Pathogenesis of central nervous system tuberculosis.

Central Nervous System (CNS) tuberculosis is a serious, often fatal form of tuberculosis, predominantly affecting young children. HIV co-infection and drug resistant strains of Mycobacterium tuberculosis are making the diagnosis and treatment of CNS tuberculosis more complicated. Current concepts about the pathogenesis of CNS tuberculosis are based on necropsy studies done in 1933, which suggest that tuberculous meningitis develops subsequent to the rupture into the cerebrospinal fluid of tuberculomas that form around M. tuberculosis deposited in the brain parenchyma and meninges during the initial hematogenous dissemination. Foreign antigens including pathogens deposited in the brain parenchyma are not detected efficiently by the immune system in the CNS. These experimental data may explain the clinical observation of delayed "paradoxical" enlargement or development of intracranial tuberculomas, observed several weeks to months in patients receiving anti-tuberculous therapy. Since severe sequelae are observed even when CNS tuberculosis is treated effectively, it is important to develop preventive strategies for this disease. Recent data utilizing animal models suggests that, in addition to host factors, M. tuberculosis genes and their encoded proteins may contribute specifically to bacterial invasion and survival in the CNS. Understanding how these microbial factors affect CNS disease would be essential to developing such preventive strategies.