Diagnosis
Laboratory studies
Laboratory examination of the cerebrospinal fluid (CSF) usually confirms the presence of meningitis. Typical CSF abnormalities in meningitis include the following:
Increased opening pressure (>180 mm water)
Pleocytosis of polymorphonuclear leukocytes (white blood cell [WBC] counts between 10 and 10,000 cells/µL, predominantly neutrophils)
Decreased glucose concentration (< 45 mg/dL)
Increased protein concentration (>45 mg/dL)
Other laboratory tests can include the following:
Culture of CSF and blood specimens - To identify N meningitidis and the serogroup of meningococci, as well as to determine the bacterium’s susceptibility to antibiotics
Polymerase chain reaction (PCR) assay - For confirmation of the diagnosis
Imaging studies
Computed tomography (CT) scanning - Indications for performing CT scanning prior to lumbar puncture include an altered level of consciousness, papilledema, focal neurologic deficits, and/or focal or generalized seizure activity
Magnetic resonance imaging (MRI) - MRI with contrast is preferred to CT scanning, because MRI better demonstrates meningeal lesions, cerebral edema, and cerebral ischemia
Electroencephalography
An electroencephalogram (EEG) study is sometimes useful to document irritable electrical patterns that may predispose the patient to seizures.
See Workup for more detail.