The initial management of a suspected CNS infection – Step 2 CK exam

by / Friday, 25 June 2010 / Published in Internal Medicine

Often when a CNS infection is suspected, a head CT should be performed before the LP.

This is the case in the following circumstances:

  • A history of CSN disease
  • Focal neurological deficits
  • Presence of papilledema
  • Seizures
  • Altered consciousness
  • Significant delay in ability to perform LP

** If these are present, get blood cultures and start empiric antibiotics before ordering CT.


  • Getting CSF is the most accurate test for bacteria meningitis, but cannot wait for culture to start therapy.
  • Gram stain: only 50% sensitive, thus if (-) cannot exclude anything. Is highly specific though, so if (+) it is likely to be bacteria meningitis.  Ie. Good spec bad sensitivity
  • Gram (+) diplococci: pneumococcus
  • Gram (+) bacilli: listeria
  • Gram (-) diplococci: neisseria
  • Gram (-) pleomorphic, coccobacillary organisms: hemophilus

Protein: An elevated protein level in CSF is of marginal diagnostic benefit.  Elevated protein is non-specific because any form of CSN infection can elevate the CSF protein.  However, a normal CSF protein excludes bacterial meningitis.

Glucose: Levels below 60% of serum levels is consistent w/ bacterial meningitis

Cell count: This is best initial test for the diagnosis of meningitis.  If thousands of PMN’s are present start IV ceftriaxone, vancomycin, and steroids.  Thousand of PMN’s is bacterial meningitis until proven otherwise.

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