Question
Extra intestinal amoebiasis
Answer
Extraintestinal amoebiasis refers to disease caused by Entamoeba histolytica spreading beyond the intestinal lumen to distant organs, most commonly the liver, following invasion of the intestinal mucosa and haematogenous spread via the portal circulation.
Amoebic liver abscess — the most common and clinically important form of extraintestinal amoebiasis:
- Pathogenesis: trophozoites invading the colonic mucosa enter the portal venous circulation and are carried to the liver, where they cause focal tissue necrosis and abscess formation — classically described as containing “anchovy paste”-like necrotic material (reddish-brown, sterile pus without significant neutrophilic component, since amoebic necrosis is due to direct cytolytic activity rather than a typical bacterial pyogenic response).
- Clinical features: fever, right upper quadrant pain, tender hepatomegaly; a history of preceding or concurrent dysentery is present in only a minority of cases (many patients have no antecedent diarrhoeal history), an important point to remember.
- Laboratory diagnosis: imaging (ultrasound/CT) showing a well-defined hypoechoic/hypodense lesion, typically in the right lobe; serology (amoebic antibody, e.g., indirect haemagglutination or ELISA) — highly sensitive and the mainstay of diagnosis, since stool examination is often negative in extraintestinal disease (the trophozoites causing the abscess have already left the gut); aspiration of abscess fluid (if performed, usually for diagnostic uncertainty or large/threatening abscesses) shows the characteristic anchovy-paste material, though trophozoites are often not seen on direct examination of the fluid (found more reliably at the abscess wall/margin than the central necrotic material).
Other extraintestinal sites (less common): amoebic involvement of the lung (usually by direct extension from a ruptured liver abscess), brain (rare, but serious), and skin (perianal ulceration from direct extension).
Treatment: metronidazole (tissue amoebicide) followed by a luminal agent (e.g., paromomycin) to eliminate any residual intestinal cyst carriage and prevent relapse/transmission; therapeutic aspiration/drainage for large abscesses or those at risk of rupture, or failing to respond to medical therapy alone.