What are the diagnostic tests and initial treatment for suspected meningitis?

Diagnostic Tests and Initial Treatment for Suspected Meningitis

In suspected meningitis, lumbar puncture (LP) should be performed within 1 hour of hospital arrival if safe to do so, followed immediately by appropriate antimicrobial therapy, with blood cultures obtained before treatment initiation. 1

Initial Assessment and Stabilization

• Immediate stabilization of airway, breathing, and circulation is the first priority 1
• Document Glasgow Coma Scale (GCS) score to assess severity and monitor changes 1
• Obtain blood cultures within the first hour of hospital arrival, before antibiotic administration 1
• Assess for signs of shock, sepsis, or rapidly evolving rash which would alter management approach 1

Diagnostic Tests

Lumbar Puncture

• Perform LP within 1 hour of hospital arrival if no contraindications exist 1
• LP contraindications requiring neuroimaging first 1, 2:
  • Focal neurological signs
  • Papilledema
  • Continuous or uncontrolled seizures
  • GCS ≤ 12
  • Immunocompromised state
  • History of CNS disease
  • New onset seizure within 1 week
  • Decerebrate posturing (absolute contraindication) 2

CSF Analysis

• Gram stain: Rapid identification in 60-90% of bacterial meningitis cases with specificity of 97% 1
• CSF cell count and differential, glucose, and protein levels 1, 3
• CSF culture: Gold standard but results take up to 48 hours 1, 3
• Bacterial antigen tests (latex agglutination): Results available in 15 minutes but variable sensitivity (50-100% depending on pathogen) 1
• CSF lactate >3.5 mmol/L strongly suggests bacterial etiology 4
• Consider PCR testing, especially in patients who received antibiotics before LP 5, 6

Additional Tests

• Serum procalcitonin: Useful for differentiating bacterial from viral meningitis (threshold 1-2 ng/ml) 4
• Blood cultures: Essential before antibiotic administration 1

Initial Treatment Approach

Patients with Suspected Meningitis (without shock/sepsis)

• Perform LP within 1 hour if safe to do so 1
• Start antibiotics immediately after LP and within the first hour 1
• If LP cannot be performed within 1 hour, obtain blood cultures and start antibiotics immediately, then perform LP as soon as possible (preferably within 4 hours of antibiotic initiation) 1

Patients with Sepsis or Rapidly Evolving Rash

• Obtain blood cultures and start antibiotics immediately 1
• Begin fluid resuscitation with initial 500 ml crystalloid bolus 1
• Follow Surviving Sepsis guidelines 1
• Defer LP until patient is stabilized 1

Antimicrobial Therapy

• For meningitis: Ceftriaxone 2g IV every 12-24 hours (total daily dose 4g) 7
• For children: 100 mg/kg/day (not exceeding 4g daily) 7
• If anaphylaxis to beta-lactams, alternative antibiotics should be given in hospital setting 1
• Duration typically 7-14 days depending on pathogen and clinical response 7

Critical Time Points

• Senior clinical review within the first hour 1
• Blood cultures within 1 hour of arrival 1
• LP within 1 hour if no contraindications 1
• Antibiotics within 1 hour (after LP if possible, or immediately after blood cultures if LP delayed) 1
• If antibiotics given before LP, perform LP within 4 hours of antibiotic initiation when possible 1

Common Pitfalls to Avoid

• Delaying antibiotics while waiting for LP or neuroimaging - this increases mortality 1, 2
• Failing to recognize signs of increased intracranial pressure that contraindicate immediate LP 1, 2
• Underestimating severity based on initial presentation - meningitis can deteriorate rapidly 1
• Neglecting to obtain blood cultures before antibiotic administration 1
• Relying solely on negative bacterial antigen tests to rule out bacterial meningitis 1