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meningitis

meningitis

introduction

  • bacterial meningitis and meningococcal sepsis are two separate but overlapping entities which often co-exist
  • most cases of bacterial meningitis result from seeding from an episode of bacteraemia with a virulent organism (although in neonates, this may just be from an organism causing a UTI)
  • some cases of bacterial meningitis result from extension of regional infection, such as from V-P shunts, etc.

ED Mx of suspected meningitis

  • high priority triage (eg. triage 2)
  • A,B,C's as usual
  • iv access
  • check BSL
  • bloods for FBE, U&E, blood cultures x2 sets, clotting profile, meningococcal PCR
  • careful iv fluid resuscitation if hypotense as high risk of delayed APO - see sepsis / septicaemia
  • stratify risk (see below) to decide who gets immediate antibiotic Rx, and who gets CT/LP
  • if primarily septicaemic, immediate iv antibiotics DO NOT do LP
  • if primarily meningitis, consider LP before iv antibiotics if not contraindicated (see below) and doesn't delay antibiotics by more than 20-30min.
  • iv dexamethasone 0.15mg/kg to max 10mg qid for 4 days start before or at 1st dose antibiotics, particularly for pneumonococcal cases. Cease if non-bacterial cause identified.
    • reduces mortality, severe hearing loss and long-term neurological sequelae in bacterial cases, esp. if pneumococcal.
  • iv ceftriaxone 50mg/kg to max 2g bd
  • consider iv benzyl penicillin 60mg/kg to max 2.4g 4hrly or ampicillin 2g qid if immunosuppressed or possible Listeria (eg. age < 3 months or age > 55 years)
  • consider adding vancomycin 12.5 mg/kg up to 500 mg IV 6-hrly if Strep. pneumoniae or Staph. aureus are suspected, or neutrophils are in CSF but no organisms seen (and if viral meningitis / meningococcal disease are unlikely).
  • patients with altered mental state should be considered for possible herpetic meningoencephalitis and consideration given to empirical iv antiviral Rx as well such as iv aciclovir
  • infectious disease isolation measures
  • nurse patient at 30deg head up if altered mental state
  • if meningococcal disease, it is a notifiable disease and will need contact tracing and chemoprophylaxis for contacts.

high risk features that mandate immediate iv antibiotic Rx

  • presence of meningococcal rash
  • fever, headache, photophobia and objective neck stiffness (not just soreness)
  • fever with seizures (excluding typical febrile convulsions in young children)
  • fever with altered mental state (excluding post-ictal following a typical febrile convulsion or other obvious cause for the mental state change)
  • sick looking febrile neonate or infant
  • rectal temp > 38deg C in a neonate (aged < 1 month or weighing < 3.5kg)1)
  • NB. at risk patients with known spinal abnormalities such as spina bifida or V-P shunts should have early neurosurgical consults

moderate risk features that suggest an LP may be warranted

  • febrile neonate or infant
  • fever, headache, with photophobia &/or neck soreness with no other focus of infection evident
  • fever, headache and already on antibiotics

lumbar puncture

  • most patients require the diagnosis to be confirmed by lumbar puncture (LP) as confirmation will not only aid diagnosis but assist in determining duration and type of ongoing antibiotic Rx.
  • patients with atypical presentations in whom tuberculosis is possible, should be considered for 10ml CSF sent for TB cultures in addition to usual CSF studies.
  • unless the risk of an intracranial mass lesion (eg. abscess, subdural empyema) is very low (eg. previously well young adult or child with illness < 24hrs), a CT brain is usually recommended prior to performing a lumbar puncture (LP).

contraindications to LP

  • shock
  • widespread rash
  • evidence of coagulopathy
  • drowsiness / impaired consciousness
  • signs of raised ICP (bradycardia, hypertension, papilloedema, periodic breathing)
  • focal neurology
  • mass lesion on CT scan
  • possible hydrocephalus on CT scan
  • if LP is contraindicated due to possible raised intracranial pressure, neurosurgical consultation may be indicated to consider a diagnostic ventricular tap.

the diagnostic dilemma

  • meningitis is one of the main dilemmas for the ED physician
  • missing or delaying Rx for a case may have fatal consequences
  • the gold standard for diagnosis involves CT brain and lumbar puncture (LP) - both of which are resource-intense, costly and expose the patient to significant risks
  • for every 1 case of meningitis, there may be 1,000 cases of fever and headache - you can't be doing an LP on them all!
    • 95% of adult patients with meningitis have at least 2 of fever, headache, neck stiffness and altered mental state - but this does not help us because nearly all influenza patients will have fever and headache.
    • altered mental state is generally a late symptom and is present in about half the patients at presentation, but this means absence of altered mental state is not in itself reassuring.
    • neck stiffness is NOT a reliable sign in young children or the immunocompromised
  • a blood test does not allow the exclusion or the diagnosis of meningitis (excluding PCR but these are not immediately available to alter ED Mx)
  • patients who are already on antibiotics can become a diagnostic nightmare for the ED physician as clinical signs and even CSF findings become less reliable to exclude meningitis.
    • prior antibiotics usually prevent the culture of bacteria from the CSF.
    • antibiotics are unlikely to significantly affect the CSF cell count or biochemistry in samples taken <24 hours after antibiotics.
  • thus one needs to stratify risk to decide who gets immediate antibiotic Rx, and who gets CT/LP, and who can be observed, and who can be safely discharged.
  • furthermore, an LP cannot fully exclude bacterial meningitis on micro findings alone, and thus if one has a high clinical suspicion of bacterial meningitis, the safe option is to treat with appropriate iv antibiotics +/- aciclovir EARLY and continue them irrespective of CSF micro results.

atypical presentations

elderly

  • no fever or meningism signs but just lethargy, obtundation

immunocompromised

  • may have subtle signs

neonates and young infants

  • poor feeding, irritability, vomiting
  • “a sick looking child with a fever has meningitis until proven otherwise”

normal cell counts on CSF

  • this makes diagnosis tough!
  • this is more likely to be the case with patients already on oral antibiotics

References

meningitis.txt · Last modified: 2012/01/16 06:55 by gary