Role of Dexamethasone in Meningoencephalitis
Dexamethasone should be administered as adjunctive therapy in bacterial meningitis, particularly for pneumococcal and Haemophilus influenzae meningitis, but should be discontinued for Listeria monocytogenes infections and considered for discontinuation in Neisseria meningitidis infections. 1
Mechanism and Rationale
Dexamethasone works by attenuating the subarachnoid space inflammatory response during bacterial meningitis, which is a major factor contributing to morbidity and mortality. This anti-inflammatory effect can decrease pathophysiologic consequences such as:
- Cerebral edema
- Increased intracranial pressure
- Altered cerebral blood flow
- Cerebral vasculitis
- Neuronal injury mediated by pro-inflammatory cytokines 2
Administration Protocol
Timing
- Optimal timing: 10-20 minutes before or with the first dose of antibiotics
- Can still be effective if started within 4 hours after initiation of antibiotic treatment 1
- If antibiotics were started >4 hours ago, do not initiate dexamethasone 1
Dosage
Pathogen-Specific Recommendations
Streptococcus pneumoniae
- Continue dexamethasone for the full 4-day course
- Significantly reduces unfavorable outcomes (26% vs 52% with placebo) and mortality (14% vs 34% with placebo) 1
- If dealing with resistant strains, consider adding rifampin to vancomycin plus third-generation cephalosporin regimen 1
Haemophilus influenzae
- Continue dexamethasone to reduce hearing impairment
- Strong evidence supports benefit in reducing hearing impairment (combined OR, 0.31; 95% CI, 0.14–0.69) 2, 1
Neisseria meningitidis
- Consider discontinuing dexamethasone as evidence for benefit is less conclusive 1
Listeria monocytogenes
- Discontinue dexamethasone due to its association with increased mortality 1
Evidence in Non-Bacterial Meningoencephalitis
For viral or non-purulent meningoencephalitis, the evidence is limited. Case reports suggest that dexamethasone may help reduce diffuse brain edema in non-purulent meningoencephalitis, with rapid improvement of clinical symptoms and significant reduction of brain edema on CT imaging 3. However, this is based on limited case reports rather than robust clinical trials.
Clinical Benefits
- Earlier resolution of fever, headache, and altered consciousness 4
- Improved CSF inflammatory parameters (glucose, protein, WBC count) by day 5 4
- Lower incidence of cranial nerve involvement 4
- Potential reduction in neurological and audiological sequelae 5
Potential Risks and Considerations
- May decrease penetration of antibiotics into CSF, particularly vancomycin and ceftriaxone, potentially delaying CSF sterilization in resistant pneumococcal infections 6
- Increased risk of hippocampal neuronal apoptosis observed in animal models of both Gram-positive and Gram-negative meningitis 7
- Less beneficial in low-income countries with high rates of malnutrition and HIV infection 2
- Not recommended for neonates due to insufficient evidence 1
Treatment Algorithm
For suspected bacterial meningitis in non-neonates:
- Start dexamethasone before or with the first antibiotic dose
- Continue for 4 days in adults, 2-4 days in children
After pathogen identification:
- Continue for S. pneumoniae or H. influenzae
- Discontinue for Listeria monocytogenes
- Consider discontinuing for N. meningitidis based on clinical assessment
For viral or non-purulent meningoencephalitis:
- Evidence is limited, but may be considered in cases with significant cerebral edema
- Monitor closely for clinical improvement and reduction in brain edema
Monitor for:
- Clinical improvement (fever, neck rigidity, consciousness)
- CSF inflammatory parameters
- Potential adverse effects of dexamethasone
By following this algorithm and considering pathogen-specific recommendations, clinicians can optimize the use of dexamethasone in meningoencephalitis to improve patient outcomes while minimizing potential risks.