What are the signs, symptoms, and cerebrospinal fluid (CSF) findings of amebic meningitis?

Amebic Meningitis: Signs, Symptoms, and CSF Findings

Primary amebic meningoencephalitis (PAM) presents with symptoms indistinguishable from bacterial meningitis, including fever, headache, neck stiffness, and altered mental status, but does not respond to standard antibiotic therapy and has a mortality rate exceeding 95% without prompt, specific treatment. 1

Clinical Presentation

Signs and Symptoms

• Initial presentation (typically within 1-7 days after exposure):

  • Severe frontal headache (prominent early symptom)
  • Fever (intermittent)
  • Nausea and vomiting
  • Neck stiffness/pain upon flexion
  • Altered mental status

• Disease progression (rapid deterioration within days):

  • Confusion and abnormal behavior
  • Seizures
  • Hemiparesis and focal neurological deficits
  • Loss of balance and body control
  • Progression to coma 1, 2

Key Risk Factors

• Recreational exposure to warm freshwater (lakes, ponds, inadequately chlorinated swimming pools)
• Recent history of swimming or bathing in standing bodies of freshwater
• Nasal water exposure (including sinus lavage with neti pots or ritual nasal ablution)
• Summer months (when water temperatures are higher) 1

CSF Findings

• Increased white blood cell count (predominantly lymphocytes in some cases)
• Elevated protein levels
• Low glucose concentration
• Presence of highly motile trophozoites of Naegleria fowleri on wet mount preparation
• Negative bacterial and fungal cultures
• Negative cryptococcal antigen testing 3, 4

Diagnostic Approach

Essential Diagnostic Steps

1. Cerebrospinal fluid examination - the definitive diagnostic test

   • Direct microscopic examination for motile trophozoites
   • Culture on non-nutrient agar
   • PCR testing when available 5, 4

2. Neuroimaging (CT/MRI)

   • May show non-specific findings or be normal
   • Can help rule out other causes of meningitis 3

Diagnostic Pitfalls

• Mistaking PAM for bacterial meningitis due to similar presentation
• Failure to obtain history of freshwater exposure
• Relying solely on standard bacterial and fungal CSF studies
• Delaying specific anti-amebic treatment while waiting for definitive diagnosis 6

Treatment Considerations

Early recognition and aggressive treatment are crucial for survival. The mortality rate exceeds 95%, with only a few documented survivors worldwide 1, 4.

Potentially Effective Therapeutic Regimens

• Amphotericin B (intravenous and intrathecal)
• Miltefosine (recently shown to improve survival)
• Combination therapy with rifampicin, voriconazole, and other antimicrobials 2, 4

Prevention

• Avoid swimming in warm freshwater bodies, especially during summer months
• Use nose clips when swimming in potentially contaminated water
• Avoid submerging the head in hot springs and other untreated thermal waters
• Use sterile or properly treated water for nasal irrigation 1

PAM should be included in the differential diagnosis of any patient presenting with rapidly progressive meningoencephalitis following water exposure or nasal lavage, as early initiation of appropriate treatment is critical for survival 1.