Tuberculous meningitis: correlation of therapeutic results with the pathogenesis and pathologic changes. I. General considerations and pathogenesis

Invasion of the central nervous system by intracellular bacteria

Infection of the central nervous system (CNS) is a severe and frequently fatal event during the course of many diseases caused by microbes with predominantly intracellular life cycles. Examples of these include the facultative intracellular bacteria Listeria monocytogenes, Mycobacterium tuberculosis, and Brucella and Salmonella spp. and obligate intracellular microbes of the Rickettsiaceae family and Tropheryma whipplei. Unfortunately, the mechanisms used by intracellular bacterial pathogens to enter the CNS are less well known than those used by bacterial pathogens with an extracellular life cycle. The goal of this review is to elaborate on the means by which intracellular bacterial pathogens establish infection within the CNS. This review encompasses the clinical and pathological findings that pertain to the CNS infection in humans and includes experimental data from animal models that illuminate how these microbes enter the CNS. Recent experimental data showing that L. monocytogenes can invade the CNS by more than one mechanism make it a useful model for discussing the various routes for neuroinvasion used by intracellular bacterial pathogens.

CNS tuberculosis

Tuberculous meningitis is a rare, treatable neurologic disorder, in which early recognition is paramount because outcome depends greatly on the speed with which therapy is initiated. Patients with meningitis and CSF findings of low glucose, elevated protein and pleocytosis with evidence of tuberculosis elsewhere in the body (chest radiographs, positive tuberculin skin test), or a history of exposure to tuberculosis should be treated immediately with antituberculous medication. When the diagnosis remains uncertain, serial examination of the CSF for tuberculous organisms will often yield positive results. The CT scan may show hydrocephalus, a basilar arachnoiditis, or intraparenchymal lesions: tuberculomas. Hydrocephalus may respond to early shunting. Tuberculomas are best treated medically. Therapy should include INH and rifampin; ethambutol and pyrazinamide are suggested for the first 2 months of therapy. Steroids may be useful in diminishing the inflammatory response when altered consciousness or focal neurologic signs are present.