Acanthamoeba Infection Workup

Updated: Aug 14, 2017
  • Author: David R Haburchak, MD, FACP; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Workup

Laboratory Studies

Acanthamoeba keratitis

Diagnosis requires a high index of suspicion; an early diagnosis is critical for the retention of good visual acuity. The earliest clue to this infection is a dendriform pattern noted on the epithelium of the cornea.

Acanthamoeba trophozoites or cysts can be demonstrated with corneal scrapings or a biopsy sample via wet mount, stains, histopathologic examination, or culture.

Motile trophozoites may be seen in a wet-mount preparation.

Stain corneal scrapings with calcofluor white (stains cyst walls) and examine specimen with fluorescent microscopy. [22]

Cysts and trophozoites can be seen with a number of stains, including hematoxylin and eosin (H&E), Giemsa, and Wright.

Amoebae may be cultured on a buffered charcoal yeast extract or with a non-nutrient agar (NNA) overlaid with organisms such as Escherichia coli.

Conduct polymerase chain reaction (PCR) of biopsy specimens, if available (see below).

In addition, the use of tandem scanning confocal corneal microscopy has been described as a noninvasive method for diagnosis. [23]

If corneal specimens are unremarkable, consider culturing the contact lenses and saline solution for Acanthamoeba.

Suprainfecting bacteria can complicate the diagnosis; isolation of a bacterial pathogen does not exclude Acanthamoeba as the cause of the keratitis.

Acanthamoeba granulomatous amebic encephalitis (GAE)

This condition is best diagnosed via brain biopsy. Sometimes cases are not recognized until postmortem evaluation.

Cerebrospinal fluid examination reveals an increased number of white blood cells (up to 800 cells/µL, primarily lymphocytes), elevated protein levels, and decreased glucose levels.

Examining the CSF for organisms is of very low yield.

Serologic studies are not useful.

Disseminated Acanthamoeba disease

Perform biopsy and culture areas of involvement.

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Imaging Studies

Acanthamoeba granulomatous amebic encephalitis (GAE)

CT scan should be obtained before a lumbar puncture is performed to ensure that this procedure is not contraindicated because of the herniation risk.

Findings on CT scan include multiple nonenhancing lesions in the cerebral cortex.

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Procedures

Acanthamoeba keratitis

Obtain eye scrapings or biopsy samples. Corneal scrapping can be examined via a wet mount for motile trophozoites.

Acanthamoeba granulomatous amebic encephalitis (GAE)

Perform lumbar puncture and brain biopsy.

Lumbar puncture may be contraindicated if signs of increased intracranial pressure are present.

If skin lesions are present, perform skin biopsy.

Disseminated Acanthamoeba disease

Obtain biopsy samples of the involved sites (eg, skin, sinuses).

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Histologic Findings

In keratitis, amebic cysts and trophozoites are found within the cornea. An acute or mixed inflammatory infiltrate may contain giant cells. Corneal revascularization may occur.

Individuals with GAE have moderate-to-severe cerebral edema. Necrotizing granulomas that contain perivascular trophozoites and cysts are usually located in the cerebellum, mid brain, and brain stem. Multinucleated giant cells may be present within the granulomas. Granulomas are usually noted among immunocompetent patients. On biopsy specimens, angiitis with perivascular cuffing with lymphocytes may be seen. The leptomeninges are spared except when they directly overlie areas of cortical involvement.

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Other Tests

Based on animal models, polymerase chain reaction (PCR) testing appears to be a promising method of rapid keratitis diagnosis. [24]

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