ACUTE
BACTERIAL MENINGITIS
Potentially
severe / fatal inflammation of meninges due to bacterial invasion that can
occur in any age group from neonates to very elderly (most common in teenage
years)
History:
Classic
Triad (each present
in > 80% but rarely one in isolation) of:
1. Fever
- absent or even low in elderly, immunocompromised or already on antibiotics
2. Headache - severe w/ N+V,
photophobia / Neck Stiffness
3. Altered
Mental Status - agitation, lethargy, confusion or stupor (coma in 10%)
Suspect
meningitis in the elderly with confusion even without headache or meningismus
Onset may
be acute and fulminant (25%), subacute over days (50%) or over 1-2 weeks
Additional
features may include:
- Hx of
preceding URTI infection (or pneumonia, sinusitis, otitis media)
-
Confusion with lethargy or agitation (rarely comatose early on unless
post-ictal)
- Double
vision or focal neurological deficits
-
Seizures (< 20%); more common in children
Be sure
to ask about risk factors for meningitis (and think about TB / fungal):
- Risk
factors for immunocompromised state (transplantation, HIV, DM, malignancy,
steroid Rx)
-
Immunodeficiency (agammaglobulinemia, complement deficiency)
- Splenectomy or functional asplenia (eg.
sickle cell disease)
- Alcohol
abuse
- Recent
neurosurgical procedure or head injury / skull fracture / presence of CSF shunt
-
Exposure to others / recent travel / unpasteurized milk intake (listeria)
Ask about
recent antibiotic use (may reduce the yield of bacterial cultures and affect
CSF results)
Examination:
1. Vitals:
temperature but also HR / BP / O2 Saturation
- follow
for signs of septic shock, ARDS and DIC
2. LOC:
normal to comatose (usually lethargic or agitated but rousable)
3. Fundi:
papilledema in < 10% on arrival (its absence does not rule out increased
ICP)
- if
present, consider septic sinus thrombosis, abscess, empyema or hydrocephalus
4. CN
palsies (esp ocular motor, facial, and auditory - remember VI can be false-localizing)
5.
Meningismus - check for nuchal rigidity with passive neck flexion (gives
'involuntary' resistance)
- also
Brudzinski sign (hip & knee flexion with neck movement) & Kernig sign
(raise head when extend knee with hip flexed) => signs of irritated meninges
6.
Hemiparesis
7. Rash:
petechial or purpuric rash (not only in meningococal but also pneumococcal
bacteremia)
Diagnosis:
Meningitis
is defined by the presence of WBCs in CSF (see Lumbar Puncture review)
-
bacterial meningitis usually has a specific pattern in combination with a
positive CSF culture
WBC
Count: usually > 1,000 cells / microliter (predominant neutrophils)
(NB:
correct for traumatic RBCs in CSF using 1:700 ratio of excess WBCs to extra
RBCs)
Protein:
elevated (1-10 g/L)
Glucose:
< 40% of concurrent serum glucose (often absolute CSF glucose < 2.0)
(NB: low
glucose seen in bacterial, fungal, tuberculous and carcinomatous meningitis from
impaired glucose transport into CSF)
Opening
pressure: elevated (> 30 cm H20)
Gram
Stain: allows rapid identification of pathogenic organisms
-
positive in 60-90% of bacterial meningitis
Culture
provides definitive diagnosis as well as identificaiton of pathogenic organism
and antibiotic susceptibilities
- also
send blood cultures which are positive in 50%
PCR for
microbial DNA may become sensitive and specific method for bacterial
identification
- not
rapid enough to affect immediate management
Differentiating
Bacterial from Viral or Aseptic Meningitis:
Features
of viral meningitis:
-
lymphocytic predominance (but may see neutrophils if CSF sampled early in
course - up to 48hrs)
- glucose
not reduced
- total
cell count usually 50-500
-
bacterial cultures ultimately will be negative (hence 'aseptic' meningitis)
- WBC
aggregation testing may prove useful test (much higher in bacterial vs viral)
making prolonged hospitalization and antibiotic Rx awaiting final cultures less
necessary
- viral
culture in CSF positive in only small proportion
CT
Scanning before Lumbar Puncture in Suspected Meningitis:
The
absence of all these features makes a signficant lesion precluding LP very
unlikely:
- Age
> 60 yrs
-
Immunocompromised state
- Hx of
CNS disease
- Seizure
within one week of presentation
-
Abnormal LOC
- Unable
to answer two questions correctly or follow two commands
-
Abnormal neurologic examination (VFD, facial palsy, drift, aphasia)
Empiric
Antibiotics:
Cefotaxime
2g IV q4hrs
add
Vancomycin 1-2 g IV q8-12 hrs in all patients (till possibility of
Penicillin-resistant Strep pneumoniae has been ruled out)
add
Ampicllin 2g IV q4hrs in elderly or immunocompromised patients (for Listeria
infections)
- for
patients with serious penicillin allergies, Meropenem 1-2g IV q8hrs as
alternative
Ceftazidime
(2g IV q8hr) + Vancomycin for neurosurgical patients, those with shunts or CSF
leaks
May
consider adjunctive Acyclovir (10 mg/kg IV q8hrs if normal renal function)
- if any
suspicion of encephalitis (seizures, focal deficits, lymphocytic pleocytosis)
Use of
adjunctive corticosteroids:
- prior
to or along with initial antibiotics, administer Dexamethasone 10 mg IV
for suspected bacterial meningitis (based on cloudy CSF, CSF WBC counts >
1000 or + Gram stain)
- continue
10 mg IV q6hr x 4 days
Microbiology:
1.
Streptococcus pneumoniae (pneumococcal still most common)
2.
Neisseria meningitidis (meningoccocal esp in teens and young adults)
3.
Haemophilus influenzae (dramatic decline in children with routine Hib vaccination)
4.
Listeria: neonates, elderly or immunocompromised (may have lower cell count
with more lymphs)
4. Staph
aureus & Gram negative organisms: head trauma / neurosurgery patients
By age
group: (relative percentages are approximate)
Neonates:
- Group B
Streptococcus (esp early cases) - 75%
- Gram
negatives (esp E. coli) - 20%
- others
incl. Listeria
Infants
& Children:
- Strep.
pneumoniae - 40%
- Neisseria
meningitidis - 40%
- Haemophilus
influenzae - now rare
- others
incl. Group B Strep
Adults:
- as with
infants & children (except Group B Strep)
Elderly:
- Strep.
pneumoniae (most common) - 50%
- Gram
negatives (incl. E. coli) - 25%
-
Listeria - < 10%
Prognostic
Factors:
1. Age
2. Level
of Consciousness (50% mortality if unresponsive or minimally responsive on
admission)
3.
Seizures early in course
4. Strep.
pneumoniae meningitis
5. CSF
results (lower glucose & WBC counts, higher protein)
Common
Complications:
1.
Hydrocephalus
2.
Seizures
3. SIADH
4. Subdural
effusions & empyema
5. Septic
sinus or cortical
vein thrombosis
6.
Arterial ischemia / infarction (inflammatory vasculitis)
7. CN
Palsies (esp deafness)
8. Septic
shock / multi-organ failure from bacteremia (esp meningococcus &
pneumococcus)
- risk of
adrenal hemorrhage with hypo-adrenalism (Waterhouse-Friderichsen syndrome)
Isolation
& Contact Prophylaxis:
-
generally isolate cases of bacterial meningitis for up to 48 hours of
appropriate antibiotics
- concern
is to reduce transmission of meningococcal infections
- can be
taken out of isolation after this time or if alternative pathogen identified
-
department of health should be notified of pathogens in pyogenic meningitis
Close
contacts (family members, partners, co-workers or school children) should
receive prophylaxis if meningococcal or haemophilus influenzae type B (if not
vaccinated):
-
rifampin 600 mg
-
ciprofloxacin 500 mg
References:
De Gans
J, Van De Beek D, et al. Dexamethasone
in adults with bacterial meningitis. N
Engl J Med 2002; 347: 1549-56.
Hasbun R,
Abrahams J, et al. Computed tomography
of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med 2001; 345: 1727-33.
Kaplan
SL. Bacterial meningitis: clinical
presentation, diagnostic, and prognostic factors of bacterial meningitis. Inf Dis Clin N Am 1999; 13(3): 579-94.
Last update: 2003-06-08
Reviewed by: pending review
Neurological
Medicine Pocketbook
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