What are the causes of melena?

Causes of Melena

Melena results from bleeding in the upper gastrointestinal tract (proximal to the ligament of Treitz), with peptic ulcer disease being the most common cause, accounting for 35-50% of cases, followed by gastroduodenal erosions, esophagitis, varices, and Mallory-Weiss tears. 1, 2

Primary Upper GI Causes (Most Common)

Peptic Ulcer Disease

• Accounts for 35-50% of all melena cases, making it the leading nonvariceal cause 2
• Typically associated with Helicobacter pylori infection or chronic NSAID use 3, 2

Gastroduodenal Erosions

• Cause 8-15% of cases, commonly linked to NSAID use, stress, or metabolic conditions like diabetes 2

Esophagitis

• Accounts for 5-15% of cases and more frequently presents as coffee ground emesis rather than frank hematemesis 2

Esophageal Varices

• Cause 5-10% of upper GI bleeding overall, but when present, cause massive hematemesis (66-70% of massive cases) rather than typical melena 2, 4
• Require underlying portal hypertension from cirrhosis or chronic liver disease 5

Mallory-Weiss Tears

• Account for approximately 15% of cases, characteristically occurring after forceful vomiting or retching episodes 2, 5

Less Common Upper GI Causes

Vascular and Structural Lesions

• Cameron's erosions in large hiatal hernias are commonly overlooked 1
• Gastric antral vascular ectasia (GAVE), often associated with chronic kidney disease and cirrhosis 1
• Dieulafoy's lesion (1-2% of cases): a large caliber tortuous submucosal artery penetrating the mucosa, commonly at the posterior gastric wall 1, 2
• Angiodysplasia accounts for up to 80% of obscure bleeding, particularly in patients over 40 years old 1

Neoplastic Causes

• Upper GI malignancy represents approximately 1% of cases 2
• Hepatocellular carcinoma eroding into the duodenum 2

Rare but Critical Causes

• Aortoenteric fistula, particularly in patients with prior abdominal aortic aneurysm repair 3, 1, 2
• Hemobilia and hemosuccus pancreaticus (1 in 500 cases of upper GI bleeding) 3, 1, 2

Iatrogenic Causes

• Endoscopic ultrasound-guided biopsies, ERCP-related injury, delayed hemorrhage from biliary metallic stenting, and nitinol esophageal stent placement 2
• Extrahepatic arterial injury after pancreatic surgery 2

Small Bowel Causes (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 GI bleeding. 6

• Small bowel tumors are the most common cause in patients under 50 years old 1
• Angiodysplasia accounts for up to 80% of obscure bleeding in patients over 40 years 1
• NSAID-induced ulcers in the small bowel 1
• Crohn's disease, particularly in younger patients 1

Lower GI Causes (When Upper Endoscopy is Negative)

Approximately 10-15% of patients presenting with melena have a lower GI origin of bleeding, requiring colonoscopy when upper endoscopy is negative. 1

• Diverticulosis is the most common lower GI source, accounting for 20-41% of 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, more frequent in elderly with cardiovascular disease 1
• Colorectal cancer or adenomatous polyps account for 6-27% of cases 1

Critical Clinical Pitfalls

Distinguishing True Melena

• Black stools lacking the sticky, tar-like consistency and characteristic odor do not represent digested blood and generally do not require urgent GI evaluation unless other concerning features are present 1
• Obtain detailed medication and dietary history to identify non-bleeding causes (iron supplements, bismuth, activated charcoal) 1

Rapid Transit Considerations

• Massive upper GI bleeding can present as bright red blood per rectum (hematochezia) rather than melena if transit time is rapid enough 1
• Slow bleeding from the right colon can occasionally produce dark stools, though typically not true melena 1

High-Risk Populations

• Patients aged >65 years experience markedly higher mortality from melena, reaching up to 30% in those older than 90 years, requiring more aggressive therapeutic strategies 1
• Serious comorbid conditions (cardiovascular disease, renal insufficiency, liver disease, advanced malignancy) are the strongest predictors of death; virtually all fatalities occur in patients with such significant medical illnesses 1
• Hemodynamic instability (heart rate >100 bpm and systolic BP <100 mmHg) confers an approximately 80% risk of ongoing bleeding or death when combined with active ulcer bleeding 1