Primary Amebic Meningoencephalitis

Aka: Primary Amebic Meningoencephalitis, Primary Amoebic Meningoencephalitis, Primary Amebic Encephalitis, Naegleria Fowleri Encephalitis, Naegleria Fowleri

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II. Epidemiology

  1. Rare, but lethal Encephalitis (4 cases per year in U.S.)

III. Pathophysiology

  1. Naegleria Fowleri is a free living amoeba inhabiting free water and moist soils
  2. Exposure typically occurs with swimming in fresh water lakes, rivers or hot springs
  3. Transmitted via the nasal cavity and secondary Sinusitis, and CNS Infection via Cribiform Plate

IV. Findings

  1. See Meningitis
  2. See Encephalitis

V. Labs

  1. CSF Exam is similar to Bacterial Meningitis findings
    1. High CSF White Blood Cell Count with Neutrophil predominance
    2. High CSF Protein
    3. Low CSF Glucose
  2. CSF Microscopy
    1. CSF Gram Stain and Culture negative for Bacteria
    2. Motile amoeba may be seen on microscopy

VI. Differential Diagnosis

  1. See Meningitis
  2. See Encephalitis
  3. Chronic Granulomatous Encephalitis (Acanthamoeba, Balamuthia mandrllaris)
    1. More insidious Encephalitis course
    2. Primarily in Immunocompromised patients

VII. Management

  1. Amphoteracin B 1.5 mg/kg/day (IV and consider intrathecal) AND
  2. Rifampin 10 mg/kg/day AND
  3. Fluconazole 10 mg/kg/day IV or orally AND
  4. Azithromycin 500 mg IV or orally AND
  5. Miltefosine (Impavido) 50 mg orally three times daily
    1. As of 2017, investigational, and only available from CDC (consult early and urgently if suspected case)

VIII. Differential Diagnosis

  1. See Encephalitis
  2. See Meningitis
  3. Other amebic meningoencephalitis (present as Chronic Granulomatous Meningitis)
    1. Balamuthia mandrillaris
    2. Acanthameba

IX. Prognosis

  1. Mortality: 90-95% (typically in the first week of infection)

X. References

  1. Gladwin, Trattler and Mahan (2014) Clinical Microbiology, Medmaster, Fl, p. 339-40
  2. (2017) Sanford guide, accessed 5/4/2017
  3. Perkins (2017) Am Fam Physician 95(9): 554-60 [PubMed]

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