JOURNAL OF THE LOUISIANA STATE MEDICAL SOCIETY
discharged on a ten-day course of metronidazole and a seven- day course of paromomycin. Prior to discharge, a serum sample was sent to a reference lab for amoebic serology studies. Several weeks later, serologic testing came back positive for anti- amoebic antibodies.
into a larger cyst. 2,7 Symptoms of an amoebic liver abscess (ALA) include right upper quadrant tenderness, generalizedabdominal pain, fever, and weakness. 14 The time from the development of an ALA to clinical presentation can vary from as soon as a week to more than a month. Similar to our patient, individuals with an ALA will frequently admit to a distant history of abdominal pain and diarrhea that later resolved. 13 " It is estimated that 40-50 million people are infected annually with Entamoeba species, and that there are 40,000-100,000 deaths annually due to these infections. "
DISCUSSION
Epidemiology, Pathophysiology, and Clinical Presentation
The genus Entamoeba contains numerous species, three of which, E. histolytica , E. dispar , and E. moshkovskii , can be pathogenic in the human colon. 1 It is estimated that 40-50 million people are infected annually with Entamoeba species, and that there are 40,000-100,000 deaths annually due to these infections. 2 Most Entamoeba infections are due to E. dispar , followed by E. histolytica and E. moshkovskii . E. dispar infection was believed to be non-pathogenic; however, it is now known to be pathogenic, albeit less frequently than E. moshkovskii and E. histolytica. 3-6 Both E. moshkovskii and E. histolytica are capable of invading the colonic mucosa and extra-colonic organs, particularly the liver. Until recently, E. dispar was believed to only colonize the colon, however, extra-colonic organ involvement, including the liver, has been reported. 3,7 Entamoeba species are endemic in most parts of the developing world. In industrialized countries, most cases occur in immigrants or in individuals who have traveled to endemic areas, although men who have sex with men and institutionalized individuals are also at an increased risk of infection. Infected individuals will pass E. histolytica cysts in their feces, which, if ingested in contaminated food or water, can cause infection in other hosts. 2,7 Once ingested, trophocytes will undergo excystation in the ileum and will migrate into and attach to the colonic mucosa. 2 The excystation and migration process can take days to years to occur. 7 Approximately 90% of individuals with E. histolytica will have asymptomatic infections, while 10% will develop amoebic colitis. The colitis, due to penetration of the colonic mucosa by trophocytes, may be self-limited and manifest as abdominal pain, fever, and diarrhea with possible hematochezia. 7 Although uncommon, patients with ameobic colitis can also develop more severe complications, such as fulminant colitis or bowel perforations. Bowel strictures are also an uncommon long-term complication. 6,7 Given the high rates of asymptomatic infection, there is ongoing research to identify the genetic hallmarks associated with virulent strains of E. histolytica . 8 Patients with ameobic colitis may also develop disseminated amoebic infections; the most common extra-colonic site is the liver, although the lungs, brain, and skin can also be infected. 7,9-12 It is estimated that less than 1% of individuals infected with E. histolytica infection will develop liver involvement. Typically amoebic colitis occurs in the ascending colon, and since the superior mesenteric vein drains into the right hepatic lobe, most cases of invasive E. histolytica will involve this region of the liver. 13 Due to inflammation and ultimately destruction of hepatocytes, the invasive amoebas will cause small cysts that amalgamate
Diagnosis and treatment
Patients with an ALA will classically present with right upper quadrant pain, and will have a history of living or traveling to a developing country. Additionally, if large enough, ALA can cause jaundice due to biliary obstruction, as well as inferior vena cava obstruction secondary to external compression by an abscess. 13 On laboratory testing, patients will often have mild leukocytosis without eosinophilia, as well as elevated c-reactive protein and/ or erythrocyte sedimentation rates. 13,14 Broadly, there are two types of ALA: acute (patients who present with less than ten days of symptoms) or chronic (patients who present with greater than twoweeks of symptoms). Patients with acute abscesses tend to present with fevers, chills, and a severely tender liver and abdomen, whereas patients with chronic ALA tend to have a protracted course of less severe abdominal pain. Patients with acute ALA will often have a normal alkaline phosphatase with an elevate AST, while patients with chronic ALA will have an abnormal alkaline phosphatase with a normal AST level. Both acute and chronic abscesses respond well to treatment, but acute abscesses aremore prone to complications, such as cyst rupture or suprainfection. 13 Although imaging modalities can identify hepatic abscesses, they are often unable to distinguish ALA from other infections, such as Mycobaceterium tuberculosis, a hydatid cyst, or bacterial cysts secondary to ascending cholangitis. 13 Most hepatic abscesses can be identified by ultrasound, which, for an ALA, will show a homogeneous hypoechoic oval lesion. If further imaging is need, a computerized tomography (CT) scan or magnetic resonance imaging (MRI) can be used. 6,13 Since ALA, unlike pyogenic abscesses, contain few leukocytes, a 99mTc scan can be used to distinguish the two. Using this modality, an ALA will appear as a “cold” lesion with a “hot” rim, while an entire pyogenic abscess will be “hot.” 13
J La State Med Soc VOL 169 JULY/AUGUST 2017 107
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