Why should lumbar puncture be performed whenever meningitis is suspected?

Updated: Jul 16, 2019
  • Author: Rodrigo Hasbun, MD, MPH; Chief Editor: Michael Stuart Bronze, MD  more...
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In general, whenever the diagnosis of meningitis is strongly considered, a lumbar puncture should be promptly performed. Examination of the cerebrospinal fluid (CSF) is the cornerstone of the diagnosis. The diagnosis of bacterial meningitis is made by culture of the CSF sample. The opening pressure should be measured and the fluid sent for cell count (and differential count), chemistry (ie, CSF glucose and protein), and microbiology (ie, Gram stain and cultures).

A concern regarding LP is that the lowering of CSF pressure from withdrawal of CSF could precipitate herniation of the brain. Herniation can sometimes occur in acute bacterial meningitis and other CNS infections as the consequence of severe cerebral edema or acute hydrocephalus. Clinically, this is manifested by an altered state of consciousness, abnormalities in pupil reflexes, and decerebrate or decorticate posturing. The incidence of herniation after LP, even in patients with papilledema, is approximately 1%.

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