Acute pyogenic infection of the meninges — neurologic emergency requiring empiric antibiotics within 1 hour.
Also known as: bacterial meningitis, meningococcal meningitis, pneumococcal meningitis, acute meningitis
Overview
Acute pyogenic infection of the leptomeninges and subarachnoid space, characterized by inflammation, neutrophilic CSF pleocytosis, and high morbidity/mortality without prompt antibiotic therapy.
Epidemiology
Incidence in the US ~1-2 per 100,000 adults annually; higher in infants and young children. Vaccination has dramatically reduced Haemophilus influenzae type b and Streptococcus pneumoniae meningitis. Outbreaks of Neisseria meningitidis occur in close-contact settings (college dormitories, military barracks).
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Viral (aseptic) meningitis — Less ill-appearing; lymphocytic CSF, normal glucose, mildly elevated protein, negative gram stain; enterovirus most common
Encephalitis (HSV, arboviral) — Prominent altered mental status, seizures, focal deficits; HSV with temporal lobe involvement on MRI
Subarachnoid hemorrhage — Thunderclap headache; LP with RBCs and xanthochromia; CT head before LP if clinical suspicion
Brain abscess — Focal deficits, ring-enhancing lesion on imaging; LP often contraindicated due to mass effect
Tuberculous meningitis — Subacute course (1-2 weeks), basilar meningitis, cranial nerve palsies, lymphocytic CSF with high protein, very low glucose, AFB smear/PCR/culture
LP CSF studies: opening pressure, cell count and differential, protein, glucose (with simultaneous serum glucose), Gram stain, culture, latex agglutination/multiplex PCR (meningitis/encephalitis panel), HSV PCR, cryptococcal antigen if at risk, AFB stain/culture/PCR if TB suspected, cytology in older patients
Typical bacterial CSF: WBC >1000 (PMN predominant), glucose <40 (or CSF:serum ratio <0.4), protein >200, opening pressure elevated (>250 mm H2O)
Imaging
CT head BEFORE LP only if any of: immunocompromise, history of CNS disease (mass, stroke, focal infection), new seizure within 1 week, papilledema, abnormal level of consciousness, focal neurologic deficit, age >60 — to exclude mass effect and risk of herniation
DO NOT delay antibiotics for imaging or LP — give empiric antibiotics immediately if any delay anticipated
MRI brain if focal findings, suspected complications (abscess, ventriculitis, infarct)
Diagnostic algorithm
Parameter
Bacterial
Viral
Fungal/TB
Normal
Opening pressure (mm H2O)
Elevated (>250)
Normal or mildly elevated
Elevated
70-180
WBC (cells/µL)
>1000 (often 1000-5000)
10-500
100-500
0-5
WBC predominance
Neutrophils (PMN)
Lymphocytes
Lymphocytes
—
Glucose (mg/dL)
Low (<40) or CSF:serum <0.4
Normal
Low
50-80 (~2/3 serum)
Protein (mg/dL)
High (>200)
Mildly elevated (50-150)
Very high (>250)
<45
Gram stain
Often positive
Negative
Negative (AFB/India ink)
Negative
Typical CSF profiles by etiology of meningitis.
Treatment
First-line
Empiric antibiotics within 1 hour of presentation — do not delay for imaging or LP if not immediately available:
Adults 18-50: ceftriaxone 2 g IV q12h + vancomycin 15-20 mg/kg IV q8-12h (covers pneumococcus with ceftriaxone resistance)
Adults >50 or immunocompromised, alcoholic, pregnant: ADD ampicillin 2 g IV q4h to cover Listeria monocytogenes
Children 1 month-18 years: ceftriaxone + vancomycin
Post-neurosurgery/penetrating head trauma: vancomycin + cefepime (or ceftazidime or meropenem) — covers Pseudomonas, MRSA, gram-negatives
Dexamethasone 0.15 mg/kg IV q6h x 4 days, FIRST DOSE 10-20 minutes BEFORE OR WITH first antibiotic dose — reduces mortality and neurologic sequelae (especially hearing loss) in pneumococcal meningitis (de Gans & van de Beek NEJM 2002); continue if pneumococcus confirmed
Acyclovir IV 10 mg/kg q8h if HSV encephalitis cannot be excluded
Second-line / adjunct
Narrow antibiotics once Gram stain/culture/sensitivities return:
S. pneumoniae (gram-positive diplococci): ceftriaxone (continue vancomycin until sensitivities confirm)
N. meningitidis (gram-negative diplococci): ceftriaxone or penicillin G
H. influenzae (gram-negative coccobacilli): ceftriaxone
L. monocytogenes (gram-positive rods): ampicillin ± gentamicin
Group B Streptococcus: penicillin G or ampicillin
Standard duration: meningococcus 7 days, H. influenzae 7-10 days, pneumococcus 10-14 days, GBS 14-21 days, Listeria 21 days, gram-negative bacilli 21 days
Chemoprophylaxis for close contacts of meningococcus: rifampin 600 mg PO BID x 2 days, ciprofloxacin 500 mg PO x 1, or ceftriaxone 250 mg IM x 1 (preferred in pregnancy)
Vaccinate close contacts of vaccine-preventable cases (meningococcal, Hib, pneumococcal); update routine vaccinations in survivors and high-risk patients
Audiology screening on recovery (CN VIII injury, especially pneumococcal)
Complications
Death (mortality ~10-30% adults; up to 50% pneumococcal in elderly)
Sensorineural hearing loss (~10-30%, especially pneumococcal)
Cognitive impairment, memory deficits
Seizure disorder
Cranial nerve palsies
Hydrocephalus, cerebral infarction
Subdural empyema, brain abscess
Septic shock, DIC, adrenal hemorrhage (Waterhouse-Friderichsen with meningococcemia)
Limb necrosis from purpura fulminans
PANCE pearls
Empiric antibiotics within 1 hour. If CT before LP is needed, give blood cultures and antibiotics FIRST.
Add ampicillin for Listeria in patients >50, immunocompromised, alcoholic, or pregnant.
Dexamethasone before/with first antibiotic in suspected pneumococcal meningitis — reduces mortality and hearing loss.
Petechial rash with meningismus = meningococcemia until proven otherwise; isolate, treat, and notify public health.
Vaccination: MenACWY (preteens, college students, military, asplenia, complement deficiency); MenB (high-risk patients and during outbreaks); PCV13/15/20 and PPSV23; Hib in children.
Close contacts of meningococcus require chemoprophylaxis within 24 hours.
In suspected partially treated meningitis (prior antibiotics), Gram stain and culture may be negative — multiplex PCR helpful.
Recurrent meningitis suggests anatomic defect (CSF leak from basilar skull fracture, dermal sinus tract) or complement deficiency.
References
IDSA 2004 — Practice Guidelines for the Management of Bacterial Meningitis (Tunkel et al., Clin Infect Dis 2004; updates pending)
ESCMID 2016 — Diagnosis and Treatment of Acute Community-Acquired Bacterial Meningitis (van de Beek et al., Clin Microbiol Infect 2016)
de Gans NEJM 2002 — Dexamethasone in Adults with Bacterial Meningitis (de Gans & van de Beek, NEJM 2002)
CDC ACIP — ACIP Recommendations for Meningococcal Vaccination
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