Amebic liver abscess results as a complication of an amebic infection. It is diagnosed through evaluation of clinical and epidemiologic factors as well as serologic and possibly imaging studies.
Amebic liver abscess is a complication of amebiasis, which is transmitted via the feco-oral route through infected humans [1]. The incubation period of amebiasis spans from 1 to 4 weeks [2] although it can take days to years [3]. Risk factors for amebic liver abscess include oral-anal intercourse in homosexual men [4], poor hygiene, overcrowding, immigration from endemic regions, and immunosuppression.
The clinical picture is variable, which makes the diagnosis challenging [5]. Amebic liver abscess in endemic regions is associated with an acute illness consisting of fever, weight loss, and abdominal pain [5]. The latter is characterized as a dull, achy, and unremitting pain in the right upper quadrant (RUQ) that radiates to right shoulder or scapula. Pain exacerbation occurs with deep inspiration and coughing. Other manifestations include rigors, nausea, emesis, and diarrhea. Patients may also report a history of dysentery [1]. A minority of patients will exhibit pulmonary symptoms such as coughing and chest pain. When a bronchopleural fistula forms, the productive cough yields brown paste-like substance [6].
Complications
Although uncommon, complications include peritoneal rupture and/or involvement of organs such as the heart and lungs.
Physical exam
Fever is noted in nearly all patients. Remarkable signs on the physical exam include hepatomegaly and tenderness in the RUQ and possibly epigastric region. Also, patients with pulmonary involvement will exhibit rales and diminished breath sounds at the right lung base upon auscultation. If present, peritoneal signs include rebound tenderness, guarding, as well as the absence of bowel sounds. Finally, pleural rub and/or pericardial rub are heard in those with complications.
Patients suspected to have an amebic hepatic abscess are assessed with a review of their personal history and risk factors, physical exam findings, and the appropriate studies.
Laboratory tests
The workup should include a complete blood count (CBC), which will likely reveal leukocytosis and possibly anemia. Furthermore, analysis of liver function tests (LFTs) in acute illness will reflect elevated aspartate aminotransferase (AST) levels while cases of chronic liver abscess are associated with normal AST levels and increased alkaline phosphatase. The latter is typically high in most cases.
Diagnostic tests
Since most individuals with amebic liver abscess do not have coexistent intestinal amebiasis, only a small percentage will have detectable cysts in stool [5] [7]. Hence, stool analysis is not typically useful. Among the various stool studies, antigen or DNA detection of E. histolytica is the preferred diagnostic technique [5].
Serologic studies, which are commonly used to diagnose an amebic liver abscess, yield positive results despite a discrepancy with negative stool tests [8]. The enzyme immunoassay (EIA) test is sensitive, rapid and inexpensive [9]. Also, an amebic liver abscess can be diagnosed through the detection of the E. histolytica galactose lectin antigen using enzyme-linked immunosorbent assay (ELISA). This method is sensitive and rapid [1]. Additionally, there are antibody and antigen point-of-care tests currently under investigation [10].
Imaging
A liver abscess can be detected by various imaging modalities although they do not identify the etiology (amebic versus pyogenic ) [5]. Abdominal ultrasonography, the recommended initial study, demonstrates a sensitivity of 75% to 90% and differentiates an abscess from solid lesions such as tumors. Computed tomography (CT) scan is associated with an up to 95% sensitivity and contrast-enhancement helps distinguish an abscess from a tumor. Magnetic resonance imaging (MRI), like CT, is sensitive but not specific for the diagnosis of an abscess.
Other
Percutaneous needle aspiration of the hepatic abscess can be performed if needed [11].