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30-04: Infections of the Central Nervous System

Peter V. Chin-Hong; B. Joseph Guglielmo

ESSENTIALS OF DIAGNOSIS

  • CNS infection is a medical emergency.

  • Symptoms and signs common to all CNS infections include headache, fever, sensorial disturbances, neck and back stiffness, positive Kernig and Brudzinski signs, and cerebrospinal fluid abnormalities.

GENERAL CONSIDERATIONS

Infections of the CNS can be caused by almost any infectious agent, including bacteria, mycobacteria, fungi, spirochetes, protozoa, helminths, and viruses.

ETIOLOGIC CLASSIFICATION

CNS infections can be divided into several categories that usually can be readily distinguished from each other by cerebrospinal fluid examination as the first step toward etiologic diagnosis (Table 30–1) (eFigure 30–2).

Table 30–1.Typical cerebrospinal fluid findings in various central nervous system diseases (listed in alphabetical order after Normal).
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Table 30–1. Typical cerebrospinal fluid findings in various central nervous system diseases (listed in alphabetical order after Normal).
Diagnosis Cells/mcL Glucose (mg/dL) Protein (mg/dL) Opening Pressure
Normal 0–5 lymphocytes 45–851 15–45 70–180 mm H2O
Aseptic meningitis, viral meningitis, or meningoencephalitis2 25–2000 (0.025–2.0 × 109/L), mostly lymphocytes3 Normal or low High (> 50) Slightly elevated
Granulomatous meningitis (mycobacterial, fungal)3 100–1000 (0.1–1.0 × 109/L), mostly lymphocytes3 Low (< 45) High (> 50) Moderately elevated
“Neighborhood reaction”4 Variably increased Normal Normal or high Variable
Purulent meningitis (bacterial)5 community-acquired 200–20,000 (0.2–20 × 109/L) polymorphonuclear neutrophils Low (< 45) High (> 50) Markedly elevated
Spirochetal meningitis 100–1000 (0.1–1.0 × 109/L), mostly lymphocytes3 Normal High (> 50) Normal to slightly elevated

1Cerebrospinal fluid glucose must be considered in relation to blood glucose level. Normally, cerebrospinal fluid glucose is 20–30 mg/dL lower than blood glucose, or 50–70% of the normal value of blood glucose.

2Viral isolation from cerebrospinal fluid early; antibody titer rise in paired specimens of serum; polymerase chain reaction for herpesvirus.

3Polymorphonuclear neutrophils may predominate early.

4May occur in mastoiditis, brain abscess, epidural abscess, sinusitis, septic thrombus, brain tumor. Cerebrospinal fluid culture results usually negative.

5Organisms in smear or culture of cerebrospinal fluid; counterimmunoelectrophoresis or latex agglutination may be diagnostic.

eFigure 30–2.

Collection of cerebrospinal fluid. (Reproduced, with permission, from Chesnutt MS et al. Office & Bedside Procedures. Copyright © 1992 by The McGraw-Hill Companies, Inc.)

An illustration shows a patient lying on their side. A gloved hand inserts a needle in the lower spine and unscrews a storage bottle.
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A. Purulent Meningitis

Patients with bacterial meningitis usually seek medical attention within hours or 1–2 days after onset of symptoms. The organisms responsible depend primarily on the age of the patient as summarized in Table 30–2. The diagnosis is usually based on the Gram-stained smear (positive in 60–90%) or culture (positive in over 90%) of the cerebrospinal fluid.

Table 30–2.Initial antimicrobial therapy for purulent meningitis of unknown cause.
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Table ...

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