14: Meningitis

Question 1

What is special about meningitis?

Answer 1

• CSF is privileged space: litle room for inflammation, no complement, minimal immunoglobulin, no PMNs
• Well-defended space: Blood brain barrier provided by specialized endothelial-capillary junctions
• Only certain organisms - high grade bacteremia - are recognized by specific receptors that allows for their passage

Question 2

What are the top three organisms in neonate meningitis?

Answer 2

• GBS (S. agalactiae)
  
  • Common commensal flora (childbearing women): vertical transmission
  • Virulence factor: polysaccharide capsule evades innate immunity
  • High grade bacteremia: poor neonatal host defenses (PMN function, complement function, lack of Ab for phagocytosis)
  • Ppx: penicillin
• E. coli K1 (capsule)
  
  • GNR
  • Part of maternal fecal flora
  • Virulence factor: human-like K1 capsular antigen evades adaptive immune system
  • Frequent abx resistance (rx vanco)
• Listeria monocytogenes
  
  • GPR (tumbling motility)
  • Found in animal feces
  • Contamination of unpasteurized animal products, organic produce
  • Rx: ampicillin

Question 3

What is the clinical presentation of neonatal/young infant meningitis?

Answer 3

• Sepsis
• High/low WBC
• Irritability/listlessness
• High fever
• Bulging fontanelle (late finding)

Question 4

What is the pathophysiology of meningitis?

Answer 4

1. High-grade bacteremia
2. Bacterial breach of sterile CNS
3. Influx of PMNs
4. Severe, unreg’d inflammatory response
5. Edema, platelets, clotting

• Pneumolysin stimulates neuronal apoptosis (triggers inflammosome)
• Release of NO –> tissue damage

Question 5

What are the top three organisms in infant/children meningitis?

Answer 5

• S. pneumoniae
  
  • Virulence: cell wall fragments –> inflammatory reaction; polysaccharide capsule
  • Transmission = droplet
  • Rx: steroids, then penicillin (but need 20x MIC of organism to reach CSF)
  • Poor prognosis b/c of high level inflammation
  • Prevent w/ 13-valent conjugate vaccine (Prevnar) or 23-valent polysaccharide vaccine in adults
• Neisseria meningitidis
  
  • GND
  • Virulence: polysaccharide capsule
  • Transmission: nasopharyngeal secretions/droplet
  • Complication: coagulopathy (DIC)
  • Sx: truncal petechiae
  • Risk factors: college, military, travelers to sub-Saharan Africa, complement deficiency
  • Vaccine: A, C, Y, W 135 (not B due to sialic acid epitopes –> cross-reactive)
  • Ppx: Rifampin, ciprofloxacin, ceftriaxone
• Haemophilus Influenza type B
  
  • Virulence: IgA proteases, polysaccharide capsule
  • Effective universal vaccination campaign (now fairly rare)
  • PRP conjugate vaccine
  • Rx: give corticosteroids first, then amoxacillin

Question 6

Describe how to diagnose meningitis

Answer 6

• Lumbar puncture:
  
  • Low glucose, high protein, high WBC
  • Any PMNs = red flag
• Gram stain: GP/GN for abx
• CT: increased intracranial pressure
• MRI: later in management

Question 7

What are sequellae of meningitis?

Answer 7

• Hearing loss (15-20%)
• Seizure disorder
• Major neurological dysfunction
• Hydrocephalus
• Soft neruological dysfunction (ADD, behavioral abnormalities)

Question 8

What are the top two organisms in adult meningitis?

Answer 8

• N. meningitidis
• S. pneuoniae