[Japanese encephalitis presenting with left hemiplegia and thalamic neglect--a case report].

This report concerns a 51-year-old right-handed man with Japanese encephalitis, showing left hemiplegia and left hemispatial neglect. On admission, he had a slight fever, mild consciousness disturbance, left hemiplegia, and left hemispatial neglect but no neck stiffness, headache nor nausea. He was treated on the basis of cerebral infarction, but his fever and consciousness disturbance worsened. We found pleocytosis (145/mm3) in the cerebrospinal fluid (CSF) and right thalamic edema on a brain CT scan obtained 4 days later. He was finally diagnosed as having Japanese encephalitis on the basis of an increase in anti-viral antibodies observed in paired CSF and serum samples. In the exacerbation phase, 123I-IMP single photon emission CT (SPECT) demonstrated a marked decrease in cerebral perfusion in the right hemisphere, while a brain MRI revealed irregular lesions localized the right thalamus (mainly posterior and medial parts), showing low intensity on T1-weighted and high intensity on T2-weighted images. In the recovery phase, asymmetrical perfusion was no longer observed on SPECT and the symptoms including the left hemispatial neglect had improved. These findings suggest that the left hemispatial neglect in this patient might been caused by the right thalamic lesion resulting in damage to the activating system of the right hemisphere. This case thus shows that acute onset of hemispatial neglect could be caused by cerebral encephalitis.