Clinical scenario: Fever | Headache | confusion | swimming in stagnant water
An 11-year-old boy is brought to the emergency department with high-grade fever, severe headache, repeated vomiting, and progressive confusion for 24 hours. Five days earlier, he had been swimming and diving in a stagnant local irrigation canal after heavy monsoon rains.
On examination, he is febrile (39.8°C), agitated, has neck stiffness, and a GCS of 11/15.
Investigations:
- WBC: 18,900/µL (90% neutrophils)
- CT brain: Mild diffuse cerebral edema
- CSF:
- Opening pressure: 320 mmH₂O
- WBC: 2,400/µL (95% neutrophils)
- Protein: 210 mg/dL
- Glucose: 22 mg/dL (blood glucose 100 mg/dL)
- Gram stain: No organisms seen
Despite empirical treatment for bacterial meningitis, his neurological status continues to deteriorate rapidly.
Which of the following is the most appropriate next step in management?
A. Amphotericin B + miltefosine
B. Acyclovir
C. Ceftriaxone + vancomycin
D. RIPE therapy
E. Metronidazole
Correct answer & Explanation:
Correct Answer: A. Amphotericin B + miltefosine
Explanation
This child has Primary Amoebic Meningoencephalitis (PAM) caused by Naegleria fowleri, a free-living thermophilic amoeba found in warm freshwater such as lakes, ponds, hot springs, and irrigation canals. Infection occurs when contaminated water is forcefully inhaled through the nose, allowing trophozoites to migrate along the olfactory nerves through the cribriform plate into the brain.
Key diagnostic clues include:
- Recent freshwater exposure during hot/rainy weather
- Rapid onset (typically 2–8 days after exposure)
- Fulminant meningoencephalitis
- CSF resembling bacterial meningitis (neutrophilic pleocytosis, low glucose, high protein)
- Negative Gram stain and bacterial cultures
- Motile trophozoites on fresh wet mount of CSF (diagnostic)
Because mortality exceeds 95%, treatment should begin immediately without waiting for confirmatory tests.
Current recommended therapy includes:
- Intravenous liposomal or conventional amphotericin B
- Intrathecal/intraventricular amphotericin B when feasible
- Miltefosine
- Combination therapy with agents such as azithromycin, rifampicin, fluconazole, and/or dexamethasone according to expert recommendations and individual clinical circumstances, together with aggressive neurocritical care and intracranial pressure management.
Why the other options are incorrect
- B. Ceftriaxone plus vancomycin and dexamethasone: Appropriate empirical therapy for bacterial meningitis but ineffective against Naegleria fowleri.
- C. Intravenous acyclovir: Used for herpes simplex encephalitis.
- D. Antituberculous therapy: Tuberculous meningitis has a more subacute presentation and lymphocytic CSF predominance.
- E. Oral metronidazole alone: Has no established role as effective monotherapy for PAM.
Learning Point: In any patient with rapidly progressive meningoencephalitis after recent freshwater swimming, especially when CSF resembles bacterial meningitis but Gram stain is negative, Naegleria fowleri should be suspected immediately, and treatment with amphotericin B-based combination therapy including miltefosine should be started urgently.
