Presents as fever, headache, and meningeal irritation associated with a CSF lymphocytic pleocytosis. Fever may be accompanied by malaise, myalgia, anorexia, nausea and vomiting, abdominal pain, and/or diarrhea. A mild degree of lethargy or drowsiness may occur; however, a more profound alteration in consciousness should prompt consideration of alternative diagnoses, including encephalitis.
Using a variety of diagnostic techniques, including CSF PCR, culture, and serology, a specific viral cause can be found in 60-90% of cases. The most important agents are enteroviruses, VZV, HSV type 2, arboviruses, and HIV (Table 194-4 Viruses Causing Acute Meningitis in North America). The incidence of enteroviral and arboviral infections is greatly increased during the summer.
Most important test is examination of the CSF. The typical profile is a lymphocytic pleocytosis (25-500 cells/µL), a normal or slightly elevated protein concentration (0.2-0.8 g/L [20-80 mg/dL]), a normal glucose concentration, and a normal or mildly elevated opening pressure (100-350 mmH2O). Organisms are not seen on Gram or acid-fast stained smears or india ink preparations of CSF. Rarely, polymorphonuclear leukocytes (PMN) predominate in the first 48 h of illness, especially with echovirus 9, West Nile virus (WNV), eastern equine encephalitis virus, or mumps. The total CSF cell count in viral meningitis is typically 25-500/µL. As a general rule, a lymphocytic pleocytosis with a low glucose concentration should suggest fungal, listerial, or tuberculous meningitis or noninfectious disorders (e.g., sarcoid, neoplastic meningitis).
CSF PCR testing is the procedure of choice for rapid, sensitive, and specific identification of enteroviruses, HSV, EBV, varicella zoster virus (VZV), human herpes virus 6 (HHV-6), and CMV. Attempts should also be made to culture virus from CSF and other sites and body fluids including blood, throat swabs, stool, and urine, although sensitivity of cultures is generally poor. CSF PCR for WNV is not as sensitive as detection of WNV-specific CSF IgM. PCR is also useful in the diagnosis of CNS infection caused by Mycoplasma pneumoniae. PCR of throat washings may assist in diagnosis of enteroviral and mycoplasmal CNS infections and PCR of stool specimens for enteroviral infections. Serologic studies are important for diagnosis of arboviruses such as WNV; however, these are less useful for viruses such as HSV, VZV, CMV, and EBV that have a high seroprevalence in the general population.
Consider bacterial, fungal, tuberculous, spirochetal, and other infectious causes of meningitis; parameningeal infections; partially treated bacterial meningitis; neoplastic meningitis; noninfectious inflammatory diseases including sarcoid and Behçet's disease.
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Viral Meningitis
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