What are the differential diagnoses for melena?

Differential Diagnoses for Melena

The most common causes of melena are peptic ulcer disease (35-50%), gastroduodenal erosions (8-15%), and esophagitis (5-15%), with the upper gastrointestinal tract being the source in approximately 80% of cases. 1

Primary Differential Diagnoses (Upper GI Sources)

Based on British Society of Gastroenterology guidelines, the differential diagnosis for melena follows a clear hierarchy by frequency 1:

Most Common Causes (Upper GI Tract - ~80% of cases)

• Peptic ulcer disease (35-50%) - Most frequent cause, includes both gastric and duodenal ulcers
• Gastroduodenal erosions (8-15%) - Often NSAID-related or stress-induced
• Esophagitis (5-15%) - Reflux-related or pill esophagitis
• Mallory-Weiss tear (15%) - Typically preceded by forceful vomiting
• Esophageal or gastric varices (5-10%) - Consider in patients with liver disease or portal hypertension
• Upper gastrointestinal malignancy - Gastric or esophageal cancer
• Vascular malformations (1%) - Angiodysplasia, Dieulafoy lesions

Less Common Upper GI Causes

• Rare causes (5%) - Include gastric adenomyoma 2, duodenal metastases from lung cancer 3, and other unusual pathology

Secondary Sources (When Upper Endoscopy is Negative)

In 24% of patients presenting with melena, upper endoscopy will be nondiagnostic 4. In these cases:

Right Colon Sources (Most Likely Alternative)

• Right-sided colonic lesions - Identified in 37% of patients with negative upper endoscopy 4
• Colonic adenomas with bleeding - Can rarely present as melena 5
• Cecal or ascending colon pathology - Slow transit allows blood degradation

Small Bowel Sources

• Small intestinal bleeding - Identified in pediatric studies as a source when upper endoscopy negative 6
• Small bowel tumors or vascular lesions - Require capsule endoscopy or enteroscopy

Critical Clinical Distinctions

Patients presenting with both hematemesis and melena have more severe bleeding than those with melena alone 1. This distinction impacts urgency and management approach.

Important Pitfalls to Avoid

• Dietary mimics: Black stool from bismuth, iron supplements, or foods like chocolate cookies can mimic melena 7. True melena has a characteristic tarry consistency and distinctive odor.
• Assuming upper GI source: While most common, don't anchor on upper GI if endoscopy is negative—pursue colonoscopy next 4
• Missing right colon pathology: When upper endoscopy is negative, colonoscopy (not small bowel studies or angiography) has the highest yield 4

Diagnostic Algorithm

1. Initial assessment: Confirm true melena (tarry, black stool) vs. dietary mimic
2. First-line investigation: Esophagogastroduodenoscopy identifies source in ~76% of cases 4
3. If negative upper endoscopy: Proceed to colonoscopy (highest yield for right colon sources) 4
4. If both negative: Consider capsule endoscopy for small bowel evaluation 6
5. Pediatric considerations: In children with underlying conditions, duodenal ulcers are most common; look for vomiting, abnormal ultrasound, or hemoglobin ≤3 g/dL below normal as indicators of upper GI source 6

A cause for bleeding is ultimately identified in approximately 80% of cases when appropriate investigations are pursued 1.