Diagnostics

Endoscopy, cross-sectional imaging, and laboratory studies are required for the initial evaluation of suspected CD, evaluation of an acute flare, and monitoring response to therapy.

Approach

• Conduct a thorough history and physical examination (including digital rectal examination).

  • Document any extraintestinal manifestations of CD.

  • Evaluate for the presence of perianal fistulas.

• Perform endoscopy and obtain intestinal biopsies.

• Obtain cross-sectional imaging to:

  • Establish location(s) and severity of disease

  • Identify complications (e.g., abscesses, fistulas, strictures)

• Obtain laboratory studies (blood and stool) to:

  • Rule out differential diagnoses of Crohn disease (e.g., infectious gastroenteritis)

  • Assess and monitor disease activity

Small bowel evaluation is an essential part of the initial diagnostic workup of CD. Almost one-third of patients with CD have only small bowel disease and this may not be visible on ileocolonoscopy.

Ileocolonoscopy

• Indication: all patients with suspected CD

  • Assesses the distribution and severity of the disease

  • Aids differentiation of CD from other diseases (e.g., ulcerative colitis)

  • Monitors disease activity (e.g., active disease, remission)

  • Can be used therapeutically (e.g., stricture dilatation)

• Supportive findings

  • Skip lesions: segmental and/or discontinuous pattern of involvement (interspersed with normal tissue)

  • Linear and/or serpiginous ulcerations

  • Small aphthous ulcerations

  • Cobblestone sign: inflamed edematous sections interspersed with deep ulcerations that resemble cobblestones

  • Erythema, fissures, strictures, and fistulas

Discontinuous areas of inflammation, cobblestone appearance of the affected mucosa, and mucosal ulcerations are hallmark endoscopic findings of CD.

Characteristic endoscopic features and evidence of chronic intestinal inflammation on histology are the most important factors to establish a diagnosis of CD.

Cross-sectional imaging is preferred as it permits evaluation of the entire gastrointestinal tract (including the small bowel), can identify complications (e.g., bowel obstruction, abscess, fistula), and can assess for differential diagnoses of CD. [16]

Indications

• Suspected CD (part of initial evaluation)

• Localization of inflammation and assessment of severity

• Evaluation of suspected acute flare or complications (e.g., abscess)

• Serial imaging to assess response to therapy

Modalities and supportive findings

• Cross-sectional enterography (MRE, CTE): preferred imaging modality for CD [11][16][20]

  • Edematous thickening of the intestinal wall

  • Mucosal enhancement, mesenteric fat stranding

  • Creeping fat: excessive mesenteric fat around the affected segments of bowel [22]

  • Can also identify:

    • Complications (e.g., strictures, fistulas, abscesses)

    • Extraluminal disease (e.g., cholelithiasis, urolithiasis)

    • Response to therapy (e.g., healing of ulcers)

• Small bowel follow-through : can identify luminal complications such as internal fistulas and narrowed segment(s) of bowel (string sign) [16]

• Additional modalities

  • Ultrasound abdomen

    • Consider for initial evaluation of suspected CD and for disease monitoring.

    • Supportive finding (of active disease): bowel wall thickening (> 4 mm)

  • Plain x-ray abdomen: Consider for expedited assessment of complications

• To rule out differential diagnoses of CD

  • Stool analysis: to identify ova, cysts, or C. difficile infection in symptomatic patients

  • Serology: not routinely recommended due to low sensitivity [23]

    • ↑ Anti-Saccharomyces cerevisiae antibodies (ASCA): more commonly elevated in CD than in UC

    • pANCA: more commonly elevated in UC than in CD

• To monitor disease activity

  • Fecal calprotectin and/or fecal lactoferrin: proteins associated with neutrophil activation [21]

    • Used as noninvasive markers of intestinal inflammation to monitor disease activity and response to therapy

    • Also used to differentiate IBD from irritable bowel syndrome

  • Inflammatory markers: CRP, ESR, platelets

    • CRP correlates with disease activity better than ESR; both may be normal in patients with mild CD. [11][24]

    • ↑ Thrombocytes may be an indicator of active disease (reactive thrombocytosis) [11][25]

• To identify complications

  • CMP: to identify malnutrition (↓ total protein), end-organ damage (↑ creatinine), and/or dehydration

  • CBC, iron studies, vitamin B12, folate: to evaluate for anemia and micronutrient deficiency [24]

Anemia in CD may result from chronic disease, iron deficiency, and/or vitamin B12 deficiency.