Updated: 8/7/2019

Amebic Liver Abscess

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  • A 38-year-old man presents to the emergency room for severe upper right quadrant (RUQ) pain for the past week. He describes a dull, 8/10 pain at the RUQ that is worse with breathing. He endorses fever, anorexia, and diaphoresis but denies steatorrhea, nausea/vomit, weight loss, or chest pain. He recently returned from Mexico following a work placement 5 weeks ago. A physical examination demonstrates hepatomegaly and point tenderness at the RUQ.
Introduction
  • Clinical definition
    • type of liver abscess caused by trophozoites of the parasite Entamoeba histolytica  
      • amebic liver abscess is the most common extraintestinal manifestation of amebiasis
    • amebiasis describes disease caused by E. histolytica and often affects the gastrointestinal system
      • most infections are asymptomatic
  • Epidemiology
    • demographics
      • more common in endemic areas which include India, Africa, Mexico, and parts of Central and South America
      • in developed countries, often seen in migrants from and travelers to endemic areas
      • more common among adult men
    • risk factors
      • immunosuppression
      • cancer
      • alcoholism
      • malnutrition
      • recent travel to endemic region
      • steroid use
      • pregnancy
  • Pathogenesis
    • humans are the principal host and reservoir of E. histolytica
    • transmission can occur fecal-orally, person-to-person, or sexually (oral-anal contact) 
      • commonly from consuming food or water that has been contaminated with feces
      • cysts of E. histolytica predominate in formed stools and allows for initial transmission/infection as it is resistant to gastric acid
    • once transmitted, cysts differentiate into its trophozoite form, which feed on bacteria and tissue, reproduce, and colonize the lumen and mucosa of the large intestine 
      • can also spread via the portal circulation to the liver, and rarely the lung, spleen, or brain resulting in metastatic abscesses
    • invasion of the liver most commonly involves the posterior part of the right side
      • abscess results from necrotic hepatocytes and is often described with an “anchovy paste” consistency containing aceullar, proteinaceous debris 
  • Associated conditions
    • amebic colitis
    • ameboma
    • pleuropulmonary infection
    • cardiac infection
    • brain abscess
    • cutaneous infection
Presentation
  • Symptoms 
    • RUQ pain  
    • cough
    • sweating
    • malaise
    • weight loss
    • anorexia
    • hiccup
    • diarrhea
  • Physical exam
    • fever
    • jaundice
    • hepatomegaly
    • RUQ tenderness
Studies
  • Diagnostic testing
    • diagnostic approach
      • diagnosis is primarily based on clinical presentation and confirmed via serologic or antigenic testing
    • imaging
      • ultrasound
        • best initial imaging
        • may demonstrate a cystic intrahepatic cavity with a round, well-defined hypoechoic mass
      • computed tomography (CT) 
        • best initial imaging
        • appears as a low-density mass with peripheral enhancing rim
      • magnetic resonance imaging (MRI)
        • low-signal intensity on T1-weighted images and high-signal intensity on T2-weighted images
    • studies
      • serology and antigen testing
        • confirms acute or previous infection
        • negative serology excludes the disease (though may be negative in the first seven days)
      • abscess aspiration
        • under ultrasound or CT guidance
        • rarely performed but indicated if the cyst appears to be at imminent risk of rupture
        • may visualize trophozoites
      • laboratory studies
        • increased ALP
Differential 
  • Pyogenic liver abscess
    • differentiating factors
      • abscess aspiration will yield bacterial organisms and polymorphonuclear cells
  • Echinococcal disease 
    • differentiating factors
      • will appear different on imaging (e.g., ground-glass appearance)
      • will have negative E. histolytica serology
  • Malignancy 
    • differentiating factors
      • rarely presents with RUQ pain and fever
      • can be differentiated via imaging and tissue biopsy  
Treatment
  • therapy can be initiated empirically based on clinical suspicion pending further diagnostic evaluation
  • First-line 
    • co-current use of a tissue and luminal agent for 7-10 days
    • tissue agents
      • e.g., metronidazole, tinidazole, and nitazoxanide
      • cure rate of > 90%
      • metronidazole is recommended in pregnant patients
    • luminal agents
      • e.g., paromomycin, diiodohydroxyquin, or diloxanide
      • elimination of intraluminal cysts even if stool microscopy is negative
  • Second-line
    • indicated in patients with relapse following therapy or slow response to therapy
    • therapeutic aspiration
    • percutaneous catheter drainage
    • prolonged course of metronidazole
Complications
  • Abscess rupture
  • Peritonitis
  • Hepatic vein or inferior vena cava thrombosis
 

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