eMedicine Specialties > Infectious Diseases > Parasitic Infections

Acanthamoeba: Differential Diagnoses & Workup

Author: Nancy F Crum-Cianflone, MD, Consulting Staff, Department of Internal Medicine, Division of Infectious Diseases, Naval Medical Center at San Diego; HIV Research Physician, Infectious Disease Clinical Research Program, Uniformed Services University of the Health Sciences
Contributor Information and Disclosures

Updated: Jun 30, 2008

Differential Diagnoses

Coccidioidomycosis (Infectious Diseases)
Toxoplasmosis
Cryptococcosis
Tuberculosis
Herpes Simplex
Herpes Zoster
Histoplasmosis

Other Problems to Be Considered

Keratitis
Bacterial keratitis
Viral (herpes, varicella) keratitis
Fungal keratitis

GAE
Naegleria, Balamuthia infections
Epilepsy
Brain tumor or CNS lymphoma
Numerous other causes of aseptic meningitis or encephalitis

Workup

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.
    • 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.3
    • 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 diagnosed postmortem or via brain biopsy.
    • 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.
  • Disseminated disease: Perform biopsy and culture areas of involvement.

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.

Procedures

  • Keratitis: Obtain eye scrapings or biopsy samples.
  • 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).

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.

More on Acanthamoeba

Overview: Acanthamoeba
Differential Diagnoses & Workup: Acanthamoeba
Treatment & Medication: Acanthamoeba
Follow-up: Acanthamoeba
References
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References

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  2. Wilhelmus KR, Jones DB, Matoba AY, et al. Bilateral acanthamoeba keratitis. Am J Ophthalmol. Feb 2008;145(2):193-197. [Medline].

  3. Parmar DN, Awwad ST, Petroll WM, et al. Tandem scanning confocal corneal microscopy in the diagnosis of suspected acanthamoeba keratitis. Ophthalmology. Apr 2006;113(4):538-47. [Medline].

  4. Rabinovitch T, Weissman SS, Ostler HB, et al. Acanthamoeba keratitis: clinical signs and analysis of outcome. Rev Infect Dis. Mar-Apr 1991;13 Suppl 5:S427. [Medline].

  5. Park DH, Palay DA, Daya SM, et al. The role of topical corticosteroids in the management of Acanthamoeba keratitis. Cornea. May 1997;16(3):277-83. [Medline].

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Further Reading

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Keywords

Acanthamoeba, Acanthamoeba castellanii, A castellanii, Acanthamoeba polyphaga, A polyphaga, Acanthamoeba culbertsoni, A culbertsoni, Acanthamoeba palestinensis, A palestinensis, Acanthamoeba astronyxis, A astronyxis, Acanthamoeba hatchetti, A hatchetti, Acanthamoeba rhysodes, A rhysodes, Acanthamoeba divionensis, A divionensis, Acanthamoeba quna, A quna, Acanthamoeba lugdunensis, A lugdunensis, Acanthamoeba griffini, A griffini,Naegleria, Balamuthia, acanthamebic infection, keratitis in contact lens wearers, granulomatous amebic encephalitis, GAE, disseminated disease, free-living amoebas, disseminated granulomatous amebic disease, amebic keratitis, Acanthamoeba keratitis

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Contributor Information and Disclosures

Author

Nancy F Crum-Cianflone, MD, Consulting Staff, Department of Internal Medicine, Division of Infectious Diseases, Naval Medical Center at San Diego; HIV Research Physician, Infectious Disease Clinical Research Program, Uniformed Services University of the Health Sciences
Nancy F Crum-Cianflone, MD is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Medical Editor

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: Gilead Sciences Salary Management position

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

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, and Massachusetts Medical Society
Disclosure: Nothing to disclose.

CME Editor

Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital
Eleftherios Mylonakis, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Society for Microbiology, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

Chief Editor

Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital
Burke A Cunha, MD is a member of the following medical societies: American College of Chest Physicians, American College of Physicians, and Infectious Diseases Society of America
Disclosure: Nothing to disclose.

 
 
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