Fiber‐specific white matter analysis reflects upper motor neuron impairment in amyotrophic lateral sclerosis

• Published in: European journal of neurology Vol. 29; no. 2; pp. 432 - 440
• Main Authors: Ogura, Aya, Kawabata, Kazuya, Watanabe, Hirohisa, Choy, Shao Wei, Bagarinao, Epifanio, Kato, Toshiyasu, Imai, Kazunori, Masuda, Michihito, Ohdake, Reiko, Hara, Kazuhiro, Nakamura, Ryoichi, Atsuta, Naoki, Nakamura, Tomohiko, Katsuno, Masahisa, Sobue, Gen
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.02.2022
• Subjects: Amyotrophic lateral sclerosis; Brain; Corpus callosum; corticospinal tract; diffusion‐weighted imaging; Error correction; fixel‐based analysis; Morphometry; Neuroimaging; Patients; Pyramidal tracts; Reduction; Substantia alba; upper motor neuron signs; fixel-based analysis; upper motor neuron signs; diffusion-weighted imaging; amyotrophic lateral sclerosis; corticospinal tract
• ISSN: 1351-5101; 1468-1331
• DOI: 10.1111/ene.15136

Background and purpose To clarify the relationship between fiber‐specific white matter changes in amyotrophic lateral sclerosis (ALS) and clinical signs of upper motor neuron (UMN) involvement, we performed a fixel‐based analysis (FBA), a novel framework for diffusion‐weighted imaging analysis. Methods We enrolled 96 participants, including 48 nonfamilial ALS patients and 48 age‐ and sex‐matched healthy controls (HCs), in this study and conducted whole‐brain FBA and voxel‐based morphometry analysis. We compared the fiber density (FD), fiber morphology (fiber cross‐section [FC]), and a combined index of FD and FC (FDC) between the ALS and HC groups. We performed a tract‐of‐interest analysis to extract FD values across the significant regions in the whole‐brain analysis. Then, we evaluated the associations between FD values and clinical variables. Results The bilateral corticospinal tracts (CSTs) and the corpus callosum (CC) showed reduced FD and FDC in ALS patients compared with HCs (p < 0.05, familywise error‐corrected), and the comparison of FCs revealed no region that was significantly different from another. Voxel‐based morphometry showed cortical volume reduction in the regions, including the primary motor area. Clinical scores showed correlations with FD values in the CSTs (UMN score: rho = −0.530, p < 0.001; central motor conduction time [CMCT] in the upper limb: rho = −0.474, p = 0.008; disease duration: rho = −0.383, p = 0.007; ALS Functional Rating Scale‐Revised: rho = 0.340, p = 0.018). In addition, patients whose CMCT was not calculated due to unevoked waves also showed FD reduction in the CSTs. Conclusions Our findings suggest that FD values in the CST estimated via FBA can be potentially used in evaluating UMN impairments. Fixel‐based analysis revealed reduced fiber density (FD) in the corticospinal tracts (CSTs) in amyotrophic lateral sclerosis patients. The FD reduction in the CSTs and upper motor neuron (UMN) impairments were correlated. We report that FD values in the CST estimated via FBA can be potentially used in evaluating UMN impairments.