Can intestinal parasitism cause melena?

Can Intestinal Parasitism Cause Melena?

Yes, intestinal parasitism can cause melena, though it is an uncommon presentation that typically occurs with heavy helminth infections, particularly hookworm and roundworm (Ascaris), which can cause acute gastrointestinal bleeding in addition to the more typical chronic occult blood loss.

Parasites That Can Cause Melena

Hookworm (Ancylostoma duodenale and Necator americanus)

• Hookworm is the most well-documented parasitic cause of melena, with case reports demonstrating acute massive gastrointestinal bleeding requiring multiple blood transfusions 1, 2
• Heavy hookworm infections typically cause chronic blood loss leading to iron deficiency anemia, but can present with overt melena in severe cases 3, 4
• Push enteroscopy in patients with melena and negative upper endoscopy has revealed fresh blood in the jejunum, multiple erosions, and visible hookworms 2
• The mechanism involves adult worms attaching to the intestinal mucosa and causing direct blood loss 4

Roundworm (Ascaris lumbricoides)

• Ascaris can cause acute gastrointestinal bleeding with melena, though this is less common than with hookworm 2
• Enteroscopy has identified roundworms in the jejunum of patients presenting with melena and hemoglobin as low as 2.8 g/dL 2
• While typically asymptomatic or causing abdominal pain and obstruction, heavy infections can result in intestinal bleeding 3

Schistosomiasis

• Chronic colonic ulceration from schistosomiasis can cause intestinal bleeding and iron deficiency anemia, though melena is not the typical presentation 3
• Very heavy acute infections can manifest as dysenteric illness with bleeding 3

Clinical Context and Diagnostic Approach

When to Suspect Parasitic Causes

• Consider parasitic infection in patients with melena from developing countries or with recent travel to endemic areas 1, 2
• Agricultural workers using waste water for irrigation are at particularly high risk for hookworm 1
• The diagnosis is often delayed because other causes (peptic ulcer disease, malignancy) are prioritized in older patients 1

Diagnostic Yield

• In patients with melena and nondiagnostic upper endoscopy, the diagnostic yield of colonoscopy is only 4.8%, making parasitic causes a relatively uncommon but important consideration 5
• Push enteroscopy evaluating the proximal 40-50 cm of jejunum is superior to standard endoscopy for identifying worms as the bleeding source 2
• Concentrated stool microscopy should be performed, though it may have low sensitivity 3, 4

Treatment Approach

Immediate Management

• Treat with mebendazole 100 mg twice daily for 3 days for both hookworm and roundworm when identified as the cause of bleeding 2
• Alternative regimens include albendazole 400 mg as a single dose for Ascaris or albendazole 400 mg daily for 3 days for hookworm 3
• Provide iron supplementation and folic acid for associated anemia 4, 2
• Blood transfusion may be necessary in severe cases with hemoglobin <3 g/dL 4, 2

Expected Outcomes

• Gastrointestinal bleeding typically subsides after appropriate antiparasitic treatment 2
• Endoscopic retrieval of worms can be attempted but is not always successful 2

Important Clinical Pitfalls

• Do not dismiss parasitic causes in older patients presenting with melena, as the focus on peptic ulcer disease and malignancy can delay diagnosis and increase financial burden 1
• Standard upper endoscopy will miss small bowel sources of bleeding from parasites; consider push enteroscopy in endemic populations 2
• While chronic occult bleeding is well-known with worm infestations, acute massive bleeding is rarely described but does occur 2
• Most parasitic intestinal infections present with nonbloody watery diarrhea rather than melena 3, 6