[A case of herpes simplex encephalitis with cerebral white matter lesion after acyclovir administration].

Herpes simplex virus (HSV) is regarded as an agent that selectively affects temporal and frontal lobes with necrosis and hemorrhage, and no case of herpes simplex encephalitis (HSE) with white matter lesion in a diffuse fashion has previously been reported. A 2-year-old boy developed high fever, right hemi-convulsions and lethargy. Computed tomography (CT) showed wedge-shaped areas of high density in the left frontal region, whereas, cerebral angiography disclosed no vascular abnormality. T1-weighted magnetic resonance imaging (MRI) demonstrated cortical changes which were similar to those illustrated by CT. However, T2-weighted images depicted further spread high intensities of the lesion. The patient's symptoms spontaneously disappeared before an antiviral drug, acyclovir, was administered. After the significant increase of HSV antibody titers in serum and cerebro-spinal fluid (CSF) established a definite diagnosis, acyclovir was intravenously given at a daily dosage of 30 mg/kg for a period of 6 days in order to prevent the recurrence of HSE. Two months later, T2-weighted MRI visualized a diffuse lesion of increased signal intensities involving the white matter of both hemispheres, while both CSF protein and myelin basic protein were significantly elevated. Despite of these changes of the white matter, our patient developed a few symptoms such as mild speech disturbance, slight weakness of the right upper limb and sialorrhea. Although the mechanism of these changes in the white matter remains obscure, it is postulated that a direct invasion of HSV to the white matter, an immunological disorder following HSV infection and a side effect of acyclovir could have triggered a reversible process of demyelination of the cerebral white matter.