What is the differential diagnosis and management for a patient presenting with melena (dark blood in the stool)?

Differential Diagnosis and Management of Melena (Dark Blood in Stool)

Most Common Causes by Location

Melena indicates digested blood from the upper gastrointestinal tract, with peptic ulcers being the most frequent cause, followed by gastroduodenal erosions, esophagitis, varices, and Mallory-Weiss tears. 1

Upper GI Sources (Most Common)

• Peptic ulcer disease - the leading cause of melena 1
• Gastroduodenal erosions 1
• Esophagitis 1
• Varices (especially in cirrhotic patients with 30% mortality) 1
• Mallory-Weiss tears 1
• Cameron's erosions in large hiatal hernias (commonly overlooked) 2
• Gastric antral vascular ectasia 2
• Dieulafoy's lesion 2
• Fundic varices 2

Small Bowel Sources (5% of Cases)

• Angiodysplasia - accounts for up to 80% of obscure bleeding, particularly in patients >40 years 2, 3
• Small bowel tumors - most common cause in patients <50 years 2
• NSAID-induced ulcers 2
• Crohn's disease (younger patients) 2
• Hemobilia, hemosuccus pancreaticus (C-loop duodenum) 2
• Aortoenteric fistula (patients with prior AAA repair) 2, 4

Rare Lower GI Sources

• Slow bleeding from right colon can occasionally produce dark stools (not true melena) 1

Immediate Assessment and Resuscitation

Hemodynamic Evaluation

• Calculate shock index (heart rate/systolic BP) immediately - a value >1 indicates hemodynamic instability and predicts poor outcomes 5
• Check for orthostatic hypotension indicating significant blood loss requiring ICU admission 5
• Assess pulse >100 bpm, systolic BP <100 mmHg, hemoglobin <100 g/L as markers of severe bleeding 1

Resuscitation Protocol

• Establish two large-bore IV lines in anticubital fossae and begin aggressive fluid resuscitation with normal saline before any diagnostic procedures 1
• Infuse 1-2 liters normal saline initially in hemodynamically compromised patients 1
• Add plasma expanders if shock persists after 2 liters (indicates ≥20% blood volume loss) 1
• Transfuse red blood cells to maintain hemoglobin >7 g/dL (or >9 g/dL with massive bleeding or cardiovascular comorbidities) 1, 5
• Transfuse fresh frozen plasma if INR >1.5 5
• Transfuse platelets if count <50,000/µL 5
• Insert urinary catheter and monitor hourly urine output (target >30 ml/h) 1

Diagnostic Approach

For Hemodynamically Stable Patients

• Perform esophagogastroduodenoscopy (EGD) first as the initial procedure of choice - it has both diagnostic and therapeutic capabilities 1, 5, 6
• Ideally perform early elective endoscopy within 24 hours of admission 1
• Use cap-fitted endoscopy to examine blind areas (high lesser curve, under incisura angularis, posterior duodenal bulb) 2
• Obtain random duodenal biopsies for celiac disease 2
• Use side-viewing endoscope to examine ampulla if indicated 2

For Hemodynamically Unstable Patients (Shock Index >1)

• Perform CT angiography immediately - this provides the fastest, least invasive means to localize active bleeding 5
• Following positive CTA, proceed to catheter angiography with embolization within 60 minutes 5
• Critical pitfall: Do NOT perform endoscopy before adequate resuscitation - this increases mortality 1

If Initial EGD and Colonoscopy Are Negative

• Proceed to capsule endoscopy to identify small intestinal bleeding lesions 2
• Review capsule endoscopy in its entirety as it may provide clues to bleeding from stomach and colon overlooked by conventional endoscopy 2
• Consider double-balloon enteroscopy for therapeutic intervention if lesion identified 2
• Be aggressive investigating younger patients (<50 years) as small bowel tumors are the most common cause in this age group 2

Post-Endoscopy Management

After Successful Endoscopic Therapy

• Administer high-dose proton pump inhibitor therapy following successful endoscopic treatment of ulcer bleeding 1
• Address underlying causes: Helicobacter pylori eradication, acid suppression 1
• Counsel regarding NSAID use 1

Anticoagulation Management

• If on warfarin, interrupt immediately and reverse with prothrombin complex concentrate and vitamin K for unstable hemorrhage 5
• If on aspirin for primary prophylaxis, permanently discontinue 5
• If on aspirin for secondary prevention, restart as soon as hemostasis is achieved (do not routinely stop) 5

Special Populations

Cirrhotic Patients

• Variceal bleeding mortality approaches 30% versus 10% for nonvariceal sources - requires early identification and specialized management 1
• Consider early TIPS placement in Child-Pugh class C (score 10-13) or class B with active bleeding despite vasoactive agents 1

Elderly Patients (>65 Years)

• Significantly higher mortality rates requiring more aggressive management 1, 7
• More prone to bleeding from vascular lesions (up to 40% of causes in patients >40 years) 2

Patients with Prior AAA Repair

• Maintain high suspicion for aortoenteric fistula - universally deadly if left untreated 4
• Often presents with herald bleed before life-threatening hemorrhage 4

Critical Pitfalls to Avoid

• Failure to consider upper GI source in patients with melena and hemodynamic instability leads to delayed diagnosis - always perform upper endoscopy first 5
• Do not delay resuscitation to obtain imaging in unstable patients - stabilize first, then image 5
• Nuclear medicine scans and angiography should not be completely relied upon for diagnosis 4
• If patient remains unstable despite aggressive resuscitation, proceed directly to surgery rather than pursuing further diagnostic studies 5
• Avoid hyperventilation during resuscitation as it is associated with increased mortality in hemorrhagic shock 1
• Consider endotracheal intubation before endoscopy in severely bleeding patients to prevent pulmonary aspiration 1