Infections of the nervous system

The chapter begins with a discussion of common major clinical features and mechanisms of damage produced by infections of the central nervous system (CNS). Viruses, bacteria, fungi, and parasites cause CNS infections. Most organisms reach the central nervous system via the blood stream after entering the body via the gastrointestinal tract, respiratory tract, or following skin inoculation (animal or insect bites). The CNS evolved differently from other systemic organs and did not develop a sensitive immune surveillance system. Instead, a blood–brain barrier evolved to prevent infectious organisms from entering the CNS. Unfortunately, if an infectious organism successfully enters the CNS, there are limited defenses to fight the infection. The signs and symptoms of a CNS infection depend on the site of the infection and not the infectious organism. Major sites of infections are diffusely in the meninges (meningitis), diffusely in the brain (encephalitis), and focally in the brain (abscess). The organism determines the time course and severity of the infection. This chapter then discusses major types of central and peripheral nervous system infections: bacterial and viral meningitis, brain abscess, encephalitis, prion Creutzfeldt–Jakob disease, herpes zoster or shingles, and paraneoplastic limbic encephalitis that mimics encephalitis. Attention is paid to their pathophysiology, major clinical features, major laboratory findings, and principles of management and prognosis.