[Serial MRI, SPECT and 1H-MRS findings in a case of herpes simplex encephalitis]

We report herein a case of herpes simplex encephalitis (HSE) in which magnetic resonance imaging (MRI), single photon emission computed tomography (SPECT) and proton magnetic resonance spectroscopy (1H-MRS) were performed sequentially. Both MRI and SPECT demonstrated a lesion on the left temporal lobe in its early stage. However, SPECT seemed more sensitive because it could detect subtle alterations of the blood flow. Hyperperfusion identified by SPECT had returned to normal levels while the abnormal MRI findings still remained. This may indicate that normalization of the blood perfusion precedes the tissue recovery. Contrast enhancement using Gd-DTPA was observed along the surface of the cerebral cortex on MRI, but that involved only part of the hyperperfusion areas depicted with SPECT. In the affected left temporal lobe, 1H-MRS exhibited reduction of N-acetyl-asparate (NAA), and an elevated lactate level. The former represented the neuronal loss, and the latter indicated impairment of oxidative metabolism. Furthermore, alterations of NAA/creatine (Cr) and choline (Cho)/Cr ratios were also observed in the seemingly normal right temporal lobe. Those ratios returned to nearly normal levels in accordance with the patient's clinical recovery. Subsequently, our results indicate that 1H-MRS might be a very useful tool in qualifying the tissue damage and possibly estimating the prognosis.