Regional distribution of interictal 31P metabolic changes in patients with temporal lobe epilepsy

Abstract

Purpose: We compared the 31P metabolites in different brain regions of patients with temporal lobe epilepsy (TLE) with those from controls.

Methods: Ten control subjects and 11 patients with TLE were investigated with magnetic resonance imaging (MRI) and [31P]MR spectroscopic imaging (MRSI). [31P]MR spectra were selected from a variety of brain regions inside and outside the temporal lobe.

Results: There were no asymmetries of inorganic phosphate (Pi), pH, or phosphomonoesters (PME) between regions in the left and right hemispheres of controls. In patients with TLE, Pi and pH were higher and PME was lower throughout the entire ipsilateral temporal lobe as compared with the contralateral side and there were no significant asymmetries outside the temporal lobe. The degree of ipsilateral/contralateral asymmetry for all three metabolites was substantially greater for the temporal lobe than for the frontal, occipital, and parietal lobes, and these asymmetries provided additional data for seizure localization. As compared with levels in controls, Pi and pH were increased and PME were decreased on the ipsilateral side in patients with TLE. There were changes in Pi, pH, and PME on the contralateral side in persons with epilepsy as compared with controls, contrary to changes on the ipsilateral side.

Conclusions: Our findings provide some insight into the metabolic changes that occur in TLE and may prove useful adjuncts for seizure focus lateralization or localization.

FIG. 1

Example of region selection in patients with temporal lobe epilepsy. A: Saggital scout magnetic resonance imaging (MRI) scan shows the position of the 12 [³¹P]MR spectroscopy imaging ([³¹P]MRSI) slices (slice thickness 17 mm) obtained from the three-dimensional [³¹P]MRSI. Each MRSI slice corresponds to two MRI slices. B–D: Examples of selection of the occipital lobe (summed volumes), posterior hippocampus, and anterior hippocampus, respectively, using spectroscopic imaging (SID) software.

FIG. 2

Values of inorganic phosphate (Pi) (top), pH (middle), and phosphomonoesters (PME) (bottom) for ipsilateral (open circles), contralateral (solid circles), and controls (open triangles). Pi and PME are expressed as fraction of total ³¹P signal integral. AH, anterior hippocampus; H, hippocampus, PH, posterior hippocampus; LT, lateral temporal lobe; T, temporal lobe; F, frontal lobe; O, occipital lobe; P, parietal lobe. Significant differences between ipsilateral, contralateral, and control are described in the text.

FIG. 3

The individual asymmetry index ([Pi]/ [H+][PME] ipsilateral/[Pi]/[H⁺][PME] contralateral) for each region. Each number represents 1 patient with temporal lobe epilepsy (TLE). The largest asymmetry index for each patient is circled. The bars to the immediate right of the individual patient numbers indicate the 95% confidence intervals for each region calculated from the control subjects. Pi, inorganic phosphate; PME, phosphornonoesters; AH, anterior hippocampus; H, hippocampus; PH, posterior hippocampus; LT, lateral temporal from the hippocampus; T, entire temporal lobe; F, entire frontal lobe; O, entire occipital lobe; P, entire parietal lobe.