Ultra-High Field Proton MR Spectroscopy in Early-Stage Amyotrophic Lateral Sclerosis

Abstract

A major hurdle in the development of effective treatments for amyotrophic lateral sclerosis (ALS) has been the lack of robust biomarkers for use as clinical trial endpoints. Neurochemical profiles obtained in vivo by high field proton magnetic resonance spectroscopy (¹H-MRS) can potentially provide biomarkers of cerebral pathology in ALS. However, previous ¹H-MRS studies in ALS have produced conflicting findings regarding alterations in the levels of neurochemical markers such as glutamate (Glu) and myo-inositol (mIns). Furthermore, very few studies have investigated the neurochemical abnormalities associated with ALS early in its course. In this study, we measured neurochemical profiles using single-voxel ¹H-MRS at 7 T (T) and glutathione (GSH) levels using edited MRS at 3 T in 19 subjects with ALS who had relatively high functional status [ALS Functional Rating Scale-Revised (ALSFRS-R) mean ± SD = 39.8 ± 5.6] and 17 healthy controls. We observed significantly lower total N-acetylaspartate over mIns (tNAA/mIns) ratio in the motor cortex and pons of subjects with ALS versus healthy controls. No group differences were detected in GSH at 3 and 7 T. In subjects with ALS, the levels of tNAA, mIns, and Glu in the motor cortex were dependent on the extent of disease represented by El Escorial diagnostic subcategories. Specifically, combined probable/definite ALS had lower tNAA than possible ALS and controls (both p = 0.03), higher mIns than controls (p < 0.01), and lower Glu than possible ALS (p < 0.01). The effect of disease stage on MRS-measured metabolite levels may account for dissimilar findings among previous ¹H-MRS studies in ALS.

Keywords: 7 T; ALS; El Escorial; ¹H magnetic resonance spectroscopy.

Fig. 1

Localized proton spectra obtained from the motor cortex (top) and pons (bottom) at 7 T using semi-LASER (TE = 26 ms, TR = 5 s, 64 averages). A 2.2 × 2.2 × 2.2 cm³ voxel (shown on T₁-weighted images) was selected in the motor cortex and angulated parallel to the slope of the dural surface in the coronal orientation. A 1.6 × 1.6 × 1.6 cm³ voxel was selected to cover nearly the entire pons region. The spectra are shown with 1-Hz exponential and 5-Hz Gaussian weighting. Left: healthy control (68 year-old female); right: subject with ALS (64 year-old female)

Fig. 2

GSH-edited spectra and GSH concentrations from the motor cortex of subjects with ALS and healthy controls using MEGA-PRESS at 3 T (TE = 68 ms, TR = 2 s, 512 averages). (a) Representative difference spectra acquired in a subject with ALS (top) and healthy control (bottom). Motor cortex voxel placement (3.5 × 2.5 × 2.3 cm³) is shown on T₁-weighted images. Spectra are shown with 1-Hz exponential line broadening and with vertical scale adjusted using NAA resonance. (b) GSH concentrations quantified using LCModel in subjects with ALS and controls; p = 0.6 from ANOVA adjusting for brain hemisphere scanned

Fig. 3

Neurochemical profiles of healthy controls and subjects with ALS obtained at 7 T (shown as mean concentration and standard deviation bars). Only neurochemicals that were quantified with mean CRLB ≤ 20% are plotted. Motor cortex: ALS (N = 19), controls (N = 17). Pons: ALS (N = 15), controls (N = 15). Asc, ascorbate; Glc+Tau, glucose+taurine; Gln, glutamine; Glu, glutamate; Glx, glutamate+glutamine; GSH, glutathione; Lac, lactate; mIns, myo-inositol; NAA, N-acetylaspartate; NAAG, N-acetylaspartylglutamate; tCho, phosphocholine+glycerophosphocholine; tCr, creatine+phosphocreatine; tNAA, N-acetylaspartate+N-acetylaspartylglutamate. *p < 0.05 from ANOVAs adjusting for brain hemisphere scanned

Fig. 4

Motor cortex NAA, mIns, and Glu levels differ between healthy controls and ALS subgroups classified by El Escorial diagnostic criteria. Controls (N = 17); ALS diagnostic subgroups: definite (N = 4), probable (N = 8), possible (N = 7). For tNAA and mIns comparisons, one-tailed Student’s t-tests were performed because the expected group differences are unidirectional. For the Glu comparison, two-tailed t-tests were performed as no such assumption was made. See Methods for details. *indicates p < 0.05