 90%) for detecting active small bowel disease. 1

• CT enterography should be reserved for acute presentations when MRI is unavailable, as patients with Crohn's disease have more than twice the radiation exposure of ulcerative colitis patients, with 15.5% accumulating doses exceeding 75 mSv (increasing cancer mortality risk by 7.3%). 1

• Intestinal ultrasound (IUS) may be used depending on local availability and expertise, though it has lower sensitivity (70%) and specificity (81%) compared to MRE for small bowel disease extent. 1

Advanced Endoscopic Techniques

• Small bowel capsule endoscopy should be performed when small bowel Crohn's disease is suspected despite normal or inconclusive ileocolonoscopy and cross-sectional imaging, with consideration of a patency capsule first to avoid retention. 1

• Capsule endoscopy is diagnostically superior to barium follow-through and similar to CT and MRE, with particular superiority for more proximal and superficial lesions. 1

Laboratory Assessment

• Stool studies must include bacterial culture and Clostridioides difficile toxin assay to exclude infectious causes before diagnosing Crohn's disease. 1

• Fecal calprotectin has high sensitivity and specificity for distinguishing inflammatory bowel disease from irritable bowel syndrome and should be obtained. 2

• Baseline inflammatory markers (CRP, albumin) should be measured, as low serum albumin indicates more severe disease. 1

Clinical Presentation Recognition

Cardinal Symptoms

• Abdominal pain is present in most patients, typically colicky in nature, often in the right lower quadrant when the terminal ileum is involved. 2, 3

• Diarrhea may be bloody or non-bloody depending on disease location, with small bowel disease more likely to cause non-bloody diarrhea and colonic disease causing bloody diarrhea. 2, 3, 4

• Weight loss and fatigue are common systemic manifestations that distinguish Crohn's disease from ulcerative colitis, which has fewer systemic symptoms. 2, 3, 4

Disease Distribution

• The terminal ileum and colon are most commonly affected, with small bowel alone affected in approximately one-third of patients. 2, 3

• Perianal disease occurs in up to one-third of patients, including fistulas, abscesses, and skin tags, and requires specific assessment with pelvic MRI and examination under anesthesia by an experienced colorectal surgeon. 1, 3

Important Differential Diagnoses

• Intestinal tuberculosis must be excluded in endemic areas, with features suggesting TB including night sweats, concomitant pulmonary TB, and abdominal lymphadenopathy. 2

• Cytomegalovirus testing should be considered in patients with moderate to severe colitis, particularly those with steroid-refractory disease. 2

Treatment Strategy

Mild Disease Management

• For ambulatory outpatients with low-risk, mild ileal or ileocolonic Crohn's disease, budesonide is recommended for induction of remission. 5

• For mild colonic Crohn's disease, sulfasalazine is a reasonable choice, although other aminosalicylates have no role in the treatment of Crohn's disease. 5

• Select patients with mild-to-moderate disease may benefit from maintenance therapy with azathioprine or vedolizumab. 5

Moderate to Severe Disease

• Early "top-down" biologic therapy is recommended in moderate-to-severe Crohn's disease to induce remission and prevent hospitalization and complications. 5, 4

• Infliximab is recommended as first-line advanced therapy for perianal Crohn's disease, with other advanced therapies offered for inadequate response. 1

• Medical therapies should be started promptly after adequate surgical drainage of perianal abscesses. 1

Perianal Disease Management

• Setons should be placed to prevent sepsis in fistulizing perianal Crohn's disease, though optimal timing of seton removal is uncertain and requires shared decision-making. 1

• Patients with perianal Crohn's disease should be managed via the IBD multidisciplinary team including gastroenterology and colorectal surgery. 1

• Patients with severe perianal disease refractory to medical therapy affecting quality of life should be offered fecal stream diversion surgery. 1

Monitoring and Follow-Up

Multimodal Monitoring Approach

• A multimodal approach to monitoring remission is advised, including clinical assessment, biochemical markers (CRP, albumin), fecal calprotectin, imaging (MRE or IUS), and endoscopic evaluation with histology. 1

• Fecal calprotectin should be used to monitor disease in patients with Crohn's disease in a known location where there is a baseline fecal calprotectin. 1

• The specific combination of modalities and frequency depends on disease phenotype, therapy, and duration of remission. 1

Post-Surgical Monitoring

• Assessment of Crohn's disease activity should be performed 6 months after surgery, preferably with ileocolonoscopy using the Rutgeerts score to evaluate postoperative recurrence at the ileocolic anastomosis. 1

Treatment Withdrawal Considerations

• Withdrawal of purine analogues or anti-TNF therapy is associated with significant risk of relapse, whether used as monotherapy or combination therapy, requiring shared decision-making before withdrawal. 1

Critical Pitfalls to Avoid

• Never assume ileocolonoscopy alone is sufficient for diagnosis, as up to 20% of patients have isolated proximal small bowel disease requiring cross-sectional imaging. 1

• Do not use CT enterography routinely when MRE is available, as cumulative radiation exposure significantly increases cancer risk in young patients requiring lifelong monitoring. 1

• Do not perform capsule endoscopy without considering a patency capsule first, as retention rates are higher in established versus suspected Crohn's disease. 1

• Never diagnose Crohn's disease without excluding infectious causes, particularly C. difficile and tuberculosis in endemic areas. 1, 2

• Do not neglect perianal examination and assessment, as perianal disease occurs in one-third of patients and requires specific multidisciplinary management. 1, 3