Japanese%20encephalitis Diagnosis

• Japanese encephalitis virus infection should be considered in a patient with evidence of a neurologic infection who has recently traveled to or resided in an endemic country in Asia or the western Pacific

Clinical and Laboratory Evaluation

Clinical Findings

• Aside from the initial signs and symptoms mentioned, classic description of Japanese encephalitis virus infection includes a Parkinsonian syndrome with masklike facies, tremor, cogwheel rigidity and choreoathetoid movements
• Seizures are usually generalized tonic-clonic that are common among children
  • Subtle focal seizures, such as twitching of an eyebrow or finger, can be important clinical findings

Diagnostic Studies

• Diagnosis of Japanese encephalitis virus infection is confirmed by detection of Japanese encephalitis virus-specific immunoglobulin M (IgM) antibodies in cerebrospinal fluid (CSF) or serum by enzyme-linked immunoabsorbent assay (ELISA)
  • Presence of Japanese encephalitis virus IgM in CSF confirms infection of the central nervous system and can help distinguish clinical disease attributed to Japanese encephalitis virus from previous vaccination
  • While presence of Japanese encephalitis virus IgM in serum indicates recent Japanese encephalitis virus vaccination or asymptomatic infection
• Japanese encephalitis virus-specific IgM antibodies are usually detectable 3-8 days after onset of illness and persists for 30-90 days, but longer persistence has been documented
  • Japanese encephalitis virus-specific IgM antibodies can be measured in the CSF of most patients by 5-8 days after onset of symptoms and in serum by ≥9 days after onset
• To measure virus-specific neutralizing antibodies, plaque reduction neutralization tests (PRNT) can be performed
• Vaccination history, date of onset of symptoms and information regarding other arboviruses known to circulate in the geographic area that might cross-react in serologic assays should be considered when interpreting results

Laboratory Findings

• May include moderate leukocytosis, mild anemia and hyponatremia due to inappropriate antidiuretic hormone secretion
• Thrombocytopenia and elevated hepatic enzymes have been noted
• CSF opening pressure is elevated and has mild to moderate pleocytosis with lymphatic predominance, slightly elevated protein and normal ratio of CSF to plasma glucose

Imaging Studies

• Magnetic resonace imaging of the brain most commonly shows thalamic lesions
  • Not a very sensitive marker for Japanese encephalitis virus but these can be highly specific for Japanese encephalitis virus in the appropriate clinical context
• EEG abnormalities may include theta and delta coma, burst suppression, epileptiform activity and occasionally alpha coma

• Other viral encephalitides, other CNS infections, para- or postinfectious causes, and noninfectious diseases
• Domestic arboviral infections (eg La Crosse, St Louis encephalitis, Eastern equine encephalitis, Powassan viruses)