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Internal Medicine: A Guide to Clinical Therapeutics

Chapter 30. Meningitis

Allana J. Sucher

Bacterial etiology of meningitis varies by patient age, immune status, & history of neurosurgical procedure or head trauma
Aseptic meningitis: all nonbacterial causes (viruses, fungi, parasites, medications, cochlear implants, malignancies)
Nasopharyngeal (bacteria) or mucosal surface (viral) colonization → bacteremia or viremia → invasion into CNS → replication → meningeal inflammation → neurological sequelae

Table 30-1 Etiology of Bacterial Meningitis by Age & Predisposing Factors (Clin Infect Dis 2004;39:1267)

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Table 30-1 Etiology of Bacterial Meningitis by Age & Predisposing Factors (Clin Infect Dis 2004;39:1267)

Predisposing Condition

Organism

Age*

2–50y

>50y

Streptococcus pneumoniae, Neisseria meningitidis

S. pneumoniae, N. meningitidis, Listeria monocytogenes, enteric gram-negatives (Escherichia coli)

Head trauma

Basilar skull fracture

Penetrating trauma

S. pneumoniae, Streptococcus pyogenes, Haemophilus influenzae

Staphylococcus aureus, Staphylococcus epidermidis, aerobic gram-negatives (including Pseudomonas aeruginosa)

Postneurosurgery

S. aureus, S. epidermidis, aerobic gram-negatives (including P. aeruginosa)

*Any age that is immunocompromised is at risk for infection by L. monocytogenes.

Pertinent Positive Labs

Lumbar puncture for cerebrospinal fluid (CSF) analysis
CSF laboratory values & Gram stain help determine cause of meningitis
Further work-up of aseptic meningitis: PCR for HSV/enteroviruses; CSF cryptococcal antigen for cryptococcal meningitis in immunosuppressed patients (in HIV, CD4+ <50cells/mm3)

Table 30-2 CSF Laboratory Interpretation (Lee M. Basic Skills in Interpreting Laboratory Data, 4th ed., 2009)

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Table 30-2 CSF Laboratory Interpretation (Lee M. Basic Skills in Interpreting Laboratory Data, 4th ed., 2009)

Normal

Bacterial Meningitis

Aseptic Meningitis

WBC (mm3)

>1000

5–500

Differential

No predominance

>80% PMNs

>50% lymphocytes

Protein (mg/dL)

<50

>100

30–150

Glucose (mg/dL)

2/3 serum

<1/2 serum

<30–70

Gram stain (Table 30-3)

Negative

60–90% sensitive

Negative

CSF: cerebrospinal fluid; PMNs: polymorphonuclear neutrophils (segmented neutrophils).

Table 30-3 Gram Staining Characteristics of Bacteria (Levinson W. Review of Medical Microbiology & Immunology, 2010)

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Table 30-3 Gram Staining Characteristics of Bacteria (Levinson W. Review of Medical Microbiology & Immunology, 2010)

S. pneumoniae

Gram-positive diplococci (α-hemolytic)

N. meningitidis

Gram-negative cocci

L. monocytogenes

Gram-positive rods

E. coli

Gram-negative rods (lactose positive)

S. pyogenes

Gram-positive cocci (β-hemolytic)

H. influenzae

Gram-negative rods

S. aureus

Gram-positive cocci in clusters (coagulase positive)

S. epidermidis

Gram-positive cocci in clusters (coagulase negative)

P. aeruginosa

Gram-negative rods (lactose negative, oxidase positive)

*All microorganisms in this table are aerobic.

Treatment goals: ameliorate signs & symptoms, eradicate infection, prevent development of neurological sequelae

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Clinical Pearl 30-1

Start empiric ABX as soon as possible in all patients with suspected meningitis

Principles of treatment: high-dose parenteral therapy; agent must penetrate blood-brain barrier, be bactericidal in the CSF, & have antimicrobial activity against infecting ...

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