California Encephalitis Workup
- Author: Wayne E Anderson, DO; Chief Editor: Burke A Cunha, MD more...
Approach Considerations
According to the Centers for Disease Control and Prevention (CDC) guidelines for the diagnosis of arboviral encephalitis, febrile illness or mild aseptic meningitis or encephalitis (with onset during a period when the transmission of the virus is likely) occurs with one of the following:
- A 4-fold increase in the antivirus antibody titer between the acute and the convalescent periods
- Virus isolation from tissue, blood, or cerebrospinal fluid (CSF); note that La Crosse virus has not been isolated from CSF
- Specific immunoglobulin M (IgM) antibodies to the virus detected using enzyme-linked immunosorbent assay (ELISA) technique during the acute illness
Antibody studies
Significant antibody titers include levels of more than 320 by hemagglutination inhibition, more than 128 by complement fixation, more than 256 by immunofluorescence, or more than 160 by plaque reduction neutralization test.
CSF examination
CSF examination reveals the following:
- Normal to mildly elevated pressure level
- Normal glucose level and normal to mildly elevated protein level
- Initially, a polymorphonuclear leukocytic pleocytosis followed by lymphocytic or monocytic leukocytosis is present.
Complete blood count
The complete blood count (CBC) is usually within the reference range or might show mild leukocytosis. Chemistries are usually within the reference range.
Polymerase chain reaction
Use of the polymerase chain reaction for the diagnosis of La Crosse encephalitis is still in the research stage.
Electroencephalography
De los Reyes and colleagues found that children with La Crosse encephalitis who have PLEDS on electroencephalograms have a higher rate of complications.[4]
CT Scanning and MRI
Neuroimaging using conventional computed tomography (CT) scanning and magnetic resonance imaging (MRI) is not helpful in establishing the diagnosis of California encephalitis. In very severe cases, CT scanning might show nonspecific enhancement. (See the image below.)
Left image of a CT scan of an 8-year-old boy with severe La Crosse encephalitis complicated by uncal herniation (obtained on the second hospital day) reveals brain edema with associated obliteration of perimesencephalic cisterns (arrows). On the right, a T2-weighted magnetic resonance image obtained from a 7-year-old boy with severe La Crosse encephalitis shows focal areas of increased signal intensity in the right temporoparietal and left frontotemporal regions (arrows). Histologic Findings
On pathologic examination, as with all viral encephalitides, there is a widespread degeneration of single nerve cells, with neuronophagia and scattered foci of inflammatory necrosis involving the gray and white matter. The brain stem is relatively spared. Perivascular cuffing with lymphocytes and plasma cells occurs, as well as patchy infiltration of the meninges. (See the image below.)
Brain biopsy specimen from a 7-year-old boy with severe La Crosse encephalitis (hematoxylin and eosin stain, 200X). Perivascular infiltration with mononuclear cells is present on light microscopy. This biopsy material tested positively for La Crosse virus antigen on direct immunofluorescence assay. Halperin JJ, ed. Encephalitis: Diagnosis and Treatment. New York, NY: Informa Healthcare; 2008.
Sokol DK, Kleiman MB, Garg BP. LaCrosse viral encephalitis mimics herpes simplex viral encephalitis. Pediatr Neurol. Nov 2001;25(5):413-5. [Medline].
Wurtz R, Paleologos N. La Crosse encephalitis presenting like herpes simplex encephalitis in an immunocompromised adult. Clin Infect Dis. Oct 2000;31(4):1113-4. [Medline].
de los Reyes EC, McJunkin JE, Glauser TA, Tomsho M, O'Neal J. Periodic lateralized epileptiform discharges in La Crosse encephalitis, a worrisome subgroup: clinical presentation, electroencephalogram (EEG) patterns, and long-term neurologic outcome. J Child Neurol. Feb 2008;23(2):167-72. [Medline].
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