ABSTRACT
Encephalitis is inflammation of the brain parenchyma. Its cardinal clinical manifestations, occurring singly or in combination, are headache, fever, altered consciousness, and focal neurological deficits. The inflammatory process may be generalized throughout the brain or restricted to focal involvement. It may also involve the meninges. The diversity of clinical features reflects these patterns of involvement and a particular clinical picture is seldom specific to an individual infectious agent. Encephalitis is often an unusual manifestation of a common infection. This leads to variation in the relationship between the systemic infection and the neurological illness because individual agents vary in their propensity for CNS involvement and the prognosis of the neurological illness. The pathogenesis of encephalitis is heterogeneous even for a single infectious agent and may follow an acute, subacute, or chronic course. This chapter will be limited to discussing infective causes. Prion disease, metabolic or toxic encephalitides, postinfectious demyelinating disease, and encephalitis in immunodeficiency, including that caused by HIV infection, are not discussed in this chapter.
