[Proton MR spectroscopy findings in herpes simplex encephalitis].

Localized proton magnetic resonance spectroscopy (1H-MRS) was conducted in two patients with herpes simplex virus type I encephalitis (HSE). MR spectra of bilateral temporal lobes were acquired by the single voxel method using 1.5T unit. Peaks indicating N-acetyl aspartate (NAA), choline (Cho) and creatine including phosphocreatine (Cr) were identified and ratios of NAA/Cr and Cho/Cr were calculated. These ratios were compared with those of the contralateral side showing normal MRI findings and also with the control spectra obtained from normal volunteers. Three abnormal findings were observed in the spectra of the patients suffering from HSE; 1. significant reduction of the NAA/Cr ratio at the involved temporal lobe, 2. mild reduction of the NAA/Cr ratio at the normal temporal lobe, and 3. elevation of the Cho/Cr ratio at the bilateral lobes, but more significant on the involved sides. These results indicated that neural loss and gliosis occurred in the contralateral area with normal MR images as well as the involved hemisphere. We concluded that 1H-MRS is able to show the specific histological findings of herpes simplex encephalitis. This is the first report assessing 1H-MRS for patients with HSE in Japan.