Central nervous system infections in the immunocompromised host.

Central nervous system (CNS) infections in the immunocompromised host are predictable according to the arm of the immune defense which is most defective. A limited number of organisms with a tendency to cause CNS infections will take advantage of the different types of immune defects. Signs and symptoms of CNS infection are often quite subtle in the immunocompromised host because of the diminished inflammatory response. Serologic responses may not be as reliable as in a normal host. Aggressive diagnostic approaches are often necessary, including early brain biopsy and abscess drainage. Aggressive therapy is often also necessary, including multiple potentially toxic antibiotics and devices to deliver them, such as indwelling intraventricular reservoirs. The role of the third generation cephalosporins is still not clear, and certainly they should not be used alone to treat aerobic gram-negative rod meningitis in neutropenic patients. Patients with the acquired immune deficiency syndrome (AIDS) have developed CNS infections with familiar agents producing familiar syndromes. The main CNS infection, however, is a subacute encephalitis and the causative agent remains undocumented.