[A case of rubella encephalitis presenting as clinically mild encephalitis/encephalopathy with a reversible splenial lesion].

A 26-year-old male was admitted because of a fever, headache and disturbance of consciousness with lymph node swelling of the neck two days after developing a rash. A neurological examination revealed restlessness with irritability in response to sensory stimuli, such as an injection. Diffusion-weighted brain magnetic resonance imaging (MRI) revealed a hyperintense ovoid lesion in the splenium of the corpus callosum, which showed a low coefficient in the ADC map: the lesion disappeared after 22 days. An enzyme immunoassay (EIA) of the serum and cerebrospinal IgM were positive for rubella virus. The patient was therefore diagnosed with rubella encephalitis. He recovered gradually and was discharged on day 19 after the onset of symptoms without any sequelae. To our knowledge, this is the first case of rubella encephalitis presenting as clinically mild encephalitis/encephalopathy with a reversible splenial lesion (MERS). Although the exact mechanism underlying the development of rubella encephalitis is not well established, this case indicated that our patient had an immune-mediated secondary encephalitis. According to the survey of the pandemic of rubella from 2012 to April 2013 in Japan, the incidence of rubella encephalitis is thought to be relatively higher than was previously noted. This emphasizes the importance of vaccination for preventing encephalitis.