Acute Meningitis

Acute meningitis is a neurological emergency. Clinical evaluation alone cannot accurately determine the cause of meningitis; lumbar puncture (LP) is essential and should be performed without delay. Empiric treatment should be started while waiting to confirm a pathogen, as earlier treatment reduces mortality and sequelae, particularly in bacterial meningitis.

A.

Meningitis should be suspected in patients exhibiting any two of the following symptoms: decreased level of consciousness, headache, neck stiffness, fever, or unexplained seizures. Immunocompromised patients may present without neck rigidity or fever, so a high level of suspicion must be maintained. Emesis is an often-overlooked symptom that tends to accompany bacterial meningitis.
B.

Obtain a detailed medical history including travel and exposures. Human immunodeficiency virus (HIV) or immunocompromised status must also be ascertained as they predispose to opportunistic infections such as cryptococcosis and tuberculosis. A comprehensive medication history is also indicated. Commonly used medications, including nonsteroidal antiinflammatory drugs, intravenous immunoglobulin, penicillins, and cephalosporins, can cause drug-induced aseptic meningitis. Recent antibiotic use should be assessed, as this may confound the results of cerebrospinal fluid cultures.
C.

Prompt empiric treatment is imperative, as delay to antibiotic initiation worsens outcomes and increases mortality. Do not delay medications until after LP has been performed.
- 1.
  
  Empiric acyclovir until herpes simplex virus (HSV) encephalitis can be excluded. Dosage is 10–15 mg/kg every 8 hours.
- 2.
  
  Empiric therapy for acute bacterial meningitis
  - a.
    
    Community acquired—vancomycin + third-generation cephalosporin.
  - b.
    
    Recent neurosurgical instrumentation—requires coverage for Pseudomonas . Use vancomycin + fourth-generation cephalosporin or carbapenem.
  - c.
    
    Immunocompromised, elderly, or young—requires coverage for Listeria . Add ampicillin.
  - d.
    
    Concurrent otitis, mastoiditis or sinusitis—add metronidazole.
  - e.
    
    Empiric steroids may improve mortality and outcome in adults with Streptococcus pneumoniae and Neisseria meningitidis infections, and reduce delayed hearing loss in children with Haemophilus influenzae infections. It is therefore reasonable to give steroids to patients with suspected bacterial meningitis due to these organisms (dexamethasone, 0.15 mg/kg up to 10 mg every 6 hours in developed countries, 0.4 mg/kg every 12 hours in developing countries, give first dose 15 minutes prior to starting antibiotics). The benefit of steroids is equivocal in developing countries where rates of HIV infection are high. Steroids should be stopped at 4 days, or immediately after disproving the mentioned organisms.
D.

Obtain head computed tomography prior to LP in immunocompromised patients or those with signs of increased intracranial pressure, focal neurologic findings, or seizures. In the absence of these risk factors, LP may be performed without prior imaging.
E.

LP should be performed without delay. Include opening and closing pressures, cell counts, protein and glucose measurement, Gram stain and culture, and cryptococcal antigen testing. It is useful to save cerebrospinal fluid for additional specific testing once the cell counts are available, as this may help focus diagnostic testing. Common tests to consider include polymerase chain reaction (PCR) for herpes simplex virus (HSV), varicella zoster virus (VZV), West Nile disease, Epstein-Barr virus, and enterovirus, as well as Lyme disease (if in an endemic region) and syphilis (Venereal Disease Research Lab, VDRL) testing. The latter are generally tested in both blood and cerebrospinal fluid (CSF). A variety of less common infectious organisms can be tested for in the proper clinical context. Low CSF glucose levels should raise suspicion for fungal or tuberculous meningitis. Neutrophilic-predominant pleocytosis suggests bacterial meningitis, while a lymphocytic predominance suggests viral meningitis (though the latter can be seen in early bacterial meningitis at times).
F.

Further therapy should be guided by results of gram stain, culture, and other specific diagnostic testing. If cultures are negative but suspicion for bacterial meningitis remains, PCR and/or proteomics-based assays may aid in pathogen identification. If viral meningitis continues to be of concern, echovirus PCR from stool or throat samples can be of higher yield than that from CSF.