Clinical course
Response to antimicrobial therapy is the most important determinant of additional clinical steps. If there is decline in neurologic status over the next 48 hours, CNS imaging is essential to evaluate for evidence of increase in ICP that would suggest meningoencephalitis. This may be the course of a bacterial process, or it may be suggestive of an alternative etiology if no bacterial infection has yet been identified. Increasing ICP in the setting of bacterial meningitis is difficult to manage clinically, but monitoring in the ICU is necessary. A lumbar drain or ventriculostomy has been lifesaving in select cases.
Rapid deterioration that continues to frank coma or intractable seizures may indicate subdural empyema. This can be seen in the setting of otitis media, mastoiditis, or sinusitis and is best diagnosed with MRI. Surgical drainage by craniotomy is the treatment of choice.
Cranial-nerve palsies may also occur as a result of increased ICP or local meningeal inflammation. Eighth-nerve palsies are the most common permanent neurologic sequelae in pneumococcal meningitis (seen in up to 14% of cases), but their incidence can be reduced with the appropriate use of corticosteroids. Cochlear implants are usually required once the infection has been cleared.
Finally, if CNS imaging is unremarkable but the patient does not improve or demonstrates clinical deterioration, repeat LP may help to identify drug-resistant pneumococci. This is especially important in areas where penicillin-resistant organisms are endemic.
Once the patient has been stabilized and the pathogen has been isolated, therapy is narrowed to the appropriate agent, which is always administered IV because of the high doses necessary for CSF penetration. Cases attributable to meningococcus or Hemophilus influenzae can be treated for as few as seven days. Pneumococcal meningitis requires 14 days of parenteral therapy. The management of other etiologies of bacterial meningitis should be guided after consultation with a specialist.
Closing thoughts
Bacterial meningitis is a rare but serious infection with potentially devastating consequences. Diagnosis should be made using available bedside techniques as well as laboratory and imaging modalities. Antimicrobial therapy should be initially broad-based with the addition of corticosteroids to reduce morbidity and mortality. Rapid diagnosis can be lifesaving if treatment begins promptly.
