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Chapter 2 : Diagnostic Evaluation
The diagnosis of encephalitis is suggested when brain dysfunction is accompanied by evidence of central nervous system (CNS) inflammation. In the elderly, infection of other organ systems such as the lungs or gastrointestinal tract may be followed by fluid and electrolyte imbalance, reduced oxygenation of the blood, and impaired caloric intake. Definition of the specific etiology of a case of encephalitis is important for several reasons. First, by identifying the etiologic agent or mechanism, the patient is spared with therapies and diagnostic maneuvers directed at other potential etiologies. Second, the clinician is able to be more specific in the projection of the possible course and outcome of the illness. Third, the information is of public health importance. The examination and laboratory evaluation of a case of encephalitis is an exercise in both clinical neurology and diagnostic virology. The neurological history, examination, and diagnostic studies can determine the anatomic location of dysfunction in the nervous system, distinguish encephalitis from other categories of disease, and sometimes suggest the specific viral etiology. Virologically oriented studies must proceed in stride with the clinical neurological studies. The need for rapid viral diagnosis is propelled by the increasing number of specific antivirals available for treatment. Dramatic advances in the diagnosis and treatment of acute viral diseases have revolutionized patient care.