Mitochondrial encephalomyopathy: elevated visual cortex lactate unresponsive to photic stimulation--a localized 1H-MRS study.

We used localized H-magnetic resonance spectroscopy (MRS) to study the metabolic changes in the visual cortex of patients with mitochondrial encephalomyopathy. Measurement of metabolite levels in the occipital visual cortex obtained in the dark with seven normal subjects and with four patients (all four of whom had Kearns-Sayre syndrome [KSS]) showed high lactate levels in the patients. Photic stimulation (PS) in four normal volunteers showed that lactate increased immediately after the start of PS and that it decreased to the baseline level with continued PS. Lactate in the resting state was higher in the KSS patients than in the controls, and, unlike the controls, the KSS patients showed no significant elevation of lactate with PS.