Review Question - QID 220783

This patient with a history of diarrhea, right upper quadrant pain, fever, tachycardia, and an abscess on ultrasound most likely has Entamoeba histolytica amebiasis given his recent migration from central America. Empiric metronidazole should be administered to patients with suspected amebic liver abscess pending further diagnostic evaluation.

Entamoeba histolytica is the pathogen responsible for amebic liver abscesses. This organism is transmitted by oral ingestion of food or water contaminated with cysts. It is endemic to Central and South America, Africa, and Asia. Findings of an amebic liver abscess include right upper quadrant pain, cough, sweating, malaise, weight loss, fever, jaundice, and hepatomegaly. Ultrasound and serum anti-amebic IgG levels can be used to support the diagnosis. Patients with an amebic liver abscess should be treated with metronidazole or tinidazole empirically. An alternative therapy is nitazoxanide. Routine aspiration of the abscess is not required. In addition, paromomycin, diiodohydroxyquin, or diloxanide furoate can be administered in order to eliminate any intraluminal cysts that exist in these patients.

Chavez-Tapia et al. review the evidence regarding image-guided percutaneous aspiration plus metronidazole compared to metronidazole alone for uncomplicated amebic liver abscesses. They discuss how there is insufficient evidence to conclude whether therapeutic aspiration hastens clinical or radiological resolution of amebic liver abscesses. They recommended that further randomized controlled trials be performed to answer this question.

Figure/Illustration A demonstrates an ultrasound of the right upper quadrant of the abdomen with a hypoechoic region (red circle). This finding is consistent with an irregular pus-filled cavity that would be caused by Entamoeba histolytica infection.

Incorrect Answers:
Answer 1: Colonoscopy can be performed to confirm the diagnosis of intestinal amebiasis, which presents with abdominal pain, diarrhea, and bloody stools. Simultaneous intestinal and extraintestinal infection with Entamoeba histolytica occurs in fewer than 1/3 of cases. Colonoscopy is not an appropriate routine diagnostic tool since amebic ulcerations increase the likelihood of perforation during this procedure.

Answer 2: Cyst aspiration is not required in uncomplicated amebic liver abscesses as it does not yield additional useful diagnostic information. In cases where an amebic liver abscess is suspected, empiric therapy with metronidazole should be initiated pending further diagnostic investigation. The confirmatory test would be serum antibody levels.

Answer 4: Serum antibody labs help secure the diagnosis of amebic liver abscesses; however, empiric therapy with metronidazole should be initiated in suspected cases pending further diagnostic evaluation.

Answer 5: Stool microscopy can supplement serologic or antigenic testing to confirm the diagnosis of amebiasis. However, metronidazole should be initiated empirically pending further diagnostic evaluation. In addition, simultaneous liver abscess and amebic colitis are uncommon, so stool microscopy is usually negative in the setting of liver disease.

Bullet Summary:
Patients who are suspected to have an amebic liver abscess should be treated empirically with metronidazole prior to further diagnostic testing.