Diffusion Tensor MRI and MR Spectroscopy in long lasting upper motor neuron involvement in Amyotrophic Lateral Sclerosis

Abstract

Upper motor neuron (UMN) dysfunction in Amyotrophic Lateral Sclerosis (ALS) is not easy to identify clinically: Diffusion Tensor Imaging (DTI) and single-voxel Magnetic Resonance Spectroscopy (H-MRS) can identify markers of UMN involvement. The aim of this study was to correlate brain DTI and MRS data with clinical parameters in ALS patients (PALS).We studied 32 PALS using Magnetic Resonance Imaging. The subjects were subdivided into definite/probable (D/P) and possible/suspected (P/S). DTI indices included Fractional Anisotropy (FA) and averaged Apparent Diffusion Coefficient (avADC). Anatomical areas were sampled by positioning regions of interest along cortico-spinal tracts, from the precentral cortex to the bulb. H-MRS voxels were localized bilaterally in precentral regions.D/P-PALS showed significantly lower FA values than healthy controls in almost all regions, whereas P/S-PALS FA values were significantly lower only in the left precentral gray matter (GM), right precentral white matter (WM), cerebral peduncles (CP), left hemipons, and left bulbar pyramid (BP).Significantly higher avADC values were observed in the D/P-PALS right precentral GM, precentral WM, right semioval center-posterior limb of the internal capsule (SC-PLIC), and left CP; and in the precentral WM, right SC-PLIC, left CP, and right hemipons of P/S-PALS.With increasing disability, only D/P-PALS showed significantly reduced FA values in the left precentral WM and hemipons, and increased avADC values in the precentral WM.Significantly lower N-acetylaspartate (NAA)/creatine-phosphocreatine complex (Cr) and higher choline (Cho)/Cr and myoinositol (mI)/Cr ratios were found in D/P-PALS, while only higher Cho/Cr and mI/Cr ratios were found in P/S-PALS.Our data highlight the usefulness of DTI and H-MRS in assessing UMN involvement. Given FA sensitivity and specificity, despite the small number of PALS, our findings support its use as a diagnostic marker in D/P-PALS.