MR findings in Murray Valley encephalitis

Summary: Murray Valley encephalitis (MVE) is caused by a flavivirus related to West Nile and St. Louis encephalitis viruses. We report a case of MVE resulting in quadriplegia and respiratory failure. MR imaging demonstrated thalamic hyperintensity on T2-weighted images, with similar involvement of the red nucleus, substantia nigra, and cervical cord. These findings preceded serologic diagnosis and are similar to those of Japanese encephalitis. In the appropriate setting, thalamic T2 hyperintensity is suggestive of flavivirus infection.

Murray Valley encephalitis (MVE) is caused by infection with a flavivirus belonging to the Japanese encephalitis (JE) antigenic complex, which also includes St. Louis encephalitis (StLE) and West Nile (WN) virus. The natural transmission cycle of the JE group involves infection of a mosquito vector alternating with viral amplification in a variety of vertebrate hosts. Human disease is incidental to this cycle. They are neurotropic viruses, which are becoming increasingly important globally as their geographic ranges steadily increase. WN virus, for example, has recently caused a major epidemic of flaccid paralysis in New York (1), and cases of JE have now been reported in northeastern Australia, where the virus may have become established in the wild pig population (2). The radiologic features of JE (3) and StLE (4) have been reported recently. Herein we describe the MR findings in a case of severe MVE. To our knowledge, these findings have not been described previously and correlate well with both the known clinical features of the disease and with the neurotropism of other members of the JE group.