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 ETIOLOGY 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