A 36-year-old man comes to the emergency department due to a week of progressive right upper quadrant pain, malaise, anorexia, and fever. Three months ago, he returned from a vacation in Nepal, where he hiked in the mountains. During his trip, the patient had several self-resolving episodes of diarrhea. He also had unprotected sexual intercourse with a woman he met during the trip. He received no prophylactic vaccinations or oral medications prior to travel. Temperature is 38.5 C (101.3 F), blood pressure is 120/70 mm Hg, and pulse is 96/min. Breath sounds are decreased in the right lung base. The liver is palpable 3 cm below the right costal margin with a tender, smooth edge. There is no splenomegaly. Laboratory results are as follows:
| Leukocytes | 13,000/mm3 |
| Neutrophils | 67% |
| Eosinophils | 2% |
| Lymphocytes | 31% |
| Liver function studies | |
| Total bilirubin | 1.3 mg/dL |
| Alkaline phosphatase | 320 U/L |
| Aspartate aminotransferase (SGOT) | 87 U/L |
| Alanine aminotransferase (SGPT) | 99 U/L |
Abdominal ultrasonography reveals a small, solitary hypoechoic lesion on the right lobe of the liver. Which of the following is the most likely cause of this patient's condition?
Entamoeba histolytica | |
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PLUS
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*Does not distinguish between prior & current infection. RUQ = right upper quadrant. | |
This patient has fever, right upper quadrant (RUQ) pain, and a hepatic lesion, findings suggestive of liver abscess. He also has a history of recent travel to a resource-limited country. This presentation is concerning for amebiasis (infection due to Entamoeba histolytica).
Amebic liver abscesses develop when the ingested protozoan spreads from the colonic mucosa to the liver via the portal vein. The greater blood supply of the right lobe of the liver compared to the left explains the characteristic finding of a single, subcapsular, low-density lesion in the right lobe. Patients may have a history of colitis, but extraintestinal disease can occur without concurrent diarrhea or a classic diarrheal history.
Symptoms of amebic liver abscesses are subacute and include fever, hepatomegaly, and RUQ pain that may be referred to the right chest wall or shoulder. A right-sided sympathetic pleural effusion can be present due to diaphragmatic irritation from the hepatic lesion and is likely the cause of this patient's decreased breath sounds. Elevations in leukocyte count, alkaline phosphatase, and transaminases are typical. As with other protozoal infections (eg, giardiasis), peripheral eosinophilia is not a frequent finding (in contrast to many helminthic infections, which can stimulate IL-5 production).
(Choice A) Inflammation of the liver capsule in gonococcal perihepatitis (Fitz-Hugh–Curtis syndrome) can cause RUQ pain and fever. However, this is a complication of pelvic inflammatory disease, a condition not seen in men.
(Choice B) Hepatotropic viruses (eg, hepatitis A) are often acquired while traveling; acute infection can manifest with RUQ pain. However, jaundice and markedly elevated aminotransferases (often >1,000 U/L) would be expected, and an abscess would not be seen.
(Choice C) Malaria causes fever and jaundice after travel to a resource-limited country; however, splenomegaly would be expected, fever is cyclical, and hepatic abscesses are not typical.
(Choice D) Polymicrobial pyogenic (bacterial) abscesses share similar clinical and radiographic features with amebic abscesses but typically occur in patients who are ill-appearing, are elderly, and have comorbidities (eg, diabetes mellitus). The absence of these findings plus the patient's recent travel make amebiasis more likely.
(Choice F) Echinococcus can cause a hydatid liver cyst, but patients are usually asymptomatic. Large (>10 cm) cysts may cause RUQ pain and hepatomegaly, but fever is rare in the absence of cyst rupture, which is not seen on this patient's imaging. In addition, peripheral eosinophilia would be expected.
Educational objective:
Entamoeba histolytica, a protozoan, can cause colitis or extraintestinal disease (eg, liver abscess) after travel to a resource-limited country. Amebic liver abscess causes right upper quadrant pain, fever, and a subcapsular lesion in the right lobe.