A 48-year-old woman from rural Odisha presents with a 6-week history of fever (38–39°C), right upper quadrant pain, and hepatomegaly (liver edge 4 cm below costal margin). She denies diarrhea. Ultrasound shows a 6 cm hypoechoic lesion in the right lobe of the liver with internal echoes. Serum anti-Entamoeba antibodies are positive. Blood culture is sterile. What is the most likely diagnosis?

## Clinical Diagnosis: Amebic Liver Abscess ### Key Diagnostic Criteria **Key Point:** The combination of fever, RUQ pain, hepatomegaly, positive serology, and sterile blood culture in an endemic area is diagnostic of amebic liver abscess. **High-Yield:** Amebic liver abscess occurs in only 5–10% of infected individuals but is a major extraintestinal complication. It can develop even without a history of dysentery. ### Clinical Features of Amebic Liver Abscess | Feature | Amebic Abscess | Pyogenic Abscess | Echinococcal Cyst | TB Hepatitis | |---------|----------------|------------------|-------------------|-------------| | **Onset** | Subacute (weeks) | Acute (days) | Insidious (months–years) | Chronic (weeks–months) | | **Fever pattern** | Low-grade, persistent | High, spiking | Absent or low-grade | Low-grade, evening rise | | **Blood culture** | Sterile (100%) | Positive (50–80%) | Sterile | Sterile | | **Serology** | Positive (>90%) | Negative | Negative | Negative | | **Ultrasound** | Hypoechoic, homogeneous or internal echoes | Septated, debris | Daughter cysts, calcification | Hypoechoic nodules | | **Aspiration fluid** | Anchovy paste (sterile) | Purulent | Clear, serous | Caseous | | **Location** | Right lobe (80%) | Multiple, scattered | Single or multiple | Diffuse | ### Why Amebic Abscess Is Most Likely 1. **Positive serology**: Anti-Entamoeba antibodies are positive in >90% of patients with amebic liver abscess. This is the gold standard for diagnosis. 2. **Sterile blood culture**: Amebic abscesses are sterile because the abscess contains trophozoites and necrotic liver tissue, not bacteria. Pyogenic abscesses typically yield positive cultures. 3. **Subacute presentation**: 6-week fever with RUQ pain and hepatomegaly is classic for amebic abscess. Pyogenic abscess presents more acutely with high spiking fever. 4. **Ultrasound findings**: A 6 cm hypoechoic lesion with internal echoes is consistent with amebic abscess. The "anchovy paste" appearance (sterile, chocolate-colored fluid) is characteristic. 5. **No diarrhea history**: Amebic liver abscess can occur without preceding dysentery in up to 30% of cases, especially if the primary colitis was mild or asymptomatic. **Clinical Pearl:** The absence of diarrhea does NOT exclude amebic liver abscess. Many patients present with isolated hepatic disease; the abscess develops from hematogenous spread during the early invasive phase. ### Pathophysiology: From Colitis to Liver Abscess ```mermaid flowchart TD A[E. histolytica trophozoites invade colon]:::outcome --> B[Mucosal ulceration] B --> C[Trophozoites enter portal venules] C --> D[Hematogenous spread to liver]:::action D --> E{Immune response adequate?}:::decision E -->|Yes| F[Abscess walled off]:::outcome E -->|No| G[Abscess enlarges] G --> H{Rupture risk?}:::decision H -->|No| I[Contained abscess, fever, RUQ pain]:::action H -->|Yes| J[Peritonitis, sepsis]:::urgent I --> K[Positive serology by day 7-10]:::outcome ``` **Mnemonic:** **SHEAR** — Serology positive, Hepatomegaly, Endemic area, Anchovy paste fluid, RUQ pain ### Diagnostic Approach 1. **Serology**: Positive in >90% of amebic liver abscess (gold standard). 2. **Imaging**: Ultrasound or CT shows hypoechoic lesion; MRI shows characteristic appearance. 3. **Aspiration**: Only if diagnosis uncertain or therapeutic drainage needed. Fluid is sterile, acellular, chocolate-colored (no trophozoites visible in aspirate). 4. **Stool microscopy**: May be negative even with liver abscess (50% of cases have no intestinal involvement). [cite:Robbins 10e Ch 8; Harrison 21e Ch 229]