Differential Diagnosis: Amebiasis
  • Overview:-intestinal amebiasis
    • Consider other infectious/noninfectious diarrhea causes and gastrointestinal disease in immigrants/travelers from endemic areas
  • Intestinal Amebiasis:
    • Diagnostic key: stool examination {routine lab tests: not useful}
    • Difficulties in performing correct stool examinations
      • Common false-positives & false-negatives
        • False Negatives caused by:
          • antimicrobial agents
          • soap/tap water enemas (lyse trophozoites)
          • particular to matter (barium or bismuth)-obscures organisms
        • False Positives caused by:
          • leukocytes misread as amebas
          • other amebas confused with E. histolytica
      • Should take multiple stool samples (one "negative" stool result is not sufficient to rule out intestinal amebiasis)
      • Samples must be properly maintained if not analyzed immediately
    • Presence of many fecal leukocytes suggests some other diagnosis since E. histolytica causes lysis of neutrophils
      • amebiasis differentiation from bacterial diarrheal disease, e.g.shigellosis
    • Indirect hemagglutination test: 70% sensitivity in patients with active intestinal disease-- only 10% sensitivity in asymptomatic cyst carrier
  • Overview:Extraintestinal Amebiasis:-
    • Differential includes:
      1. pyrogenic abscess
        • usually multiple abscesses
        • associated with biliary tract disease or other intraabdominal disease
      2. metastatic/primary tumor (includes hemangioma)
    • Typical amebic abscess:
      • single
      • right lobe
  • Extraintestinal Amebiasis:
    • Serology helpful if patient not from an endemic area
    • Diagnosis made based on:
      1. epidemiological information
      2. radiographic findings
        • ultrasonography-most cost-effective; slightly less sensitive than other techniques
        • MRI
        • CT
        • radioisotope liver scans
      3. positive serology
        • most sensitive: indirect hemagglutination (95 percent sensitivity in extraintestinal disease) -- does not differentiate present from past infection
Primary Reference: Morgan, Juliette and del Rio, Carlos, Amebiasis in Medicine for the Practicing Physician (Hurst, J. W., ed) Appleton-Lange, 1996, pp. 457-459.