Pediatric Naegleria Workup

  • Author: Nicholas John Bennett, MB, BCh, PhD; Chief Editor: Russell W Steele, MD   more...
 
Updated: May 3, 2012
 

Laboratory Studies

  • For practical purposes, N fowleri meningoencephalitis must be rapidly diagnosed. Patients who present with a clinical picture of meningitis (ie, fever, headache, meningismus, nausea and vomiting) should undergo a spinal tap as soon as they present.
  • In patients with PAM, the CSF pressure is often elevated, and the CSF is hemorrhagic. The WBC count can be within the reference range in early infections but rapidly increases to range from 400-26,000 cells/µL with a neutrophilic predominance. The CSF glucose level may be low or within the reference range, but the CSF protein is usually elevated. Results on a Gram stain of the CSF sediment are negative for bacteria. A wet mount must be made because the trophozoites of N fowleri lyse during the heat fixation that precedes the Gram stain. On the wet preparation, motile trophozoites are evident. Care must be taken to avoid confusing N fowleri trophozoites with WBCs and vice versa. In examining CSF for N fowleri, a regular glass slide for a wet mount is preferred to a WBC counting chamber. The regular glass slide allows for better definition of internal structures.
  • The CSF is centrifuged at 150g for 5 minutes. The supernatant is carefully aspirated, and the sediment is gently suspended in the remaining fluid. A drop of this suspension is placed on a slide and covered with a No. 1 coverslip. The slide is observed under a compound microscope using 10 and 40 objectives. Phase contrast optics is preferable. The slide may be warmed to 35°C (to promote amebic movement). The amebae are detected based on their active directional movements. CSF indices in N fowleri include the following:
    • CSF protein levels are elevated.
    • CSF glucose levels are within the reference range or reduced.
    • CSF WBC count is elevated (400-26,000 cells/µL).
    • CSF RBC count is high, and the CSF is often hemorrhagic.
    • CSF Gram stain results are negative for bacteria.
    • CSF wet mount is positive for motile trophozoites and is of paramount importance for the diagnosis.
  • Additional methods of diagnosing N fowleri infection include polymerase chain reaction (PCR), monoclonal antibodies, DNA probes, and isoenzyme profile analysis. However, these methods are more time consuming and labor intensive than routine CSF studies. They are useful in postmortem diagnoses and for research purposes.
  • The CDC can be helpful in working up a possible case of Naegleria infection: http://www.dpd.cdc.gov/dpdx/HTML/Contactus.htm
  • Other nonspecific laboratory findings in peripheral blood include the following:
    • The WBC count is elevated with a neutrophilic predominance.
    • Complete metabolic panel (CMP) may show abnormalities, including hyponatremia associated with acquired diabetes insipidus, hyperglycemia, or both.
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Imaging Studies

  • Limited data are available on imaging studies. One patient has been reported who had a CT scan of the head that demonstrated diffuse enhancement of the gray matter and obliteration of the interpeduncular and quadrigeminal cisterns.
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Other Tests

  • EEG may show signs of reduced cerebral blood flow, including slow and disorganized fundamental rates.
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Procedures

  • The main diagnostic procedure for PAM is to obtain CSF for wet-mount examination for N fowleri, along with standard laboratory examination of the CSF (eg, WBC, RBC, glucose, protein, bacterial and fungal cultures). N fowleri can be cultured on nonnutrient agar plates, which have a lawn of gram-negative bacteria, such as Escherichia coli, covering its surface. "Trails" in the lawn of bacteria that are left by migrating amebae can be visualized following incubation.
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Histologic Findings

  • Amebic trophozoites in perivascular spaces and paraventricular areas
  • Fibrinoid necrosis in some blood vessels
  • Hemorrhage and necrosis
  • Meningeal exudate composed of neutrophils, chronic inflammatory cells, and degenerating amebae
  • Focal demyelination in the white matter of the brain and spinal cord
  • Acute inflammatory reaction in nasal mucous membranes
  • Trophozoites demonstrated on hematoxylin- and eosin-stained slides in involved tissues
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Contributor Information and Disclosures
Author

Nicholas John Bennett, MB, BCh, PhD,  Assistant Professor in Pediatrics, Division of Infectious Diseases, Connecticut Children's Medical Center

Nicholas John Bennett, MB, BCh, PhD, is a member of the following medical societies: Alpha Omega Alpha and American Academy of Pediatrics

Disclosure: Nothing to disclose.

Coauthor(s)

Joseph Domachowske, MD  Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York Upstate Medical University

Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Asad A Khan, MD  Fellow, Department of Internal Medicine, Division of Infectious Diseases, Louisiana State University Health Science Center

Asad A Khan, MD is a member of the following medical societies: American College of Physicians and Infectious Diseases Society of America

Disclosure: Nothing to disclose.

John W King, MD  Professor of Medicine, Chief, Section of Infectious Diseases, Director, Viral Therapeutics Clinics for Hepatitis, Louisiana State University Health Sciences Center; Consultant in Infectious Diseases, Overton Brooks Veterans Affairs Medical Center

John W King, MD is a member of the following medical societies: American Association for the Advancement of Science, American College of Physicians, American Federation for Medical Research, American Society for Microbiology, Association of Subspecialty Professors, Infectious Diseases Society of America, and Sigma Xi

Disclosure: emedicine $50.00 Author of chapter; MERCK Grant/research funds Other

J Thomas Cross, Jr, MD, MPH  Vice President, Education, MedStudy Corporation

J Thomas Cross, Jr, MD, MPH is a member of the following medical societies: American Academy of Pediatrics, American College of Physicians, Infectious Diseases Society of America, and Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Specialty Editor Board

José Rafael Romero, MD  Director of Pediatric Infectious Diseases Fellowship Program, Associate Professor, Department of Pediatrics, Combined Division of Pediatric Infectious Diseases, Creighton University/University of Nebraska Medical Center

José Rafael Romero, MD is a member of the following medical societies: American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, New York Academy of Sciences, and Pediatric Infectious Diseases Society

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Joseph Domachowske, MD  Professor of Pediatrics, Microbiology and Immunology, Department of Pediatrics, Division of Infectious Diseases, State University of New York Upstate Medical University

Joseph Domachowske, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American Society for Microbiology, Infectious Diseases Society of America, Pediatric Infectious Diseases Society, and Phi Beta Kappa

Disclosure: Nothing to disclose.

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: Novartis Honoraria Speaking and teaching

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: Nothing to disclose.

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Number of identified cases of primary amoebic meningoencephalitis (PAM), 1937-2007.
 
 
 
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