eMedicine Specialties > Pediatrics: General Medicine > Parasitology

Amebic Meningoencephalitis: Differential Diagnoses & Workup

Author: Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Contributor Information and Disclosures

Updated: Jan 21, 2009

Differential Diagnoses

Amebiasis
Mixed Connective Tissue Disease
Astrocytoma
Mucormycosis
Catscratch Disease
Neurocysticercosis
Coccidioidomycosis
Periventricular Hemorrhage-Intraventricular Hemorrhage
Craniopharyngioma
Polyarteritis Nodosa
Echinococcosis
Rabies
Gnathostomiasis
Taenia Infection
Histoplasmosis
Toxoplasmosis
Malaria
Tuberculosis
Medulloblastoma
Vasculitis and Thrombophlebitis
Meningitis, Aseptic
Meningitis, Bacterial
Meningococcal Infections

Other Problems to Be Considered

Angiostrongylus cantonensis
Baylisascaris procyonis
Brain abscess
Cryptococcosis
Cysticercus cellulosae
Encephalitis
Intracranial hemorrhage
Sappinia diploidea

Workup

Laboratory Studies

  • Primary amebic meningoencephalitis (PAM): Lumbar puncture for cerebrospinal fluid (CSF) analysis is the primary diagnostic tool.
    • CSF analysis is indistinguishable from that in acute bacterial meningitis, except that Gram stain findings are always negative.
    • A predominance of neutrophils is observed, with elevated protein levels, decreased glucose levels, and RBCs present.
    • If PAM is suspected, light microscopy with phase contrast on fresh, still-warm CSF may reveal motile trophozoites.
    • Recently, a triplex real-time polymerase chain reaction (PCR) assay for Naegleria, Acanthamoeba, and Balamuthia has been developed by the Centers for Disease Control and Prevention (CDC).5
  • Granulomatous amebic encephalitis (GAE): Lumbar puncture for CSF analysis is the primary diagnostic tool.
    • CSF analysis typically demonstrates less inflammation than that observed in individuals with PAM.
    • Opening pressure is elevated.
    • CSF analysis mimics that of aseptic meningitis, with low-to-moderate, primarily mononuclear WBCs; elevated protein levels; and, often, near-normal or slightly decreased glucose levels.
    • No trophozoites appear in the CSF.
    • Recently, a triplex real-time PCR assay for Naegleria, Acanthamoeba, and Balamuthia has been developed by the CDC.5

Imaging Studies

  • CT or MRI
    • Head CT scanning or MRI should precede lumbar puncture if evidence of focal CNS involvement or elevated intracranial pressure (ICP) is present.
    • CT and MRI frequently reveal meningeal hyperemia and cerebral edema.
    • Imaging studies may reveal evidence of increased ICP or cerebral herniation.
    • In an individual with PAM, the olfactory bulbs, temporal lobes, and frontal lobes are involved; however, disease may be diffuse.
  • In individuals with GAE, focal lesions are very common and may be found throughout the CNS.

Procedures

  • A biopsy of focal granulomatous lesions in persons with GAE may assist in making the diagnosis.

Histologic Findings

  • Biopsies or postmortem specimens from persons with PAM reveal the intense inflammation with invasion of polymorphonuclear leukocytes, hemorrhage, and necrosis typical of acute meningitis.
  • Fluorescent antibodies may help to identify the numerous trophozoites present.
  • In individuals with GAE, moderate granulomatous inflammation with prominent vascular involvement is typically present.
  • Both trophozoites and cysts, which are less numerous, can be identified through the use of fluorescent antibodies.
  • Recently, tissue-based PCR has been proposed as a diagnostic aid.5

More on Amebic Meningoencephalitis

Overview: Amebic Meningoencephalitis
Differential Diagnoses & Workup: Amebic Meningoencephalitis
Treatment & Medication: Amebic Meningoencephalitis
Follow-up: Amebic Meningoencephalitis
References
Further Reading
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Further Reading

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Keywords

amebic meningoencephalitis, acanthamebic keratoconjunctivitis, Acanthamoeba, aphasia, aseptic meningitis, ataxia, bacterial meningitis, Balamuthia mandrillaris, central nervous system infection, CNS infection, cerebral herniation, cranial nerve palsies, diplopia, encephalitis, Entamoeba histolytica, granulomatous amebic encephalitis, GAE, hemiplegias, intracranial pressure, ICP, leptomyxid meningitis, meningitis, myocarditis, Naegleria fowleri, photophobia, primary amebic meningoencephalitis, PAM, Sappinia diploidea

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Contributor Information and Disclosures

Author

Robert W Tolan Jr, MD, Chief, Division of Allergy, Immunology and Infectious Diseases, The Children's Hospital at Saint Peter's University Hospital; Clinical Associate Professor of Pediatrics, Drexel University College of Medicine
Robert W Tolan Jr, MD is a member of the following medical societies: American Academy of Pediatrics, American Medical Association, American Society for Microbiology, American Society of Tropical Medicine and Hygiene, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, Phi Beta Kappa, and Physicians for Social Responsibility
Disclosure: GlaxoSmithKline Honoraria Speaking and teaching; MedImmune Honoraria Consulting; MedImmune Honoraria Speaking and teaching; Merck Honoraria Speaking and teaching; Novartis Honoraria Speaking and teaching; sanofi pasteur Grant/research funds Unrestricted research grant; sanofi pasteur  Consulting; sanofi pasteur Honoraria Speaking and teaching; Tap Honoraria Speaking and teaching; Baxter Healthcare Honoraria Speaking and teaching

Medical Editor

Michael D Nissen, MBBS, BMedSc, FRACP, FRCPA, Associate Professor in Biomolecular, Biomedical Science & Health, Griffith University; Director of Infectious Diseases and Unit Head of Queensland Paediatric Infectious Laboratory, Sir Albert Sakzewski Viral Research Centre, Royal Children's Hospital
Michael D Nissen, MBBS, BMedSc, FRACP, FRCPA is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Pediatric Infectious Diseases Society, Royal Australasian College of Physicians, and Royal College of Pathologists of Australasia
Disclosure: Nothing to disclose.

Pharmacy Editor

Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine
Disclosure: Pfizer Inc Stock Investment from financial planner; Avanir Pharma Stock Investment from financial planner ; WebMD Salary and stock Employment and investment from financial planner

Managing Editor

Martin Weisse, MD, Program Director, Associate Professor, Department of Pediatrics, West Virginia University
Martin Weisse, MD is a member of the following medical societies: Ambulatory Pediatric Association, American Academy of Pediatrics, and Pediatric Infectious Diseases Society
Disclosure: Nothing to disclose.

CME Editor

David Pallares, MD, Clinical Assistant Professor, Department of Pediatrics, Division of Allergy and Immunology, University of Louisville
David Pallares, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology
Disclosure: Nothing to disclose.

Chief Editor

Russell W Steele, MD, Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine
Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association
Disclosure: None None None

 
 
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