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Key Features

Essentials of Diagnosis

  • Central nervous system (CNS) infection is a medical emergency

  • Immediate diagnostic steps must be instituted to establish the specific cause

General Considerations

  • Infections can be caused by almost any infectious agent, including

    • Bacteria

    • Mycobacteria

    • Fungi

    • Spirochetes

    • Protozoa

    • Helminths

    • Viruses

ETIOLOGIC CLASSIFICATION

  • CNS infections can be divided into several categories that are readily distinguished by cerebrospinal fluid (CSF) examination as the first step toward diagnosis (Table 30–1)

  • Purulent meningitis

    • 18–50 years: Streptococcus pneumoniae, Neisseria meningitidis

    • > 50 years: S pneumoniae, N meningitidis, Listeria monocytogenes, gram-negative bacilli

    • Impaired cellular immunity: L monocytogenes, gram-negative bacilli, S pneumoniae

    • Postsurgical or posttraumatic: Staphylococcus aureus, S pneumoniae, gram-negative bacilli

  • Chronic meningitis

    • Mycobacterium tuberculosis or atypical mycobacteria

    • Fungi: Cryptococcus, Coccidioides, Histoplasma

    • Spirochetes: Treponema pallidum, Borrelia burgdorferi

    • Other: brucellosis, HIV infection

  • Aseptic meningitis

    • Mumps

    • Herpes simplex virus, coxsackievirus, echoviruses

    • Infectious mononucleosis

    • Leptospirosis, syphilis, Lyme disease

    • Drug-induced aseptic meningitis (eg, from nonsteroidal anti-inflammatory agents, sulfonamides and certain monoclonal antibodies)

  • Encephalitis

  • Partially treated bacterial meningitis

  • Neighborhood reaction

  • Noninfectious meningeal irritation

  • Brain abscess

  • Health care–associated meningitis

    • May result from invasive neurosurgical procedures (eg, craniotomy, internal or external ventricular catheters, external lumbar catheters), complicated head trauma, or hospital-acquired bloodstream infections

    • Outbreaks have been associated with contaminated epidural or paraspinal corticosteroid injections

    • Microbiology is generally distinct from community-acquired meningitis, with the following playing a larger role:

      • Gram-negative organisms (eg, Pseudomonas), S aureus, and coagulase-negative staphylococci

      • Mold and fungi (Exserohilum rostratum and Aspergillus fumigatus) in outbreaks associated with contaminated corticosteroids

Table 30–1.Typical cerebrospinal fluid findings in various central nervous system diseases.

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