What is meningitis, including its assessment, pathophysiology, and treatment?

Meningitis: Assessment, Pathophysiology, and Pharmacology

Meningitis is an inflammation of the meninges (the protective membranes covering the brain and spinal cord) that requires prompt recognition and treatment, with bacterial meningitis being a medical emergency requiring immediate antibiotic therapy to reduce mortality and morbidity. 1

Pathophysiology

Meningitis involves inflammation of the meninges and subarachnoid space. The pathophysiological process differs based on the causative agent:

Bacterial Meningitis

• Bacteria enter the subarachnoid space either through:
  • Direct invasion from adjacent structures (sinuses, mastoids)
  • Hematogenous spread (bloodstream)
  • Direct introduction (trauma, surgery)
• Once in the CSF, bacteria multiply rapidly due to lack of effective immune response
• Bacterial cell wall components trigger inflammatory cascade
• Inflammation leads to:
  • Increased blood-brain barrier permeability
  • Cerebral edema
  • Increased intracranial pressure
  • Reduced cerebral blood flow
  • Potential cerebral herniation 2, 3

Viral Meningitis

• Viruses typically enter through respiratory or gastrointestinal route
• Reach the CNS via bloodstream or neural pathways
• Cause less severe inflammation than bacterial meningitis
• Generally self-limiting with better outcomes 4, 5

Clinical Assessment

Key Symptoms and Signs

• Classic triad: Fever, headache, and neck stiffness (meningism)
• Other common presentations:
  • Photophobia
  • Altered mental status
  • Nausea and vomiting
  • Seizures
  • Petechial or purpuric rash (especially in meningococcal disease)
  • Kernig's and Brudzinski's signs (though sensitivity and specificity are variable) 1, 3

Risk Factors

• Age extremes (infants and elderly)
• Immunocompromised states
• Recent neurosurgery or head trauma
• Anatomic defects (CSF leaks)
• Close contact with meningitis cases
• Crowded living conditions (dormitories, military barracks) 3, 6

Diagnostic Workup

1. Lumbar puncture (cornerstone of diagnosis):

   • CSF analysis:
     • Bacterial: Elevated WBC (neutrophil predominance), elevated protein, decreased glucose, positive Gram stain and culture
     • Viral: Mild to moderate WBC (lymphocyte predominance), normal to slightly elevated protein, normal glucose, negative Gram stain 1, 5

2. When to perform CT before LP:

   • Altered mental status
   • Focal neurological deficits
   • Papilledema
   • History of immunocompromise or CNS disease
   • Seizures 1, 3

3. Other tests:

   • Blood cultures (positive in 50-80% of bacterial meningitis)
   • Complete blood count
   • CSF PCR for viral pathogens
   • Serum inflammatory markers (CRP, procalcitonin) 1, 4

Pharmacological Management

Bacterial Meningitis

1. Empiric Antibiotic Therapy (start immediately if bacterial meningitis suspected):

   • Adults (18-50 years): Ceftriaxone 2g IV q12h + Vancomycin 15-20 mg/kg IV q8-12h
   • Adults >50 years or immunocompromised: Add Ampicillin 2g IV q4h (for Listeria coverage)
   • Duration: 7-14 days depending on pathogen 1, 7, 3

2. Adjunctive Therapy:

   • Dexamethasone 10mg IV q6h for 4 days (start before or with first antibiotic dose)
   • Discontinue if Listeria monocytogenes is confirmed 1, 3

3. Pre-hospital Antibiotics:

   • Indicated when:
     • Signs of meningococcal disease (e.g., rash with meningism)
     • Signs of severe sepsis
     • Anticipated delay >1 hour to hospital arrival
   • Benzylpenicillin 1200mg IM/IV or Ceftriaxone 2g IM/IV 1

Viral Meningitis

• Primarily supportive care:
  • Adequate pain control
  • Maintenance of hydration
  • Rest
• No proven benefit for routine use of aciclovir or valaciclovir for HSV or VZV meningitis
• If encephalitis is suspected (altered consciousness, personality changes), start IV aciclovir immediately 4, 5

Complications and Sequelae

Acute Complications

• Cerebral edema and increased intracranial pressure
• Seizures
• Cerebrovascular complications (infarctions, hemorrhage)
• Hydrocephalus
• Septic shock (especially in meningococcal disease) 1

Long-term Sequelae

• Hearing loss (5-35% of bacterial meningitis)
• Cognitive impairment
• Seizure disorders
• Motor deficits
• Visual disturbances
• Psychological issues 1

Prevention

1. Vaccination against common pathogens:

   • Pneumococcal vaccines
   • Meningococcal vaccines
   • Haemophilus influenzae type b vaccine 3, 6

2. Chemoprophylaxis for close contacts of meningococcal meningitis cases 1, 5

Important Clinical Pitfalls

• Delayed antibiotic administration: Start antibiotics immediately if bacterial meningitis is suspected, even before LP or imaging
• Misdiagnosis: Viral vs. bacterial meningitis can be difficult to distinguish clinically
• Missing encephalitis: If there are signs of encephalitis, start IV aciclovir immediately
• Inadequate follow-up: Arrange hearing assessment and neuropsychological evaluation for survivors 1, 4

Follow-up Care

• Hearing assessment during admission or within 4 weeks
• Neuropsychological evaluation for cognitive deficits
• Staged return to work/studies
• Patient education about potential sequelae 1