A 24-year-old man comes to the emergency department due to bloody diarrhea. The patient's symptoms began 10 days ago with episodic abdominal discomfort and loose stools. The symptoms have progressively worsened, and he has had 6-8 stools mixed with blood and mucus over the past 2 days. The patient recently returned from a 2-week trip to Egypt and felt well while traveling. Temperature is 38 C (100.4 F), blood pressure is 120/70 mm Hg, and pulse is 86/min. The abdomen is soft with mild tenderness on palpation of lower quadrants. There is no guarding or rebound tenderness, and bowel sounds are hyperactive. Stool testing is negative for Clostridioides difficile toxin, and stool culture yields no bacteria. Sigmoidoscopy with biopsy reveals colonic ulcers with undermining edges that contain trophozoites. The organism responsible for this patient's condition can also cause which of the following extraintestinal manifestations?
Entamoeba histolytica | |
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RUQ = right upper quadrant. | |
Entamoeba histolytica is an amoeba that infects the gastrointestinal tract of humans and is transmitted via the fecal-oral route when cysts are ingested from contaminated food or water. Cases are most common in developing regions where sanitation is poor. Most infected patients have no symptoms, but a minority (~10%) develop clinically significant colitis with subacute bloody, mucoid diarrhea, abdominal pain, and fever. The diagnosis is confirmed when cysts and trophozoites are seen on stool studies and/or colonic biopsy demonstrates flask-shaped ulcers (with trophozoites).
Although most infections stay localized to the colon, a small minority (~1%) disseminate through the bloodstream to the liver, lungs, and/or brain. The most common extraintestinal manifestation is a single amebic liver abscess in the right lobe of the liver. Invasive strains are more likely to have amebic proteases that degrade host extracellular matrix components and secretory IgA. Most invasive strains also demonstrate contact-dependent cytotoxicity, which is facilitated by an amebic lectin that binds to host cells.
(Choice A) Liver flukes (eg, Clonorchis, Opisthorchis) most often occur after a person consumes contaminated fish. The pathogen can remain in the bile duct of an infected person for decades. Many cases are asymptomatic, but complications such as bile duct obstruction can occur.
(Choice B) Ingestion of the pork tapeworm Taenia solium in the egg stage leads to neurocysticercosis, which is characterized by the formation of cystic brain lesions. Manifestations often occur years later and include seizures (primarily) and focal neurologic signs. Spread of E histolytica to the brain would cause an abscess, not a cyst.
(Choice C) Schistosomiasis is an infection caused by parasitic blood flukes acquired from bathing/swimming in water contaminated with infected freshwater snails. Intestinal schistosomiasis (eg, Schistosoma mansoni) can cause colitis, but trophozoites would not be seen on colonic biopsy. Granulomatous cystitis is seen with genitourinary, not intestinal, schistosomiasis (eg, Schistosoma haematobium).
(Choice D) Cutaneous larva migrans is a hookworm infection that causes an intensely itchy, reddish-brown, migrating, serpiginous track in the area near penetration (usually the lower extremities).
(Choice F) Reactive arthritis can develop following gastrointestinal infection with certain bacteria (eg, Salmonella, Shigella, Campylobacter), but stool culture would likely show pathogenic bacteria, and trophozoites would not be seen on biopsy. Reactive arthritis is very uncommon with E histolytica infection.
Educational objective:
Entamoeba histolytica is an amoeba that causes colitis characterized by trophozoites and flask-shaped ulcers on biopsy. It can occasionally (~1%) invade the colonic wall and disseminate through the blood to the liver, brain, or lungs. A single amebic liver abscess is the most common extraintestinal manifestation.