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Infection can affect the function of the nervous system by damaging the brain or its lining (meningoencephalitis, abscess, subdural empyema), spinal cord (myelitis, cord compression), lumbosacral plexus, muscle, and nerve. At least 1% of hospital admissions relate to infection of the central nervous system (CNS).
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ESSENTIALS OF DIAGNOSIS
Acute onset of headache, stiff neck, confusion, lethargy or coma, and fever
Petechial rash implicates meningococcal cause
Most likely organism depends on patient’s age, immune status, including vaccination history, and special risk factors of exposure, surgeries, and drug use
Cerebrospinal fluid (CSF) analysis showing high opening pressure, decreased glucose, (normal 0.6 CSF/serum), more than 10 white blood cells (WBCs)/µL (predominantly polymorphonuclear neutrophils), and increased protein
Encapsulated organisms visualized by Gram stain
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General Considerations
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Bacterial meningitis in adults has an incidence rate of 4–6 cases per 100,000 persons in the United States and 50 cases per 100,000 in developing countries. It is associated with morbidity in up to 50%, the most serious being cerebral edema with depression of consciousness and septic shock; mortality rates up to 20% have been reported. Sequelae in survivors include stroke in 15%, cognitive impairment in up to 25% and deafness in 10–20%. Urgent commencement of treatment is of the essence; when antibiotics are initiated after 6 hours from arrival for care (generally due to delay in performing lumbar puncture) the prognosis is much worse. Therefore, appropriate management of suspected meningitis is administration of empiric antibiotics to be given after blood culture, even before obtaining CSF. The CSF profile (glucose, protein, CSF white blood cell and red blood cell count and type of cells) supports evidence for bacterial or mycobacterial, viral, fungal, or aseptic etiology. Molecular rapid diagnostic testing (mRDT), including polymerase chain reaction (PCR) and other techniques, reduces the time to identification of the pathogenic organism, but cultures are still necessary to direct appropriate therapy. In the absence of mRDT while awaiting culture results, clinical clues can be used to predict the bacteria based on the patient’s age, history of vaccination against common agents (eg, Haemophilus influenzae, Streptococcus pneumoniae, or Neisseria meningitidis), immune state (alcoholic, postsplenectomy, steroid-dependent, HIV), epidemic or close contact exposure, recent dental or surgical procedure, or other special circumstances. Common organisms and their treatment are reviewed in Tables 26–1 and 26–2.
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