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Updated: Feb 23 2022

Amebic Liver Abscess

  • Snaphot
    • 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
    • Associated conditions
      • amebic colitis
      • ameboma
      • pleuropulmonary infection
      • cardiac infection
      • brain abscess
      • cutaneous infection
  • 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
  • Presentation
    • Symptoms
      • RUQ pain
      • cough
      • sweating
      • malaise
      • weight loss
      • anorexia
      • hiccup
      • diarrhea
    • Physical exam
      • fever
      • jaundice
      • hepatomegaly
      • RUQ tenderness
  • 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
    • Diagnostic testing
      • diagnostic approach
        • diagnosis is primarily based on clinical presentation and confirmed via serologic or antigenic testing
      • 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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