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Chapter 52. Bacterial Infections of the Central Nervous System

Allan R. Tunkel; W. Michael Scheld

  • More than 80% of adults with bacterial meningitis present clinically with fever, headache, meningismus, and signs of cerebral dysfunction; elderly patients, however, may present with insidious disease manifested only by lethargy or obtundation, variable signs of meningeal irritation, and no fever.
  • Occasionally, a patient with acute bacterial meningitis has a low cerebrospinal fluid (CSF) white cell count despite high bacterial concentrations in CSF; therefore, a Gram stain and culture should be performed on every CSF specimen, even if the cell count is normal.
  • Neuroimaging techniques have little role in the diagnosis of acute bacterial meningitis. However, computed tomography (CT) should be performed before lumbar puncture when a space-occupying lesion of the central nervous system (CNS) is suspected. Clinical features at baseline associated with an abnormal CT image (in patients with suspected meningitis) are age of at least 60 years, immunocompromise, a history of CNS disease, a history of seizure within 1 week before presentation, and specific neurologic abnormalities.
  • Empirical antimicrobial therapy, based on the patient's age and underlying disease status, should be initiated as soon as possible in patients with presumed bacterial meningitis; therapy should never be delayed while diagnostic tests such as CT are awaited.
  • Adjunctive dexamethasone therapy has been shown to decrease the morbidity rate in infants and children with acute Haemophilus influenzae type b meningitis and, if commenced with or before antimicrobial therapy, is also beneficial for pneumococcal meningitis in childhood. A recent study has associated adjunctive dexamethasone with decreased morbidity and mortality rates in adults with pneumococcal meningitis when administered before the first dose of antimicrobial therapy.
  • Only about 50% of patients with brain abscess present with the classic triad of fever, headache, and focal neurologic deficit; the clinical presentation of brain abscess in immunosuppressed patients may be masked by the diminished inflammatory response.
  • The diagnosis of brain abscess has been revolutionized by the development of CT; magnetic resonance imaging may offer advantages over CT in the early detection of cerebritis, cerebral edema, and satellite lesions.
  • Aspiration of brain abscess under stereotaxic CT guidance is useful for microbiologic diagnosis, drainage, and relief of increased intracranial pressure.
  • A short course of corticosteroids may be useful in patients with brain abscess who have deteriorating neurologic status and increased intracranial pressure.
  • Cranial subdural empyema should be suspected in patients with headache, vomiting, fever, change in mental status, and rapid progression of focal neurologic signs.
  • Spinal epidural abscess may develop acutely or chronically, with symptoms and signs of focal vertebral pain, nerve root pain, motor or sensory defects, and paralysis; the transition to paralysis may be rapid, indicating the need for emergent evaluation, diagnosis, and treatment.
  • Surgical therapy is essential for the management of subdural empyema because antibiotics do not reliably sterilize these lesions.
  • Rapid surgical decompression should be performed in patients with spinal epidural abscess who have increasing neurologic deficit, peristent severe pain, or increasing temperature or peripheral white blood cell count.
  • Lateral gaze palsy may be an early clue to the diagnosis of cavernous sinus ...

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