The common neurologic manifestations of bacterial meningitis differ by age group.
|Age group||Neurologic manifestations|
Analysis of the cerebrospinal fluid (CSF) is the main test used in the diagnosis of acute bacterial meningitis. Other tests serve only as adjuncts to CSF analysis, but they can provide useful information about neurologic and systemic complications, including seizures.
The decision to perform a lumbar puncture (LP) is based on clinical presentation (i.e., meningitic signs). When the clinical threshold for LP has been reached, the clinician must first confirm that no focal intracranial mass lesion exists, before LP is performed. A mass lesion such as a tumor, abscess, or subdural empyema will increase intracranial pressure, which might predispose to brain herniation after LP. This precaution is especially relevant when the clinical presentation includes a seizure, particularly a seizure of focal onset. If history and neurologic examination (e.g., papilledema) suggest the existence of such a mass lesion, then LP must be delayed until neuroimaging is performed. If the need for neuroimaging imposes a significant treatment delay, then antimicrobial therapy must be started empirically.
Following is the typical CSF profile of bacterial meningitis:
|Opening pressure||>180 cm H2O|
|Cerebrospinal fluid: serum to glucose ratio||<0.31|
|Red blood cell||Usually 0|
|White blood cell||>10 to <10,000/mm2 (neutrophil predominance)|
|Gram’s stain||Positive in >70% of cases|
|Culture||Species-specific positive in 70–90% of untreated cases|
During acute bacterial meningitis, computed tomography (CT) can be normal or can demonstrate meningeal or ependymal enhancement, or both. It also may show widening of cortical sulci, basal cistern, or both, secondary to the accumulation of purulent exudate or bacterial meningitic complications (e.g., subdural effusion or empyema and diffuse cerebral edema). Development of a seizure (or focal neurologic signs) during meningitis is an additional indication for CT, besides the initial pre-LP screening.
Magnetic resonance imaging (MRI) is generally more useful than CT. MRI better images subdural effusions and empyemas, cortical infarctions, and the extent of leptomeningeal enhancement.
A full range of EEG abnormalities can be seen in the context of acute bacterial meningitis, from nonspecific slowing to status epilepticus. A corresponding variety of EEG findings can occur as part of the neurologic sequelae of bacterial meningitis.
Reviewed and revised March 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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