Pediatric emergency medicine trisk 2635 2635
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encephalitis. West Nile virus is another agent in this family that first appeared in
the United States in 1999. Since then, it appears to have become endemic in large
parts of North America, although clinically overt infections in children are
uncommon.
Infection with rabies virus, although rare in the United States, is an important
cause of encephalitis worldwide. Nonviral pathogens, including Mycoplasma
pneumoniae, Lyme disease, and rickettsiae, may also cause encephalitis.
Viral encephalitis usually follows a viremia, although direct spread can occur
less commonly via peripheral nerves or the nasal mucosa. Viral replication in
neural cells interferes with cellular function and may lead to cell death. The
extent of neuronal dysfunction depends on the pathogen and host factors,
especially immunocompetence. The clinical picture of viral encephalitis ranges
from a mild febrile illness associated with headache and minimal changes in
mentation to a severe, fulminant presentation with coma, seizures, and death. The
onset may be abrupt or insidious. Typical features consist of fever, headache,
vomiting, and signs of meningeal irritation. Altered consciousness, ataxia, and
seizures are also seen (see Chapters 15 Acute Ataxia and 17 Coma ). Focal
neurologic deficits may occur in certain types of encephalitis, particularly HSV.
Flaccid paralysis may be seen in cases of encephalomyelitis, and rarely,
respiratory or autonomic dysfunction results from brainstem involvement. Rash
or mucous membrane lesions are often seen with the exanthematous viruses such
as measles and varicella; however, cutaneous findings are uncommon with HSV
encephalitis.
The diagnostic evaluation of viral encephalitis should be tailored based on
clinical and epidemiologic clues and requires a thorough clinical history.
Determining if a patient is immunocompromised, if they have had a recent illness,
as well as assessing their travel history and immunization status can help
determine a likely etiology. Unless contraindicated, CSF collection for virus
isolation is recommended in all patients with suspected encephalitis. Additionally,
HSV PCR should be performed on all CSF samples as early identification and
treatment may decrease morbidity and mortality. Newer PCR-based detection
panels can test for multiple viral and bacterial pathogens. Viral isolation from
other body sites, including the nasopharynx, skin lesions, urine, and feces, should
be completed as clinically indicated. Neuroimaging is recommended in the
evaluation of encephalitis in order to exclude noninfectious alternative diagnoses,
and MRI with diffusion-weighted imaging is the study of choice. Additionally,
certain encephalitides have characteristic patterns on MRI that may offer a
diagnostic clue. Similarly, electroencephalography (EEG) is recommended as it is
