Managing Meningitis 

This topic was discussed in noon rounds today as part of our emergency lecture series. 

Bacterial meningitis is a medical emergency - data from a retrospective study in 2008 from the Journal of Infection showed that unfavourable outcomes increase by 30% for every one hour delay in treatment. From med school and residency, we know that it requires antibiotics (and maybe steroids) targeted at the appropriate organisms, we know that some people may need a CT scan, and we know that it is diagnosed with an LP. The order in which we do all of this, or if we need to do them all is sometimes unclear.

Firstly, is there physical exam findings that can help rule in our out? From the 1990 JAMA RCE article "Does this adult patient have acute meningitis?" we know that the absence of all 3 of fever, mental status changes, AND neck stiffness is quite sensitive in ruling out meningitis. Also a negative jolt accentuation has good sensitivity as well. There is no physical finding that is diagnostic and definitive diagnosis requires further testing.

Secondly, what about a CT head before an LP? Practice guidelines, including those from the IDSA, would suggest that select few patients can safely undergo LP without prior CT. Essentially these are people who lack any features including age > 60, immunocompromise, prior history of CNS infection, recent seizure, objective focal neurologic findings.

If you do send someone for a CT scan, they should be started on therapy as time will add up as you await transport, the scan, and the interpretation. This invariably leads to concern that we will 'sterilize' the CSF and lose the ability to make a definitive diagnosis.

We now know that the biochemical and hematologic abnormalities persist despite antibiotic therapy, at least within the first 24 hours, and possibly longer. This was first answered in 1990 when a noninferiority study comparing "the new" Ceftriaxone to Cefuroxime for the treatment of bacterial meningitis in pedatric patients. They performed LP's on presentation and 24 hours post antibiotics. While the rate of positive gram stains predictably went down, the other parameters such as WBC, protein, glucose, remained unchanged, and so could aid in diagnosis. 

The landmark NEJM study by deGans et. al in 2002 showed that dexamethasone improved outcomes and mortality for S.pneumo meninigitis, but given the low numbers, the same could not definitively be said for other pathogens.

Bottom line, as per guidelines, 

If bacterial meningitis is suspected and the patient does not have indications for a CT, 

then the order should be blood cultures, LP, empiric therapy.

If a CT is indicated, 

then the order should be blood cultures, empiric therapy before sending to CT, if CT negative, then LP.

Click here for the IDSA guidelines for bacterial meningitis

And here for a great summary on key points of bacterial meninigitis from the CMAJ.