Viral Encephalitis

Japanese B encephalitis

Although Japanese B encephalitis is relatively common in Japan, Korea, India and southeast Asia, it remains an uncommon cause of viral encephalitis in Hong Kong. Japanese encephalitis virus is a flavivirus and is transmitted via mosquitos. Patients often present with a combination of headache, meningism, impaired consciousness, seizures, movement disorders, limb and bulbar muscle paralysis. MRI typically shows bilateral T2-weighted thalamic hyperintensities , which can be appreciated in the T2-weighted axial cut (Figure 1) and coronal cut of the FLAIR sequence (Figure 2) shown here. The diagnosis could be confirmed by detection of IgM antibodies in the serum and cerebrospinal fluid. The outcome is very poor with high rate of mortality.