In classic and fulminant cases of bacterial meningitis, the patient presents with fever, headache, neck stiffness, and altered mental status. Seizures may occur in up to 25% of cases. The presenting picture, however, may be more nonspecific, particularly in the very young and elderly. It is important to inquire about recent antibiotic use, which may cloud the clinical picture in a less florid case. Other key historical data include living conditions (eg, Army barracks, college dormitories), trauma, immunocompetence, immunization status, and recent neurosurgical procedures.
Physical examination should include assessment for meningeal irritation with resistance to passive neck flexion, Brudzinski sign (flexion of hips and knees in response to passive neck flexion), and Kernig sign (contraction of hamstrings in response to knee extension while hip is flexed). Examine the skin for the purpuric rash characteristic of meningococcemia or streptococcemia. Percuss the paranasal sinuses and examine the ears for evidence of primary infection in those sites. Assess for focal neurologic deficits and check the fundi for papilledema, which indicate increased intracranial pressure.
Diagnosis and Differential
When the diagnosis of bacterial meningitis is entertained, treatment should precede diagnostic testing (see ED Care and Disposition Section). Performing a lumbar puncture (LP) is mandatory when bacterial meningitis is suspected. At a minimum, analyze cerebrospinal fluid (CSF) for gram stain and culture, cell count, protein, and glucose. Typical CSF results for meningeal processes are listed in Table 148-1. Additional studies to be considered are latex agglutination or counterimmune electrophoresis for bacterial antigens in potentially partially treated bacterial cases, India ink or serum cryptococcal antigen in immunocompromised patients, acid-fast stain and culture for mycobacteria in tuberculous meningitis, Borrelia antibodies for possible Lyme disease, and viral cultures in suspected viral meningitis. Other laboratory tests should include a complete blood count, blood cultures, coagulation studies, and basic metabolic panel.
Table 148-1 Typical Spinal Fluid Results for Meningeal Processes ||Download (.pdf)
Table 148-1 Typical Spinal Fluid Results for Meningeal Processes
|Opening pressure (< 170 mm cerebrospinal fluid)||> 300 mm||< 300 mm||200 mm||300 mm|
|White blood cell count (< 5 mononuclear)||> 1000/mm3||< 1000/mm3||< 500/mm3||< 500/mm3|
|% Polymorphonuclear cells (0)||> 80%||1% to 50%||1% to 50%||1% to 50%|
|Glucose (> 40 milligrams/dL)||< 40 milligrams/dL||> 40 milligrams/dL||< 40 milligrams/dL||< 40 milligrams/dL|
|Protein (< 50 milligrams/dL)||> 200 milligrams/dL||< 200 milligrams/dL||> 200 milligrams/dL||> 200 milligrams/dL|
|Gram stain (–)||+||–||–||–|
Table 148-2 lists suggested criteria for obtaining head CT prior to LP. In these cases, administer empiric antibiotic therapy before patient transport to CT.
Table 148-2 Some Suggested Criteria for Obtaining Head CT before Lumbar Puncture for Suspected Meningitis