Encephalitis is the second most common type of infection of the central nervous system and continues to be an important cause of mortality and morbidity.
In a patient who is suspected of having encephalitis, one must distinguish between encephalitis and encephalopathy and between infectious encephalitis and acute disseminated encephalomyelitis. Once infectious encephalitis has been diagnosed, one should determine whether the patient has herpes simplex encephalitis, because treatment with antiviral drugs such as acyclovir greatly improve outcome. Most cases of infectious encephalitis are due to viruses, but bacteria, fungi, and parasites also can be the cause, especially in immunosuppressed individuals. The rapid determination of the cause of infectious encephalitis remains difficult, but newer assays to detect IgM antibody to the infectious agent in CSF or serum and polymerase chain reaction assays for nucleic acid fragments of the infectious agent in CSF are enabling faster and more accurate diagnoses. Antimicrobial drugs now are available for many of the infectious agents and some DNA viruses, but excellent treatment of the patient's symptoms remains very important.
This review provides an approach to diagnosing possible encephalitis through asking and answering several key questions. Recent advances in methods of determining the cause of the encephalitis and better antimicrobial drugs improve the likelihood of successful treatment.
(THE NEUROLOGIST 6:145-159, 2000)