A 26-year-old man comes to the clinic due to a 2-week history of persistent abdominal pain in the right upper quadrant, low-grade fever, and anorexia. The patient recently emigrated from Mexico, where he worked as a mechanic. For several days 3 months ago, he had bloody diarrhea, which resolved spontaneously. He takes no medications or herbal preparations. The patient has had no other travel, exposure to animals, or sick contacts. Temperature is 38.7 C (101.7 F), blood pressure is 122/80 mm Hg, pulse is 82/min, and respirations are 14/min. Physical examination shows tenderness to palpation in the right upper quadrant but is otherwise unremarkable. There is no jaundice. Laboratory results are as follows:
| Complete blood count | |
| Hemoglobin | 14.2 g/dL |
| Platelets | 310,000/mm3 |
| Leukocytes | 11,800/mm3 |
| Neutrophils | 65% |
| Eosinophils | 1% |
| Lymphocytes | 30% |
| Monocytes | 4% |
| Liver function test | |
| Alkaline phosphatase | 300 U/L |
CT scan of the abdomen reveals a 2 × 3 cm cystic lesion in the right lobe of the liver. Blood cultures are obtained. Which of the following is the most appropriate next step in management of this patient?
Entamoeba histolytica | |
Risk factors |
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Clinical manifestations |
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Diagnosis |
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Treatment |
PLUS
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*Does not distinguish between prior & current infection. RUQ = right upper quadrant. | |
This patient has fever, right upper quadrant pain, and a cystic hepatic lesion, findings worrisome for a liver abscess. With the history of bloody diarrhea and recent emigration from a resource-limited country, this presentation suggests Entamoeba histolytica infection (amebiasis), a protozoan infection typically acquired via contamined food or water.
E histolytica infection is usually asymptomatic but can result in amebic colitis (eg, bloody diarrhea) or extraintestinal disease via hematogenous spread to the liver, lungs, or brain. The most common extraintestinal manifestation is a liver abscess, which may present weeks to months after initial infection. Like other causes of liver abscess (eg, bacterial), amebic liver abscesses cause fever, right upper quadrant pain, and elevated liver enzymes, particularly alkaline phosphatase. Leukocytosis, often without left shift, may be present. Eosinophilia, usually seen in helminthic (rather than protozoal) infections, is not characteristic. Concurrent diarrhea is usually absent, but a prior history of bloody stools may be elicited.
In patients in whom amebiasis is suspected and who have active diarrhea, stool antigen or PCR testing is preferred (sensitive and specific). Stool microscopy (eg, ova and parasites) looking for cysts and trophozoites is sometimes the only diagnostic tool available but has low sensitivity, often requires multiple specimens, and is operator dependent (Choice B). In contrast, in patients such as this one with a liver abscess and no concurrent diarrhea, preferred diagnostic testing is serology, although it cannot differentiate between prior and current infection.
(Choices A and C) Percutaneous aspiration/drainage and intravenous antibiotics (eg, ceftriaxone) are treatments for bacterial liver abscesses. These typically occur in the setting of biliary infection or hematogenous spread of intraabdominal infections in elderly patients with underlying comorbidities (eg, diabetes mellitus); patients are usually jaundiced and ill-appearing. In contrast, management of amebic liver abscesses is an oral tissue agent (eg, metronidazole) and a luminal agent (ie, paromomycin) to eradicate intestinal colonization. Drainage has not been shown to improve outcomes compared to medical therapy and is reserved for those whose condition fails to improve with initial therapy or who have large (>10 cm) lesions at risk of imminent rupture.
(Choice E) Surgical resection may be indicated for hepatic cysts caused by Echinococcus; however, small cysts (<10 cm) are typically asymptomatic, and eosinophilia would be expected.
Educational objective:
Entamoeba histolytica infection should be considered in patients with a liver abscess (eg, fever, right upper quadrant pain, cystic hepatic lesion) who have traveled in a resource-limited country; a prior history of bloody diarrhea is common. Serologic testing is the preferred diagnostic modality in the absence of concurrent diarrhea.