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Key Features

Essentials of Diagnosis

  • Acute meningoencephalitis or chronic granulomatous encephalitis after contact with warm fresh water

  • Keratitis, particularly in contact lens users

General Considerations

  • Free-living amoebas of the genus Acanthamoeba, Naegleria, Balamuthia, and Sappinia

  • Found in soil and in fresh, brackish water

Granulomatous amebic encephalitis

  • Caused by Acanthamoeba species, Balamuthia mandrillaris, and Sappinia

  • More chronic than primary amebic meningoencephalitis (see Amebic Meningoencephalitis, Primary)

  • Neurologic disease

    • May be preceded by skin lesions, including ulcers and nodules

    • Develops slowly after an uncertain incubation period


  • Painful, sight-threatening corneal infection

  • Associated with corneal trauma, most commonly after use of contact lenses and contaminated saline solution

Clinical Findings

Symptoms and Signs

Granulomatous amebic encephalitis

  • Headache

  • Meningismus

  • Nausea, vomiting

  • Lethargy

  • Low-grade fevers

  • Focal neurologic findings, mental status abnormalities


  • Progresses slowly, with waxing and waning clinical findings over months

  • Severe eye pain

  • Photophobia

  • Tearing

  • Blurred vision

Differential Diagnosis

  • Many cases of Acanthamoeba keratitis are misdiagnosed as viral keratitis


Laboratory Tests

Granulomatous amebic encephalitis

  • Cerebrospinal fluid

    • Shows lymphocytic pleocytosis with elevated protein levels

    • Amoebas not typically seen

  • Diagnosis can be made by biopsy of skin or brain lesions

  • Lumbar puncture is dangerous due to increased intracranial pressure


  • Lack of response to antibacterial, antifungal, and antiviral topical treatments and potential use of contaminated contact lens solution are suggestive of the diagnosis

  • Ocular examination shows corneal ring infiltrates, but these can also be caused by other pathogens

  • Diagnosis can be made by examination or culture of corneal scrapings

  • Available diagnostic techniques include

    • Examination of a wet preparation for cysts and motile trophozoites

    • Examination of stained specimens

    • Evaluation with immunofluorescent reagents, culture of organisms, and polymerase chain reaction

Imaging Studies

  • CT and MRI show single or multiple nonspecific lesions in patients with encephalitis



Granulomatous amebic encephalitis

  • Some patients have been treated successfully with various combinations of

    • Flucytosine

    • Pentamidine

    • Fluconazole or itraconazole

    • Sulfadiazine

    • Trimethoprim-sulfamethoxazole

    • Azithromycin

  • However, no treatment has been proved effective


  • Can be cured with local therapy

  • Topical propamidine isethionate (0.1%), chlorhexidine digluconate (0.02%), polyhexamethylene biguanide, neomycin-polymyxin B-gramicidin, miconazole, and combinations of these agents have been used successfully

  • Oral itraconazole or ketoconazole can be ...

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