[The clinical usefulness of MRI diffusion weighted images in herpes simplex encephalitis-like cases].

We examined the serial MRI diffusion weighted images (DWIs) in two patients with acute viral encephalitis similar to herpes simplex encephalitis (HSE). Patient 1. A 27-year-old woman was admitted to the psychiatry ward for her confusional state and convulsions. Because of abnormal CSF findings she was transferred to the neurology ward, and the infusion of acyclovir was started. On disease day 5. MRI demonstrated high signal intensity in the left lateral lobe both on T2 weighted images (T2WIs) and DWIs. On day 18, MRI showed progression of the lesions, so acyclovir was changed to ara-A. On day 26, no improvement was seen clinically or radiologically. Then, combination therapy with acyclovir, ara-A and gamma-globulin was began. On day 36, she recovered completely, and abnormal intensity in MRI disappeared both on T2WIs and DWIs. Therefore, antiviral agent therapy was discontinued. Patient 2. A 31-year-old man was admitted for headache, fever and aphasia. On the next day, acyclovir was started and both DWIs and T2WIs of MRI demonstrated a high signal intensity in the left temporal lobe. Ten days later, he became perfectly well, and the increased signal intensity disappeared on DWIs, but not on T2WIs. Treatment was therefore discontinued. No relapse was in either patient. We concluded that serial MRI DWIs may be useful to determine when to discontinue the treatment in encephalitis.