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Encephalitis is an inflammation of the brain that can occur with or without associated meningeal irritation; the
former is termed meningoencephalitis, but the terms will be used interchangeably in this section. The clinical
manifestations can overlap with those of meningitis. The etiologies most commonly associated with encephalitis
are listed in
e-Table 94.2 ; however, an etiology is found in only a small fraction of children and adults with
encephalitis. In circumstances where etiologies are found, almost 70% are viral (most commonly enterovirus,
followed by HSV and Epstein–Barr virus [EBV]) and approximately 20% are bacterial. In the last two decades, it
has been recognized that several arboviruses endemic in the United States can cause encephalitis. These viruses,
which include West Nile, St. Louis, La Crosse, and the equine encephalitides, are termed arbo viruses because they
are ar thropod-bo rne viruses, not because they share phylogenetic characteristics. The clinical manifestations
include altered consciousness or behavioral changes, seizures, hemiparesis, or ataxia, often with nausea and
vomiting. Fever is not uniformly present. Postinfectious cases can have associated demyelination in the absence of
acute signs of infection; most cases of brainstem encephalitis are postinfectious. The differential diagnosis of
encephalitis includes ingestion, metabolic disorders, structural lesions (masses, bleeds, emboli), acute
demyelinating encephalomyelitis (ADEM), and autoimmune encephalitis (NMDAR). One diagnostic approach to
the child with suspected encephalitis is listed in Table 94.10 , realizing that repeated history taking may be
necessary to elucidate all exposures a child may have had. Children with encephalitis should be started on
acyclovir (20 mg/kg every 8 hours) pending HSV PCR, as this is one of the few treatable causes of encephalitis. If
a CSF pleocytosis exists, empiric initiation of parenteral antibiotics (e.g., vancomycin [15 mg/kg every 6 hours]
and cefotaxime [75 mg/kg every 6 hours; maximum: 2 g/dose]) is reasonable pending bacterial culture results.
Consideration should be given to admission of these patients to intensive care unit settings for closer monitoring
given concerns for changes in the ability to protect the airway, increased intracranial pressure, or electrolyte
imbalances. Standard precautions are recommended for most forms of encephalitis.