Diseases Causing Black Tarry Stools (Melena)
The most common causes of melena are peptic ulcer disease (duodenal and gastric ulcers), gastric erosions, and esophageal varices, with the upper gastrointestinal tract being the source in the vast majority of cases. 1
Upper Gastrointestinal Sources (Most Common)
The upper GI tract (proximal to the ligament of Treitz) accounts for the overwhelming majority of melena cases 1:
Peptic Ulcer Disease
- Duodenal ulcers are the single most common cause of melena 1, 2
- Gastric ulcers are the second most frequent ulcer-related cause 1, 2
- These account for a substantial proportion of all melena presentations 2
Gastric and Esophageal Lesions
- Gastric erosions (erosive gastritis) are among the top causes 1, 3
- Esophagitis can cause significant bleeding presenting as melena 1, 2
- Esophageal varices are a critical cause, particularly in patients with portal hypertension 1, 2
- Mallory-Weiss tears from forceful vomiting 1
Vascular and Rare Upper GI Causes
- Angiodysplasia and vascular malformations in the upper GI tract 1
- Dieulafoy lesion accounts for 1-2% of acute upper GI bleeding 1
- Neoplasms of the esophagus, stomach, or duodenum 1
- Hemobilia (bleeding into the biliary tree) 1
- Hemosuccus pancreaticus (bleeding from the pancreatic duct), estimated at 1 in 500 cases 1
Iatrogenic and Post-Procedural
- Post-endoscopic biopsy bleeding 1
- ERCP-related injury 1
- Complications from biliary stenting 1
- Post-pancreatic surgery arterial injury 1
Small Intestinal Sources (Less Common)
When upper endoscopy is nondiagnostic, small bowel pathology should be considered 1, 2:
- Angiectasias account for up to 80% of obscure bleeding cases 1
- Small bowel tumors, particularly important in patients younger than 50 years 1
- Small intestinal ulcers or erosions 2
- Parasitic infections such as severe Strongyloidiasis causing duodenal ulceration 4
Lower Gastrointestinal Sources (Rare for Melena)
While uncommon, colonic sources can occasionally present with melena 5:
- Right-sided arteriovenous malformations 5
- Colitis 5
- Large polyps (≥20 mm) 5
- Colon tumors (patients with melena have increased colorectal cancer risk) 5
- Colonic ulcers 5
However, colonoscopy after nondiagnostic upper endoscopy has a diagnostic yield of only 4.8% and therapeutic intervention rate of just 1.7% 5
Important Clinical Considerations
Risk Factors and Underlying Conditions
- Patients with severe underlying diseases have increased bleeding tendency 3
- Alcohol consumption and NSAID/medication use are common precipitants 3
- Patients with malignancy or severe mental/physical disorders are at higher risk 2
Key Diagnostic Indicators
In pediatric populations (principles applicable to adults), factors suggesting upper GI source identifiable on endoscopy include 2:
- Vomiting accompanying melena
- Abnormal abdominal imaging findings
- Hemoglobin ≥3 g/dL below normal limit
Critical Pitfall to Avoid
Black licorice ingestion can mimic melena appearance and also potentiates anticoagulation in patients on warfarin, creating a confounding clinical picture 6. Always obtain dietary history before extensive workup.
Diagnostic Approach Algorithm
Esophagogastroduodenoscopy (EGD) is the primary diagnostic modality for melena, as the upper GI tract is the source in most cases 1, 2
For nondiagnostic initial EGD, consider repeat endoscopy with enhanced techniques: cap-fitted endoscopy for blind areas, side-viewing scope for ampulla, push enteroscopy for deep duodenum, and random duodenal biopsies for celiac disease 1
If upper endoscopy remains negative, proceed to capsule endoscopy for small bowel evaluation, which has revolutionized obscure bleeding diagnosis 1, 2
Colonoscopy should be performed in stable patients without active bleeding, primarily for colorectal cancer screening given increased risk, though diagnostic yield for melena source is low 5
For active bleeding with negative endoscopy, CT angiography or visceral arteriography are appropriate 1