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Acanthamoeba Workup

  • Author: Nancy F Crum-Cianflone, MD, MPH; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
 
Updated: Nov 30, 2015
 

Laboratory Studies

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.[8]

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.

In addition, the use of tandem scanning confocal corneal microscopy has been described as a noninvasive method for diagnosis.[9]

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.

Granulomatous amebic encephalitis

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 disease

Perform biopsy and culture areas of involvement.

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Imaging Studies

Granulomatous amebic encephalitis

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

Keratitis

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

Granulomatous amebic encephalitis

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 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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Contributor Information and Disclosures
Author

Nancy F Crum-Cianflone, MD, MPH Consulting Staff, Department of Internal Medicine, Division of Infectious Diseases, Naval Medical Center at San Diego

Nancy F Crum-Cianflone, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Richard B Brown, MD, FACP Chief, Division of Infectious Diseases, Baystate Medical Center; Professor, Department of Internal Medicine, Tufts University School of Medicine

Richard B Brown, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians, American College of Physicians, American Medical Association, American Society for Microbiology, Infectious Diseases Society of America, Massachusetts Medical Society

Disclosure: Nothing to disclose.

Chief Editor

Pranatharthi Haran Chandrasekar, MBBS, MD Professor, Chief of Infectious Disease, Program Director of Infectious Disease Fellowship, Department of Internal Medicine, Wayne State University School of Medicine

Pranatharthi Haran Chandrasekar, MBBS, MD is a member of the following medical societies: American College of Physicians, American Society for Microbiology, International Immunocompromised Host Society, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Additional Contributors

David Hall Shepp, MD Program Director, Fellowship in Infectious Diseases, Department of Medicine, North Shore University Hospital; Associate Professor, New York University School of Medicine

David Hall Shepp, MD is a member of the following medical societies: Infectious Diseases Society of America

Disclosure: Received salary from Gilead Sciences for management position.

Acknowledgements

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous coauthor William B. Harley, MD, to the development and writing of this article.

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