from Southeast Asia, Africa, and eastern Europe, and in the immunocompromised, particu-
larly among patients with HIV infection. TB, caused byMycobacterium tuberculosis, is spread
primarily by airborne droplets, initially causing pulmonary infection. Although this infection
is typically controlled by cell-mediated immunity, some degree of hematogenous dissem-
ination occurs frequently. Bacilli can seed the CNS where tuberculomas most commonly occur
along the meninges, but can occur at typical intraparenchymal sites of hematogenously
disseminated infection such as the cortical-subcortical gray-white junction. At some point long
after initial infection, a tuberculoma may rupture into the subarachnoid space causing
meningitis. This meningitis tends to involve the meninges at the base of the brain (regardless of
where the tuberculoma was), where involvement of the cranial nerves and blood vessels that
pass through the subarachnoid space is commonplace. This results in cranial neuropathies,
obstructive hydrocephalus, and strokes (4).
In the absence of obvious chest X-ray findings, diagnosis can be challenging. In a small
percentage of patients, brain imaging will demonstrate thick enhancement of the basilar
meninges. Skin tests are usually but not invariably positive. CSF analysis typically demonstrates
a significant lymphocytic pleocytosis (cell count in the 100’s to 1000’s) with increased protein,
low glucose (sometimes immeasurably so), and elevated adenosine deaminase concentration (5).
The latter, indicative of a vigorous T-cell response, is said to have approximately 90% sensitivityTable 1 Common Etiologic Agents and Diagnostic Approach
Acute Bacterial Meningitis
Brain imaging
Blood cultures
CSF examination
Identify source (skin, sinuses, mastoids, dental, cardiac, other)
Indolent Bacterial
TB
Chest X Ray
Brain MRI with contrast (basal cisterns)
CSF examination
Neuroborreliosis (Lyme disease)
Peripheral blood serologic testing
Consider CSF examination including Lyme ELISA
Neurosyphilis
Serum reaginic and specific serologic testing
CSF reaginic and specific serologic testing
Listeria
Brain MRI with contrast (brainstem)
CSF examination
Mycoplasma
Chest X Ray
Serum cold agglutinins
IgM mycoplasma ELISA
Viral
Herpes simplex
Brain MRI with contrast (frontal and temporal lobes)
CSF with PCR
West Nile virus
Brain MRI with contrast (brainstem)
Serum IgG and IgM specific serologies (acute and convalescent)
CSF serology and PCR
Rabies
Immunofluorescence for virus in skin biopsy
Serology
Saliva PCR
Abbreviations: CSF, cerebrospinal fluid; IgG, immunoglobulin G; IgM,
immunoglobulin M; MRI, magnetic resonance imaging; PCR, polymer-
ase chain reaction; TB, tuberculosis.
156 Halperin