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.
Infections of the CNS can be caused by almost any infectious agent, including bacteria, mycobacteria, fungi, spirochetes, protozoa, helminths, and viruses.
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). ||Download (.pdf) 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 |
Collection of cerebrospinal fluid. (Reproduced, with permission, from Chesnutt MS et al. Office & Bedside Procedures. Copyright © 1992 by The McGraw-Hill Companies, Inc.)
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.