What is capsule endoscopy and what are its indications, particularly in adults with suspected small bowel disorders?

Capsule Endoscopy: Description and Clinical Indications

What is Capsule Endoscopy?

Capsule endoscopy (CE) is a noninvasive diagnostic procedure in which a patient swallows a miniaturized camera embedded in a pill-sized capsule that captures images of the small intestine as it travels through the gastrointestinal tract via peristalsis, typically reaching the right colon within 5-8 hours. 1, 2 The images are recorded on a portable hard drive worn by the patient during the examination. 2

Primary Clinical Indications

Obscure Gastrointestinal Bleeding (Strongest Indication)

In patients with overt gastrointestinal bleeding and negative findings on both esophagogastroduodenoscopy (EGD) and colonoscopy, CE should be performed as soon as possible, ideally within 48 hours of the bleeding episode, to maximize diagnostic and therapeutic yield. 1, 3

• CE is the first-line examination for suspected small-bowel bleeding given its excellent safety profile, patient tolerability, and ability to visualize the entire small-bowel mucosa. 3
• Diagnostic yield for GI bleeding reaches 49.3%, with arteriovenous malformations being the most common finding (43.9%), followed by ulcers (24.1%). 4
• CE is also recommended as the first-line examination in patients with iron-deficiency anemia when small bowel evaluation is indicated. 3
• Only selected patients with unexplained, mild, chronic iron-deficiency anemia should undergo CE. 1

Suspected or Known Crohn's Disease

CE should be performed in patients with suspected, known, or relapsed Crohn's disease when ileocolonoscopy and imaging studies are negative, if it is imperative to know whether active Crohn's disease is present in the small bowel. 1

• CE has greater sensitivity for mucosal small-bowel Crohn's disease than radiological imaging techniques, particularly for proximal or superficial small bowel lesions. 1, 5
• CE should be used as the initial diagnostic modality for investigating the small bowel in the absence of obstructive symptoms or known bowel stenosis. 3
• Critical caveat: CE should be restricted to patients with high clinical suspicion (suggestive clinical picture and raised fecal calprotectin) who have abstained from NSAID ingestion for at least 1 month, as minor mucosal abnormalities can be seen in normal individuals, particularly NSAID users. 1, 5
• CE is NOT recommended in patients with chronic abdominal pain or diarrhea without evidence of abnormal biomarkers typically associated with Crohn's disease. 1

Celiac Disease (Limited Role)

CE is recommended to assess patients with celiac disease who have unexplained symptoms despite appropriate treatment, but NOT to make the initial diagnosis. 1

• Duodenal biopsy via gastroscopy remains the gold standard for diagnosing celiac disease. 1
• CE may help demonstrate villous atrophy in patients unable or unwilling to undergo gastroscopy when positive celiac serology is present. 1

Polyposis Syndromes and Small-Bowel Tumors

CE is suggested for surveillance in patients with polyposis syndromes or other small-bowel cancers who require small-bowel studies. 1

• CE has become the gold standard for surveillance of polyposis syndromes. 2

Important Safety Considerations and Contraindications

Capsule Retention Risk

The most significant complication of CE is capsule retention, which occurs when the capsule becomes lodged in the small bowel, usually at stricturing disease sites. 1

• Risk of retention in suspected Crohn's disease: 3.6% (95% CI 1.7% to 8.6%). 1
• Risk of retention in established Crohn's disease: 8.2% (95% CI 6% to 11%). 1
• When obstructive symptoms are present (abdominal pain, distention, nausea, vomiting) or in known stricturing Crohn's disease, a patency capsule should precede CE. 1, 6
• Patients with history of small bowel resection, abdominal/pelvic radiation exposure, or chronic NSAID use should also have patency capsule assessment. 1
• After successful patency capsule passage or exclusion of strictures by cross-sectional imaging, retention risk drops to 2.7% (95% CI 1.1 to 6.4). 1

When NOT to Use CE

Colon capsule endoscopy should NOT be substituted routinely for colonoscopy. 1

• Colon CE has limited sensitivity (86%) and poor specificity (40%) for detecting ulcerations in active Crohn's colitis. 7
• CE cannot obtain tissue samples necessary for differentiating between infectious, inflammatory, ischemic, and neoplastic causes. 7
• CE is not indicated for overt lower GI bleeding with hematochezia. 7

Clinical Algorithm for CE Use

Step 1: Determine Primary Clinical Scenario

• Overt GI bleeding with negative EGD/colonoscopy → Proceed directly to CE within 48 hours 3
• Suspected Crohn's disease → Check fecal calprotectin, ensure NSAID abstinence ≥1 month, assess for obstructive symptoms 1
• Iron-deficiency anemia → Only if selected cases with high suspicion for small bowel source 1, 3

Step 2: Assess Stricture Risk

• No obstructive symptoms + suspected Crohn's disease → Proceed to CE (retention risk 3.6%) 1, 6
• Obstructive symptoms OR known stricturing disease → Perform patency capsule or cross-sectional imaging (MR/CT enterography) first 1, 6

Step 3: Interpret Results and Follow-Up

• Positive findings requiring intervention → Device-assisted enteroscopy for tissue sampling or therapy 3
• High-quality negative CE in suspected small-bowel bleeding → Conservative management 3
• Equivocal findings after cross-sectional imaging → CE as subsequent investigation if likely to influence management 3

Key Pitfalls to Avoid

• Do not perform CE without first completing high-quality EGD and colonoscopy in bleeding patients, as these procedures consistently reveal missed lesions. 3
• Do not rely on CE findings alone in NSAID users, as minor abnormalities may not represent true pathology. 1, 5
• Do not use CE as a first-line test in patients with obstructive symptoms, as this significantly increases retention risk. 1
• Do not substitute colon CE for standard colonoscopy when tissue diagnosis or therapeutic intervention may be needed. 1, 7
• Patients must be counseled about potential risks including failed procedure, capsule retention, and missed lesions. 1