Management of Suspected Meningoencephalitis in a 4-Year-Old
Start intravenous acyclovir immediately along with empiric antibiotics (ceftriaxone and vancomycin) until bacterial meningitis and HSV encephalitis are definitively excluded. 1, 2, 3
Rationale for Combined Therapy
The CSF profile of clear fluid with lymphocytosis and low glucose creates diagnostic uncertainty that mandates broad coverage:
Lymphocytic pleocytosis with low glucose does NOT exclude bacterial meningitis, as partially treated bacterial meningitis, tuberculous meningitis, and listeriosis can present identically 1, 2
HSV encephalitis can present with normal or minimally abnormal CSF in 5-10% of cases, and the decreased level of consciousness with recent viral illness and seizure are classic features requiring immediate acyclovir 1, 2
Bacterial meningitis typically shows neutrophil predominance, but approximately 10% present with lymphocyte predominance, making bacterial infection still possible 1
Specific Treatment Protocol
Immediate Antimicrobial Therapy
Acyclovir 500 mg/m² IV every 8 hours (for age 4 years) must be started within 6 hours of admission, as delays beyond 48 hours significantly worsen outcomes in HSV encephalitis (mortality 70% untreated vs 20-30% with treatment) 1, 3, 4
Ceftriaxone 100 mg/kg/day IV plus vancomycin 60 mg/kg/day IV to cover pneumococcal meningitis (including resistant strains), meningococcal meningitis, and other bacterial pathogens 5, 6
Continue acyclovir for 14-21 days if HSV is confirmed; discontinue antibiotics once bacterial meningitis is excluded by culture and clinical course 1, 3
Why Not Corticosteroids Alone?
Corticosteroids should NOT be used routinely in HSV encephalitis as they have strong immunomodulatory effects that could theoretically facilitate viral replication, and their role remains controversial pending results of ongoing randomized controlled trials 1
Dexamethasone 0.15 mg/kg IV every 6 hours for 4 days can be added when treating empirical bacterial meningitis, given with or within 24 hours of the first antibiotic dose 3
However, corticosteroids alone without antimicrobial coverage would be dangerous given the differential diagnosis 1
Critical Diagnostic Workup
Immediate CSF Studies
Send CSF PCR for HSV-1, HSV-2, VZV, and enteroviruses immediately, as these account for 90% of viral CNS infections 2
Obtain CSF bacterial culture and Gram stain to exclude partially treated bacterial meningitis 2
Measure CSF lactate, as levels <2 mmol/L effectively rule out bacterial disease 2
Send CSF for tuberculosis studies (culture, AFB smear, TB PCR) given the low glucose and lymphocytic pleocytosis pattern 7, 2
Neuroimaging Requirements
- Obtain brain MRI with and without contrast to identify temporal lobe enhancement (HSV encephalitis), basilar meningeal enhancement (TB or fungal meningitis), or other pathology 2
Follow-Up Strategy
Repeat lumbar puncture in 24-48 hours if initial CSF HSV PCR is negative and clinical suspicion remains high, as HSV PCR can be negative early in disease course 1, 2
Monitor for acyclovir nephrotoxicity and ensure adequate hydration to prevent crystalluria 3
Transfer to pediatric intensive care if the patient continues to deteriorate despite appropriate treatment 3
Common Pitfalls to Avoid
Never assume lymphocytic CSF means "just viral" - TB meningitis, partially treated bacterial meningitis, and listeriosis all present with lymphocytic pleocytosis and low glucose 1, 7, 2
Never delay acyclovir waiting for HSV PCR results - the decreased LOC and seizure with recent viral illness warrant immediate treatment 1, 2
Never use third-generation cephalosporin monotherapy - it is less effective than combination therapy and misses important pathogens 8