What are the possible causes of melena?

Differential Diagnosis of Melena

Melena indicates digested blood in the gastrointestinal tract and most commonly originates from peptic ulcer disease, gastroduodenal erosions, esophagitis, varices, and Mallory-Weiss tears, with the upper GI tract being the source in approximately 85-90% of cases. 1, 2

Upper Gastrointestinal Sources (Most Common)

High-Frequency Causes

• Peptic ulcer disease accounts for 35-50% of all upper GI bleeding cases, representing the leading nonvariceal cause, typically associated with Helicobacter pylori infection or chronic NSAID use 3, 1
• Gastroduodenal erosions cause 8-15% of cases, commonly linked to NSAID use, stress, or metabolic conditions like diabetes 3
• Mallory-Weiss tears account for approximately 15% of cases, characteristically occurring after forceful vomiting or retching episodes 3, 1
• Esophagitis accounts for 5-15% of cases 3
• Esophageal varices cause 5-10% of upper GI bleeding overall, though when present they more commonly cause massive hematemesis rather than melena 3

Commonly Overlooked Upper GI Causes

• Cameron's erosions in large hiatal hernias are frequently missed, particularly in patients with upper gastrointestinal symptoms 1
• Gastric antral vascular ectasia often associated with chronic kidney disease and cirrhosis 1
• Dieulafoy's lesion accounts for 1-2% of acute bleeding, consisting of a tortuous submucosal artery penetrating through the mucosa, commonly at the posterior gastric wall 3, 1

Rare but Critical Upper GI Causes

• Aortoenteric fistula should be suspected in patients with prior abdominal aortic aneurysm repair—this is a life-threatening emergency 1, 3
• Hemobilia and hemosuccus pancreaticus together account for roughly 1 in 500 cases of upper GI bleeding 1, 3
• Upper GI malignancy and vascular malformations each represent approximately 1% of cases 3

Small Bowel Sources (When Upper Endoscopy is Negative)

The presence of melena doubles the odds of finding a bleeding site within the proximal small intestine among patients with obscure gastrointestinal bleeding. 4

• Angiodysplasia accounts for up to 80% of obscure bleeding, particularly in patients over 40 years old 1
• Small bowel tumors are the most common cause of melena in patients under 50 years old, including GISTs, primary malignancies, and metastatic lesions 1, 5
• NSAID-induced ulcers in the small bowel 1
• Crohn's disease, particularly in younger patients with inflammatory bowel disease history 1

Lower Gastrointestinal Sources (Approximately 10-15% of Melena Cases)

When upper endoscopy fails to locate a bleeding source, colonoscopy should be performed because approximately 10-15% of patients presenting with melena have a lower GI origin. 1

• Diverticulosis is the most common lower-GI source in older adults, accounting for 20-41% of lower GI bleeding cases, with incidence rising over 200-fold from the third to eighth decade of life 1
• Angiodysplasia contributes to 3-40% of lower GI bleeding 1
• Ischemic colitis represents 10-21% of lower GI bleeding episodes, occurring more frequently in elderly individuals with cardiovascular disease 1
• Colorectal cancer or adenomatous polyps account for 6-27% of cases, with prevalence increasing in older populations 1

Diagnostic Algorithm

Initial Evaluation

• Confirm true melena by assessing for black, tarry appearance with sticky consistency and characteristic odor—simple black stools from dietary causes (iron supplements, bismuth, activated charcoal) lack this tarry quality 2, 1
• Assess hemodynamic status immediately: pulse >100 bpm and systolic BP <100 mmHg indicate severe bleeding requiring intensive monitoring 1, 3
• Obtain medication history specifically for NSAIDs, anticoagulants (warfarin, DOACs), and antiplatelet agents 1, 3

Endoscopic Approach

• Esophagogastroduodenoscopy (EGD) is the initial procedure of choice as it has both diagnostic and therapeutic capabilities, ideally performed within 24 hours of admission in hemodynamically stable patients 1, 2
• Use cap-fitted endoscopy to examine blind areas including the high lesser curve, under incisura angularis, and posterior duodenal bulb to improve diagnostic yield 1
• Obtain random duodenal biopsies for celiac disease evaluation 1

When Upper Endoscopy is Negative

• Proceed to capsule endoscopy to identify small intestinal bleeding lesions 1
• Review capsule endoscopy in its entirety, as it may provide clues to bleeding from stomach and colon overlooked by conventional endoscopy 1
• Consider double-balloon enteroscopy for therapeutic intervention if a lesion is identified 1
• Perform colonoscopy as approximately 10-15% of melena originates from the lower GI tract 1

High-Risk Features Requiring Aggressive Management

• Age >65 years confers markedly higher mortality, reaching up to 30% in those older than 90 years 1, 2
• Significant comorbidities (cardiovascular disease, renal insufficiency, liver disease, advanced malignancy) are the strongest predictors of death 1
• Hemodynamic instability (heart rate >100 bpm and systolic BP <100 mmHg) combined with active ulcer bleeding confers approximately 80% risk of ongoing bleeding or death 1
• Cirrhosis requires specialized management as variceal bleeding mortality approaches 30% versus 10% for nonvariceal sources 1

Critical Pitfalls to Avoid

• Never perform endoscopy before adequate resuscitation—this is a critical error that increases mortality 1
• Do not assume all black stools represent melena—obtain detailed medication and dietary history 2
• Do not delay endoscopy beyond 24 hours, as diagnostic and therapeutic success rates are highest within the first 36 hours 2
• Be aggressive in investigating younger patients (<50 years) as small bowel tumors are the most common cause in this age group 1
• Consider aortoenteric fistula in any patient with prior AAA repair presenting with melena—this is a surgical emergency 1, 3