[A case of Japanese encephalitis presenting with unilateral lesions in diffusion-weighted MRI].

We report the findings of diffusion-weighted MRI (DWI) taken serially in a patient with Japanese encephalitis (JE). The patient was a 43-year-old woman presenting with headache, high fever and consciousness disturbance. The diagnosis of JE was made based on more than fourfold elevation of serum complement fixation antibody titer for JE virus in the convalescent phase of illness. The DWI on the second day of illness (Day-2) disclosed high-signal intensity lesions in the left thalamus, substantia nigra and frontal lobe cortex. The signal intensity of these lesions on the DWI increased on Day-3 but gradually decreased thereafter and normalized on Day-28. The improvement of the DWI findings was paralleled with that of the consciousness level and the cell number and neuron specific enolase concentration in the CSF, suggesting that DWI is useful for evaluation of the disease activity in JE. The lesions in the brain suffering from Japanese encephalitis are usually bilateral and diffuse. To our knowledge, this is the first report of JE presenting with unilateral lesions on MRI, of which phathomechanism remains to be elucidated.