What is the recommended approach for diagnosing and treating meningitis?

Diagnosing Meningitis: A Comprehensive Approach

The definitive diagnosis of meningitis requires cerebrospinal fluid (CSF) examination through lumbar puncture (LP), which should be performed within 1 hour of hospital arrival if no contraindications exist. 1

Clinical Presentation

• In adults, the most common symptoms include fever (77-97%), headache (58-87%), neck stiffness (65-83%), and altered mental status (30-69%), though the classic triad of fever, neck stiffness, and altered mental status is present in only 41-51% of cases 2
• In children beyond neonatal age, common symptoms include fever (92-93%), headache (78%), neck stiffness (40-82%), and vomiting (58-67%) 2
• Neonates often present with nonspecific symptoms, making diagnosis more challenging 2
• A petechial or hemorrhagic rash is present in 20-52% of adults and is highly indicative of meningococcal infection (>90% of cases) 2
• Clinical signs alone have poor sensitivity for diagnosing meningitis (neck stiffness 31-51%, Kernig sign 11-53%, Brudzinski sign 9-66%), and their absence cannot rule out meningitis 2

Diagnostic Algorithm

Step 1: Initial Assessment

• Stabilize airway, breathing, and circulation
• Document Glasgow Coma Scale (GCS) score
• Assess for signs of shock, sepsis, or rapidly evolving rash 1
• Obtain blood cultures within the first hour of hospital arrival, before antibiotic administration 1, 3

Step 2: Evaluate for LP Contraindications

• Contraindications include: focal neurological signs, papilledema, continuous or uncontrolled seizures, GCS ≤12, immunocompromised state, history of CNS disease, and new onset seizure within 1 week 1
• If contraindications exist, proceed to neuroimaging before LP 2

Step 3: Perform LP and CSF Analysis

• If no contraindications exist, perform LP within 1 hour of hospital arrival 1
• Collect CSF for the following tests:
  • Cell count and differential
  • Glucose and protein levels
  • Gram stain
  • Culture
  • Consider PCR for viral, bacterial pathogens if available 2, 1

Step 4: Interpret CSF Findings

• CSF culture is positive in 60-90% of bacterial meningitis cases 2
• CSF Gram stain has excellent specificity but varying sensitivity depending on the organism 2
• CSF lactate >3.5 mmol/L is a good predictor of bacterial meningitis 4
• If CSF culture and Gram stain are negative, PCR has additional value in pathogen identification 2

Special Considerations

• Timing of LP and antibiotics:

  • If LP can be performed promptly, obtain CSF before starting antibiotics 1
  • If LP is delayed, start empiric antibiotics immediately after blood cultures 1, 3
  • CSF culture positivity decreases by 10-20% if antibiotics are given before LP 2
  • LP performed within 4 hours of antibiotic administration still has a 73% chance of positive culture, compared to only 11% if performed later 5

• Additional diagnostic tests:

  • Blood cultures have varying positivity rates: 75% for pneumococcal meningitis, 50-90% for H. influenzae meningitis, and 40-60% for meningococcal meningitis 2
  • Serum inflammatory markers (CRP, procalcitonin) may help differentiate bacterial from viral meningitis, with procalcitonin threshold between 1-2 ng/ml having good discriminatory value 2, 4
  • Latex agglutination testing has limited incremental value 2
  • Immunochromatographic antigen testing may be useful but requires further study 2

• Pitfalls to avoid:

  • Delaying antibiotics while waiting for LP or neuroimaging increases mortality 1, 3
  • Sending patients for unnecessary CT scans when no contraindications to immediate LP exist 5
  • Failing to recognize that meningitis can occasionally occur without CSF pleocytosis (rare but reported) 6
  • Relying solely on clinical signs to rule out meningitis 2

Treatment Approach

• Start antibiotics as soon as possible after bacterial meningitis is suspected, ideally within 1 hour of hospital arrival 3
• For adults, the recommended empiric regimen is cefotaxime or ceftriaxone plus vancomycin or rifampicin 3
• For older adults or immunocompromised patients, add amoxicillin/ampicillin/penicillin G to cover Listeria monocytogenes 3
• For meningitis, ceftriaxone dosing is 100 mg/kg/day (not to exceed 4 grams daily) 7
• Administer dexamethasone before or at the time of first antibiotic dose 3

By following this systematic approach to diagnosing meningitis, clinicians can ensure timely identification and appropriate management of this potentially life-threatening condition.