A 28-year-old woman from Kolkata presents with a 2-month history of right upper quadrant pain, fever (38.5°C), and hepatomegaly. Ultrasound shows a 6 cm hypoechoic lesion in the right lobe of the liver with a thickened wall. Stool microscopy is negative for parasites. Serology is strongly positive for anti-Entamoeba histolytica IgG antibodies. Aspiration of the abscess yields 'anchovy paste' material. What is the most likely diagnosis and the preferred initial antimicrobial agent?

Explanation

## Amoebic Liver Abscess: Diagnosis and Management ### Clinical Presentation and Diagnosis **Key Point:** Amoebic liver abscess (ALA) is the most common extraintestinal manifestation of E. histolytica. The classic triad is RUQ pain, fever, and hepatomegaly in a patient from an endemic area with positive serology. ### Diagnostic Features | Feature | Amoebic Liver Abscess | Pyogenic Abscess | Echinococcal Cyst | |---------|----------------------|------------------|-------------------| | **Serology** | Positive IgG (>90%) | Negative | Negative | | **Stool** | May be negative | N/A | N/A | | **Aspirate** | 'Anchovy paste' (sterile) | Purulent, culture+ | Clear fluid | | **Ultrasound** | Hypoechoic, round | Heterogeneous | Cystic with septa | | **Fever pattern** | Mild to moderate | High spiking | Absent | | **Epidemiology** | Endemic areas (India) | Biliary/GI source | Sheep-herding regions | **High-Yield:** The "anchovy paste" appearance is pathognomonic for amoebic abscess. It is sterile (no bacterial growth) because the material is necrotic liver tissue, not pus. ### Pathophysiology of ALA ```mermaid flowchart TD A[E. histolytica trophozoites<br/>invade intestinal mucosa]:::outcome --> B[Portal bacteremia<br/>to liver]:::action B --> C[Trophozoites lodge in<br/>hepatic sinusoids]:::action C --> D[Release cytolytic enzymes<br/>destroy hepatocytes]:::action D --> E[Liquefactive necrosis<br/>forms abscess cavity]:::action E --> F[Anchovy paste material<br/>Sterile, acellular]:::outcome F --> G[RUQ pain + fever<br/>+ hepatomegaly]:::outcome ``` ### Management of ALA **Clinical Pearl:** Unlike intestinal amoebiasis, ALA does NOT require luminal amoebicide if the patient has no diarrhea or stool cysts. However, if dysentery coexists, add paromomycin after metronidazole. **Mnemonic:** **METRO-CHLORO** for ALA = Metronidazole + Chloroquine (if severe or multiple abscesses) #### First-Line Therapy 1. **Metronidazole 750 mg TDS for 7–10 days** — tissue amoebicide, excellent hepatic penetration 2. **Chloroquine 600 mg base daily for 2 weeks** — concentrates in liver, synergistic with metronidazole (used in severe/multiple abscesses or if metronidazole alone fails) #### Aspiration Indications - Large abscess (>5 cm) with risk of rupture - Failure to improve after 72 hours of medical therapy - Diagnostic uncertainty - Left lobe abscess (risk of pericardial rupture) **Tip:** Aspiration is therapeutic AND diagnostic — it relieves pressure and confirms the diagnosis (sterile, acellular material). Culture is negative, distinguishing ALA from pyogenic abscess. ### Why Serology is Critical - Positive in >90% of ALA cases - Negative in asymptomatic cyst carriers - IgG indicates tissue invasion; IgM indicates acute infection - Stool may be negative in ALA (no intestinal involvement in ~10% of cases) [cite:Harrison 21e Ch 237; Park 26e Ch 9]