Amebic Hepatic Abscesses Workup
- Author: Daniel Matei Brailita, MD; Chief Editor: BS Anand, MD more...
Approximately three fourths of patients with an amebic liver abscess have leukocytosis. This most likely will appear if symptoms are acute or complications have developed. However, eosinophilia is rare.
Anemia may be present, but the cause usually is multifactorial.
Hyperbilirubinemia is present in only a small proportion of cases.
In acute liver abscess, the aspartate aminotransferase (AST) levels are high. In chronic liver abscess, the alkaline phosphatase level tends to be elevated and the AST level tends to be within normal limits. Overall, the alkaline phosphatase level is elevated in about 70% of cases of amebic liver abscess.
Similar CBC count and liver test abnormalities are found in patients with pyogenic liver abscesses and are not specific.
The role of microscopic stool examination is limited. Less than 30-40% of patients with amebic liver abscess have concomitant intestinal amebiasis, and 10% of the population is infected with the nonpathogenic strain of E dispar. Hence, the microscopic examination of the stool for the identification of cysts is of little value. If positive, it may suggest the diagnosis.
Fecal findings suggestive of amebic colitis include a positive test for heme, a paucity of neutrophils, and the presence of Charcot-Leyden crystal protein. The stool examination is still of value if the serologic and antigen identification tests are not available.
Examination of the stool for hematophagous trophozoites of E histolytica must be made on at least 3 fresh specimens because the trophozoites are very sensitive and may be excreted intermittently. A combination of wet mount, iodine-stained concentrates, and trichrome-stained preparations is used.
Upon examination of the stool, trophozoites may be confused with neutrophils. Cysts must be differentiated morphologically from nonpathogenic Entamoeba hartmanni, Entamoeba coli, and Endolimax nana. Nonpathogenic E dispar cannot be differentiated morphologically and require fecal antigen detection.
Stool antigen detection
Stool antigen detection facilitates early diagnosis before an antibody response occurs (< 7 d) and differentiates pathogenic from nonpathogenic Entamoeba infection. The primary drawbacks are the requirement for fresh, unpreserved stool specimens and the lack of intestinal amebiasis in as many as 60% of patients with amebic liver abscess.
Stool antigen detection kits based on enzyme immunoassay (EIA) are most common and still quite sensitive compared to polymerase chain reaction (PCR)-based methods.
The PCR stool test shows high sensitivity for detecting E histolytica and for distinguishing nonpathogenic amoebas.[14, 15, 16] However, this test is expensive. Real-time (rapid) PCR is sensitive but not well standardized and is not widely available.
Stool culture for amoeba is sensitive but has limited availability.
Serologic testing is the most widely used method of diagnosis for amebic liver abscess. In general, the test result should be positive, even in cases when the result of the stool test is negative (only extraintestinal disease).
EIA has now largely replaced indirect hemagglutination (IHA) testing and counter immunoelectrophoresis (CIE) testing. EIA is relatively simple and easy to perform, rapid, inexpensive, and more sensitive.[19, 20]
The EIA test detects antibodies specific for E histolytica in approximately 95% of patients with extraintestinal amebiasis, in 70% of patients with active intestinal infection, and in 10% of persons who are asymptomatic cyst passers.
The EIA serology findings revert to negative in 6-12 months following eradication of infection. Even in highly endemic areas, fewer than 10% of patients who are asymptomatic have positive amebic serology findings.
Initial negative test results may appear in as many as 10% of patients with amebic liver abscess. Under these circumstances, order repeat serology testing in 1 week. This test result will usually be positive.
Serum antigen detection
E histolytica galactose lectin antigen is detectable by enzyme-linked immunosorbent assay (ELISA) in at least 75% of serum samples obtained from patients with amebic liver abscess. Studies reported an antigen seropositivity of 96% with a reversal rate of 82% after 1 week of treatment with metronidazole. This test may be useful for patients who present acutely, before an antibody response occurs. The sample needs to be obtained before starting the treatment, as the treatment leads to rapid antigen loss. This test can be used for rapid diagnosis in highly endemic areas, where serology can be misleading, but it is not widely available.
Rapid antigen and antibody tests are currently being evaluated and seem very promising.
None of the imaging tests can definitively differentiate among a pyogenic liver abscess, an amebic abscess, and malignant disease. Clinical, epidemiologic, and serologic correlation is needed for diagnosis.
Ultrasonography is the preferable initial diagnostic test. It is rapid, inexpensive, and is only slightly less sensitive than CT scan (75-80% sensitivity vs 88-95% for CT scan).
Ultrasonography simultaneously evaluates the gallbladder and avoids radiation exposure.
As opposed to scanning with technetium-99m, ultrasonography often can distinguish an abscess from a tumor or other solid focal lesion. The lesions tend to be round or oval, with well-defined margins, and hypoechoic.
Computed tomography scanning
CT scanning is sensitive but the findings are not specific. The abscess typically appears low density with smooth margins and a contrast-enhancing peripheral rim.
The use of injected contrast may differentiate hepatic abscesses from vascular tumors. See the images below.
Magnetic resonance imaging
MRI is sensitive, but the findings are not specific. This imaging modality provides information comparable with less expensive imaging procedures.
Nuclear imaging studies
Technetium-99m liver scanning is useful for differentiating an amebic liver abscess from a pyogenic abscess; however, it is not used as a first-line test.
Because amebic liver abscesses do not contain leukocytes, they appear as cold lesions on hepatic nuclear scanning, with a typical hot halo or a rim of radioactivity surrounding the abscess. In contrast, pyogenic liver abscesses contain leukocytes and, therefore, typically appear as hot lesions on nuclear scanning.
Gallium scanning is helpful in differentiating pyogenic abscess (similar to technetium-99m nuclear hepatic scanning) but requires delayed images, which makes the test less helpful.
Other imaging studies
Hepatic angiography is only useful to differentiate liver abscesses from vascular lesions.
Plain chest or abdominal films may show elevation and limitation of motion of the right diaphragm, basilar atelectasis, and right pleural effusion or gas within the abscess cavity.
Aspiration of the abscess content is indicated only if rupture of the abscess is thought to be imminent, differentiation between amebic abscess and pyogenic abscess is critical, or there is no response to antiprotozoal therapy in 5-7 days (see Surgical Care). Note the following:
Aspiration may be performed under CT scan or sonographic guidance.
Send the collected specimen for Gram stain and cultures.
Amebae rarely are recovered from the aspirate (15%) and, often, they are present only in the peripheral parts of the abscess, invading and destroying adjacent tissue.
Amebic liver abscesses only rarely yield positive bacterial cultures following secondary bacterial infection of the abscess cavity.
Detecting E histolytica antigen in the aspirate is possible and is accomplished as previously described for stool specimens. It is highly specific. The sensitivity was only 20% using ELISA, but newer PCR-based assays have a sensitivity of 83% and a specificity of 100%. [23, 24] However, currently, PCR-based detection is not widely available.
Many possible complications are associated with aspiration of the abscess, of which the most common are infection and bleeding. Other complications include amebic peritonitis or inadvertent puncture of an echinococcal cyst.
The liver involvement in amebiasis consists of necrotic abscesses and periportal inflammation. The abscess contains acellular proteinaceous debris and is surrounded by a rim of amebic trophozoites invading tissue. The abscess contains a chocolate-colored fluid that resembles anchovy paste and consists predominantly of necrotic hepatocytes. Triangular areas of hepatic necrosis, possibly due to ischemia from amebic obstruction of portal vessels, have been observed. E histolytica can also induce hepatocyte and neutrophilic apoptosis. Some authors postulate that amebic liver abscess probably results from the coalescence of small microabscesses. Periportal fibrosis may be present, but whether this represents prior trophozoite invasion or a host reaction to amebic antigens or toxins is not known.
Blazquez S, Rigothier MC, Huerre M, et al. Initiation of inflammation and cell death during liver abscess formation by Entamoeba histolytica depends on activity of the galactose/N-acetyl-D-galactosamine lectin. Int J Parasitol. 2007 Mar. 37(3-4):425-33. [Medline].
Stanley SL Jr. Amoebiasis. Lancet. 2003 Mar 22. 361(9362):1025-34. [Medline].
Acuna-Soto R, Maguire JH, Wirth DF. Gender distribution in asymptomatic and invasive amebiasis. Am J Gastroenterol. 2000 May. 95(5):1277-83. [Medline].
Blessmann J, Ali IK, Nu PA, et al. Longitudinal study of intestinal Entamoeba histolytica infections in asymptomatic adult carriers. J Clin Microbiol. 2003 Oct. 41(10):4745-50. [Medline].
Haque R, Duggal P, Ali IM, et al. Innate and acquired resistance to amebiasis in bangladeshi children. J Infect Dis. 2002 Aug 15. 186(4):547-52. [Medline].
Hoffner RJ, Kilaghbian T, Esekogwu VI, et al. Common presentations of amebic liver abscess. Ann Emerg Med. 1999 Sep. 34(3):351-5. [Medline].
Hughes MA, Petri WA Jr. Amebic liver abscess. Infect Dis Clin North Am. 2000 Sep. 14(3):565-82, viii. [Medline].
Ravdin JI. Amebiasis. Clin Infect Dis. 1995 Jun. 20(6):1453-64; quiz 1465-6. [Medline].
Ravdin JI, Stauffer W. Entamoeba histolytica (amebiasis). Mandell Gl, Bennett J, Dolin R eds. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, PA: Elsevier; 2005. Vol 2: Part III, sect H, 3097-3111.
Mbaye PS, Koffi N, Camara P, et al. [Pleuropulmonary manifestations of amebiasis]. Rev Pneumol Clin. 1998 Dec. 54(6):346-52. [Medline].
Tanyuksel M, Petri WA Jr. Laboratory diagnosis of amebiasis. Clin Microbiol Rev. 2003 Oct. 16(4):713-29. [Medline].
Solaymani-Mohammadi S, Rezaian M, Babaei Z, et al. Comparison of a stool antigen detection kit and PCR for diagnosis of Entamoeba histolytica and Entamoeba dispar infections in asymptomatic cyst passers in Iran. J Clin Microbiol. 2006 Jun. 44(6):2258-61. [Medline].
Hamzah Z, Petmitr S, Mungthin M, et al. Differential detection of Entamoeba histolytica, Entamoeba dispar, and Entamoeba moshkovskii by a single-round PCR assay. J Clin Microbiol. 2006 Sep. 44(9):3196-200. [Medline].
Khairnar K, Parija SC. A novel nested multiplex polymerase chain reaction (PCR) assay for differential detection of Entamoeba histolytica, E. moshkovskii and E. dispar DNA in stool samples. BMC Microbiol. 2007 May 24. 7:47. [Medline].
Roy S, Kabir M, Mondal D, et al. Real-time-PCR assay for diagnosis of Entamoeba histolytica infection. J Clin Microbiol. 2005 May. 43(5):2168-72. [Medline].
Qvarnstrom Y, James C, Xayavong M, et al. Comparison of real-time PCR protocols for differential laboratory diagnosis of amebiasis. J Clin Microbiol. 2005 Nov. 43(11):5491-7. [Medline].
Otto MP, Gerome P, Rapp C, et al. False-negative serologies in amebic liver abscess: report of two cases. J Travel Med. 2013 Mar-Apr. 20(2):131-3. [Medline].
Knobloch J, Mannweiler E. Development and persistence of antibodies to Entamoeba histolytica in patients with amebic liver abscess. Analysis of 216 cases. Am J Trop Med Hyg. 1983 Jul. 32(4):727-32. [Medline].
Restrepo MI, Restrepo Z, Elsa Villareal CL, et al. Diagnostic tests for amoebic liver abscess: comparison of enzyme-linked immunosorbent assay (ELISA) and counterimmunoelectrophoresis (CIE). Rev Soc Bras Med Trop. 1996 Jan-Feb. 29(1):27-32. [Medline].
Leo M, Haque R, Kabir M, et al. Evaluation of Entamoeba histolytica antigen and antibody point-of-care tests for the rapid diagnosis of amebiasis. J Clin Microbiol. 2006 Dec. 44(12):4569-71. [Medline].
Bammigatti C, Ramasubramanian N, Kadhiravan T, Das AK. Percutaneous needle aspiration in uncomplicated amebic liver abscess: a randomized trial. Trop Doct. 2013 Jan. 43(1):19-22. [Medline].
Khan U, Mirdha BR, Samantaray JC, et al. Detection of Entamoeba histolytica using polymerase chain reaction in pus samples from amebic liver abscess. Indian J Gastroenterol. 2006 Mar-Apr. 25(2):55-7. [Medline].
Singh P, Mirdha BR, Ahuja V, Singh S. Evaluation of small-subunit rRNA touchdown polymerase chain reaction for direct detection of Entamoeba histolytica in human pus samples from patients with amoebic liver abscess. Indian J Med Microbiol. 2011 Apr-Jun. 29(2):141-6. [Medline].
Khan R, Hamid S, Abid S, et al. Predictive factors for early aspiration in liver abscess. World J Gastroenterol. 2008 Apr 7. 14(13):2089-93. [Medline].
Khanna S, Chaudhary D, Kumar A, et al. Experience with aspiration in cases of amebic liver abscess in an endemic area. Eur J Clin Microbiol Infect Dis. 2005 Jun. 24(6):428-30. [Medline].
Blessmann J, Binh HD, Hung DM, et al. Treatment of amoebic liver abscess with metronidazole alone or in combination with ultrasound-guided needle aspiration: a comparative, prospective and randomized study. Trop Med Int Health. 2003 Nov. 8(11):1030-4. [Medline].
Maltz G, Knauer CM. Amebic liver abscess: a 15-year experience. Am J Gastroenterol. 1991 Jun. 86(6):704-10. [Medline].
Rajak CL, Gupta S, Jain S, et al. Percutaneous treatment of liver abscesses: needle aspiration versus catheter drainage. AJR Am J Roentgenol. 1998 Apr. 170(4):1035-9. [Medline].
Stanley SL Jr. Vaccines for amoebiasis: barriers and opportunities. Parasitology. 2006. 133 Suppl:S81-6. [Medline].
Snow MJ, Stanley SL Jr. Recent progress in vaccines for amebiasis. Arch Med Res. 2006 Feb. 37(2):280-7. [Medline].
Houpt E, Barroso L, Lockhart L, et al. Prevention of intestinal amebiasis by vaccination with the Entamoeba histolytica Gal/GalNac lectin. Vaccine. 2004 Jan 26. 22(5-6):611-7. [Medline].
Abd Alla MD, White GL, Rogers TB, et al. Adherence-inhibitory intestinal immunoglobulin a antibody response in baboons elicited by use of a synthetic intranasal lectin-based amebiasis subunit vaccine. Infect Immun. 2007 Aug. 75(8):3812-22. [Medline].
Ivory CP, Chadee K. Intranasal immunization with Gal-inhibitable lectin plus an adjuvant of CpG oligodeoxynucleotides protects against Entamoeba histolytica challenge. Infect Immun. 2007 Oct. 75(10):4917-22. [Medline].
Stanley SL Jr, Jackson TF, Foster L, et al. Longitudinal study of the antibody response to recombinant Entamoeba histolytica antigens in patients with amebic liver abscess. Am J Trop Med Hyg. 1998 Apr. 58(4):414-6. [Medline].