Acute and Chronic Menigiti2

Acute and Chronic Menigiti2 - pneumococcal) can cause...

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Acute and Chronic Menigitis 1. General Introduction It is helpful to distinguish meningitis from two other major categories of central nervous system (CNS) infection, namely, encephalitis and mass lesions (mainly brain abscess) because the most common causes of these syndromes are quite different. Meningitis may be caused by a variety of organisms (bacteria, viruses, fungi) whereas encephalitis is usually caused by viruses and brain abscess is usually caused by bacteria. Meningitis (inflammation of the meninges) is characterized by fever, headache, stiff neck, sometimes photophobia, and an abnormal cerebrospinal fluid (CSF) examination. Encephalitis and mass lesions usually have features of cerebral disturbance such as somnolence, seizures, and focal findings (e.g. weakness of a limb). [Some aggressive forms of meningitis (e.g. tuberculous,
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Unformatted text preview: pneumococcal) can cause vascular thromboses or even superficial cerebritis, mimicking to some extent encephalitis.] 2. Pathogenesis Infection can occur in the CNS through four routes: hematogenous spread, contiguous spread (e.g. from paranasal sinuses, middle ear), direct inoculation (after surgery or accidental trauma) and, for a few agents, by retrograde spread up nerves (HSV, rabies). Most cases of bacterial meningitis begin with infection in the nasopharynx (which may be only minimally symptomatic). The infection spreads either by the hematogenous route or directly through the pharyngeal epithelium into the CNS. Encapsulated organisms (see slide) are prime offenders because, in the absence of specific antibody, their capsules protect them against phagocytic defenses....
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